Star Formation in Bok Globules and Small Clouds

Home , Bok globule, Reflection nebula, Sagitta

Handbook of Star Forming Regions Vol. II Astronomical Society of the Paciﬁc, c 2008 Bo Reipurth, ed.

Bo Reipurth Institute for Astronomy, University of Hawaii 640 N. Aohoku Place, Hilo, HI 96720, USA

Abstract. While most star formation occurs in giant molecular clouds, numerous small clouds and Bok globules are known to each harbor one or a few young stars. Studies of such isolated newborn stars offer insights into the star formation process unencumbered by the confusion that often complicates studies of richer star forming regions. In this chapter, a dozen Bok globules and small clouds have been selected for discussion as examples of small scale star formation. Particularly interesting or well studied cases include BHR 71, CG 12, B62, B93, L723, and B335.

1. Introduction

Many Bok globules are known across the sky, and small clouds and cloud fragments are found even more commonly. Despite their numbers, these small objects are not an important contributor to the production of low-mass stars in our Galaxy, accounting for at most a few percent (Reipurth 1983). The importance of these regions lies mostly in their simplicity, which allows us to study the formation of one or a few stars without the confusion that often complicates observations of richer regions of star formation. Bok globules are now widely regarded as remnant cloud cores that have been ex- posed due to the presence of nearby OB stars (Reipurth 1983). The specific processes involved has been under some debate among theoreticians (e.g., Sandford, Whitaker, & Klein 1984, Bertoldi 1989, Lefloch & Lazareff 1994, Kessel-Deynet & Burkert 2003, Miao et al. 2006). While observational evidence for star formation in Bok globules was late in coming (e.g., Bok 1978, Reipurth 1983, Yun & Clemens 1990), numerous cases of star formation in globules are now known. Many surveys have been made of globules at various wavelengths, including Clemens & Barvainis (1988), Yun & Clemens (1992), Bourke, Hyland, & Robinson (1995), Bourke et al. (1995), Wang et al. (1995), Launhardt & Henning (1997), Henning & Launhardt (1998), Launhardt et al. (1998), Huard, Sandell, & Weintraub (1999), Moreira et al. (1999), Ogura, Sugitani, & Pickles (2002), and Kandori et al. (2005). The distinction between a Bok globule and a small cloud is diffuse, as are the terms themselves. The term globule originated in the papers by Bok & Reilly (1947) and Bok (1948), who already then noted that “It is not a simple matter to draw the line between true globules and minor condensations in dark lanes or in regions of variable obscuration.” Bok & Reilly distinguished between small globules, which are seen in contrast against bright HII regions, and large globules; it is these latter that are now known as Bok globules. On empirical grounds, Bok considered these objects to be “compact mostly near-circular dark nebulae” with diameters typically between 3 and 20 arcmin, corresponding to radii likely in the range 0.15 to 0.8 pc (Bok 1977). A number of very interesting star forming clouds exist which are sometimes not much 1 2 larger than Bok globules, and for lack of a better term they are here denoted as “small clouds”. Some clouds, like L810, which have the shape and angular diameter to fall in the category of Bok globules turn out to have such large distances that they do not qualify as bona fide Bok globules, and they too are considered small clouds. Many cases of star formation in globules and small clouds are presented through- out this Handbook, for example cometary globules in the Gum Nebula are discussed in the chapter on Puppis-Vela, B68 and FeSt 1-457 are presented in the chapter by Alves et al., the globules B362 and L1014 are discussed in the chapter on Cygnus, and numerous small clouds are reviewed in the chapter on Cepheus. So many cases are known across the sky that it would be impossible to discuss all here. The following is therefore a very limited selection rather than an attempt to do a more comprehensive presenta- tion (see Table 1). Inevitably the discussion focuses on globules or small clouds that have caught the interest of the author, but hopefully the selection is representative of the many known cases of star formation in globules and small clouds. The sections are ordered after right ascension.

Table 1. Bok Globules and Small Clouds discussed in this Chapter

Object α2000 δ2000 l b Other ID’s L1438 04:56.9 +51:31 156.2 +5.3 L1439 05:00.1 +52:05 156.1 +6.0 CB26 CB54 07:04.4 –16:23 229.0 –04.6 BHR71 12:01.7 –65:09 297.7 –2.7 Sa136,TGU1840 CG12 13:57.6 –39:59 316.5 +21.1 BHR92,TGU1970,MBM112 L43 16:34.5 –15:47 1.4 +21.0 TGU23 B62 17:15.9 –20:56 3.1 +10.0 L100 B92 18:15.5 –18:11 12.7 –0.6 L323,CB125,TGU135 B93 18:16.9 –18:04 13.0 –0.8 L327,CB131 L483 18:17.5 –04:40 24.9 +5.4 TGU259/P1 L723 19:17.9 +19:12 53.0 +3.0 B335 19:36.9 +07:34 44.9 –6.5 L663,CB199 L810 19:45.4 +27:51 63.6 +1.7 CB205

2. Individual Bok Globules and Small Clouds

2.1. V347 Aur in L1438 L1438 is the central core in a low-extinction cloud complex encompassing many small cores, including L1429, L1430, L1431, L1432, L1433, L1435, L1436, L1437, L1438, and L1439 (CB26) in the catalog of Lynds (1962). The cloud complex is known as TGU 1046 in the cloud atlas of Dobashi et al. (2005), where L1438 is listed as the core TGU 1046 P1. The region is located at the intersection between Auriga, Perseus, and Camelopardalis, see Figure 1 in the chapter by Straizys & Laugalys in Volume I of this Handbook. L1438 harbors the variable star V347 Aur = HBC 428 = IRAS 04530+5126 ◦ ◦ (α2000 4:56:57.0, δ2000 +51:30:51; l = 156.2 , b = 5.3 ), ﬁrst recognized as variable by Morgenroth (1939). A more detailed photographic study of the light variations was made by Wenzel (1978), who found that V347 Aur had four maxima that were consistent with a period of about a year. V347 Aur is surrounded by a small reﬂection nebula 3

Figure 1. V347 Aur in its small globule L1438. From the Digitized Sky Survey. known as GM 1-3 (Gyulbudaghian & Magakian 1977), PP 24 (Parsamian & Petrosian 1979), or RNO 33 (Cohen 1980), see Figure 1. A low-dispersion spectrum was taken by Cohen, who noted a rich emission line spectrum superposed on a late-type spectrum. Herbig (priv. comm.) has obtained several high-resolution spectra of V347 Aur, which show very signiﬁcant spectral variability. Magakian et al. (2008) has discovered a Herbig-Haro object, HH 715, near V347 Aur. The distance to L1438 is unknown, but its proximity to another globule, L1439 (see next section), might suggest that it is at about the same distance, ∼140 pc.

2.2. L1439 About half a degree from L1438 is another small globule, L1439, also known as CB 26 (Clemens & Barvainis 1988). As can be seen in Figure 2, the globule is about 5 ar- cminutes across, and has a faint luminous rim and tail that is facing towards the WSW. Launhardt & Henning (1997) suggested a distance of 300 pc, but based on kinematic arguments Launhardt & Sargent (2001) proposed that L1439 is part of the Taurus-Auriga complex at a distance of about 140 pc. The IRAS 04559+5200 source is located towards L1439. Stecklum et al. (2004) have obtained near-infrared images of the globule, and find a bipolar reflection nebula, bisected by a high extinction lane, suggesting the presence of an edge-on circumstellar disk. Using near-infrared imaging polarimetry, Stecklum et al. (2004) find that the illuminator is located towards the center of the extinction lane. About 6 arcmin to the 4

Figure 2. The globule L1439 = CB 26 as seen on the red Digitized Sky Survey. The ﬁeld is 15′ × 15′, and north is up and east is left.

Figure 3. The globule CB 54 as seen on the red Digitized Sky Survey. The ﬁeld is 15′ × 15′, and north is up and east is left. 5

NNW of the embedded source and along an axis perpendicular to the extinction lane, Stecklum et al. (2004) noted a Herbig-Haro object, HH 494. Henning et al. (2001) used SCUBA to detect a 850 µm source towards the IRAS source. More detailed observations were done by Launhardt & Sargent (2001) with the Owens Valley Radio Observatory millimeter-wave array in the continuum at 1.3 and 2.7 mm, revealing an extended structure about 400 AU wide that precisely coincides with the extinction lane seen in the near-infrared. Additional 13CO (1-0) data display a Keplerian rotation pat- tern about an axis perpendicular to the disk. The central illuminating source has a total luminosity of only ∼0.5 L⊙ and an energy distribution consistent with a Class I source (Stecklum et al. 2004).

2.3. CB 54 CB 54 is a small globule from the catalog of Clemens & Barvainis (1988) and located a little below the Galactic plane in Canis Major. It is associated with a bright rim (see Figure 3) and is listed as LBN 1042 in the catalog of bright nebulae by Lynds (1965). Launhardt & Henning (1997) adopted a distance of 1.5 kpc, but Henning et al. (2001) recognized the probable association of CB 54 with the molecular complex containing the nebula BBW 4, for which Brand & Blitz (1993) suggest a kinematic distance of 1.1 kpc.

Figure 4. The core of the CB 54 globule as seen in the K-band with 2MASS with known objects identiﬁed. The cross marks the position of IRAS 07020–1618, and the large dotted circle shows the 850 µm source. The dashed box outlines the area imaged in the mid-infrared, and white circles with plusses indicate the mid- infrared sources detected. The open square marks the VLA centimeter radio continuum source, and the open diamond is an 8 µm MSX source. From Ciardi & G´omez Mart´ın 2007). 6

The globule is associated with the embedded object IRAS 07020–1618, a Class I source that drives a bipolar molecular outflow with well separated lobes oriented NNE to SSW (Yun & Clemens 1994). Wang et al. (1995) obtained a map of CB 54 in 18 the C O (2-1) line and found a dense 100 M⊙ core centered on the IRAS source. Analysis of the line profiles suggest moderate evidence for infall motion in the core. In a follow-up study, Zhou et al. (1996) used the BIMA interferometer to do aperture synthesis observations of CB 54 in the 13CO (1-0) and C18O (1-0) lines, but the collapse signatures were not found, probably because of confusion with the outflow wings. Yun (1996) obtained near-infrared images of CB 54, and studied two sources separated by about 10′′ and labeled YCI and YCII, the latter is associated with a red reflection nebula. Additional nebulosity, known as YCI-SW, is located at the center of the IRAS uncertainty ellipse. An 850 µm map of the globule by Henning et al. (2001) reveal a cool source coincident with the IRAS source, and this is also the location of a water maser detected by Gómez et al. (2006) and studied in more detail by de Gregorio- Monsalvo et al. (2006). A thermal centimeter radio continuum source has been found in CB 54 five arcseconds southeast of YCI with the VLA (Yun et al. 1996, Moreira et al. 1997). In a detailed mid-infrared study of CB 54, Ciardi & Gómez Mart´ın (2007) have found a small cluster of mid-infrared sources that are spatially coincident with the dense core and submillimeter source found towards the IRAS 07020–1618 source and the YCI-SW nebula (see Figure 4). They additionally note that YCII is likely a Class I source, whereas the nondetection of YCI at mid-infrared wavelengths suggests it is in a more evolved stage or a background object. Altogether, the currently available data indicate that CB 54 harbors a small cluster of young stars in early evolutionary stages.

2.4. BHR 71 In a survey for southern dark clouds, Sandqvist (1977) cataloged a small cloud, Sa 136, in the southern constellation of Musca just south-west of the Coalsack (it is seen in Figure 1 of the chapter by Nyman in this volume as the darkest little cloud midway between the southern end of the Coalsack and IC 2948; also see Panorama #6 in the introductory chapter by Mellinger in Volume I). It is located at α2000 12:01:44 δ2000 –65:09.1 (l = 297.7◦, b = –2.7◦). Subsequently it was labeled BHR 71 in the catalog of southern Bok globules by Bourke, Hyland, & Robinson (1995), who noted its association with the embedded source IRAS 11590–6452. The cloud is listed as TGU 1840 in the cloud atlas of Dobashi et al. (2005). Because of its apparent association with the Coalsack, a distance of 200 pc has been used in all studies of BHR 71, although the most recent studies of the Coalsack favor a distance closer to 150 pc (see the chapter by Nyman in this volume). In a major study of BHR 71, Bourke et al. (1997) observed the globule in CO, 13 18 CO, and C O, as well as NH3, and determined a globule mass of about 40 M⊙. The CO maps revealed a highly collimated molecular outflow, with lobes of 0.3 pc extending in opposite directions oriented almost north-south. The data are well modeled by a biconical outflow with a semi-opening angle of 15◦ and an angle to the line-of-sight of approximately 80◦-85◦. The driving source of this outflow is IRAS 11590–6452, a Class 0 source with a bolometric luminosity of ∼9 L⊙. The blue outflow lobe is flowing through a conical cavity seen in both optical (Figure 5) and infrared (Figure 6) images (Bourke et al. 1993, 1997). 7

Figure 5. An optical image of the Bok globule BHR 71 obtained at the VLT. The FOV is about 7′ × 7′, with north up and east left. Courtesy Joao Alves.

Figure 6. BHR 71 as seen by the Spitzer Space Telescope. Left: Blue is 3.6 µm, green is 4.5 µm, and red is 8.0 µm. Right: The Spitzer image combined with the optical image of Figure 5. Courtesy NASA/JPL-Caltech/T. Bourke/c2d Legacy Team. 8

Corporon & Reipurth (1997) discovered two groups of Herbig-Haro knots in BHR 71 (see Table 2). HH 320 forms two knots seen against the high extinction region in the center of the globule, whereas HH 321 consists of two knots in the outﬂow cavity of IRAS 11590–6452. Yun et al. (1997) obtained infrared H2 images and found further embedded shocks.

Table 2. Herbig-HaroObjects in the BHR 71 Globule a a Object α2000 δ2000 HH 320 A 120132.2 –650813 HH 320 B 120131.3 –650805 HH 321 A 120136.5 –650933 HH 321 B 120139.2 –651017 a: from Bourke (2001)

Garay et al. (1998) observed BHR 71 in transitions of SiO, CS, CH3OH, and HCO+, finding that the abundances of methanol and silicon monoxide in the outflow lobes are enhanced, compared to typical dark clouds, by factors of up to ∼40 and 350, respectively. This is likely due to shocks in the outflow lobes that cause the evapora- tion of icy grain mantles, releasing large amounts of ice mantle constituents, such as methanol, into the gas phase. Groundbased and ISO observations have revealed not one, but two sources in BHR 71 (Bourke 2001). The two sources have a separation of 17′′, corresponding to 3400 AU at a distance of 200 pc. The brighter source, IRS 1, corresponds to IRAS 11590–6452. Both sources drive molecular outflows and have circumstellar material, but IRS 1 dominates in both respects. IRS 1 drives the major molecular outflow and the HH 321 knots, whereas IRS 2 powers a much weaker outflow as well as the HH 320 knots. In a CO (3-2) map the second, smaller outflow is fully resolved and shown to be bipolar (Parise et al. 2006). Chen et al. (2008) present a 3 mm dust continuum map of BHR 71 which shows that IRS 1 is associated with a strong dust continuum source, whereas only weak emission is detected from IRS 2. Spitzer observations of BHR 71 show the shocked outflows from both sources, see Figure 6.

2.5. CG 12 The reﬂection nebula NGC 5367 was discovered by John Herschel in 1834. A small CO cloud was found at this location by Van Till, Loren, & Davis (1975). A year later, Hawarden & Brand (1976) found that the cloud is an impressive cometary globule, which they named CG 12, with a tail one degree long. It is also known as TGU 1970 (Dobashi et al. 2005), MBM 112 (Magnani, Blitz, & Mundy 1985) and BHR 92 (Bourke, Hyland, & Robinson 1995). It is a relatively high-latitude cloud, located ◦ ◦ at l = 316.5 , b = 21.1 , corresponding to α2000 13:57.6, δ2000 –39:59. Williams et al. (1977) suggested a distance of 630 pc to CG 12, while Maheswar, Manoj, & Bhatt (2004) measured extinction towards stars closer than and beyond the globule, and derived a distance of about 550 pc. With a Galactic latitude of 21◦, CG 12 is located about 200 pc above the Galactic plane, far from other dark clouds or sites of star formation. CG 12 has been observed in various millimeter transitions. White (1993) observed the globule in CO and C18O, and found a well collimated molecular outﬂow. Further detailed and extensive millimeter observations by Haikala et al. (2006) and Haikala & 9

Figure 7. The large cometary globule CG12. From the blue Digitized Sky Survey.

Olberg (2007) showed that the head of CG 12 harbours three dense cores, CG 12N, CG 12S, and CG 12SW, with the molecular outflow coming from CG 12S. This core contains the strong point source IRAS 13547–3944 and, offset from this source, a mm continuum source which is located at the center of the outflow. The northern core contains another source IRAS 13546–3941. The magnetic field of CG 12 has been studied by Marraco & Forte (1978) and Bhatt, Maheswar, & Manoj (2004). CG 12 contains five B and A stars. The two most massive form the visual binary h4636, discovered by John Herschel1 and surrounded by a bright reflection nebula (see Figure 7). The binary has a separation of 3.7 arcsec, the northernmost h4636N is a reddened B4 star (V∼10.7) and h4636S is a B7 star (V∼10.3). Their spectra are very different, the northern showing strong Hα emission, and the southern having no emission lines (Williams et al. 1977). The third B-star is CoD –39◦8583, which has a spectral type of B8, and is also surrounded by a reflection nebula. The two A-stars are sources 6 and 8 of Williams et al. (1977), source 6 is an A4 star and source 8 an A2 star according to Maheswar et al. (2004). Source 8 may be associated with the reflection nebula Bernes 146 (Bernes 1977). This little cluster of stars was first recognized as a group of Hα emission line stars by Williams et al. (1977).

1It is interesting to note that when discovered in 1834, h4636 probably was the ﬁrst pre-main sequence binary ever seen, albeit only recognized as such much later. 10

If one extrapolates a standard IMF from the known intermediate-mass stars, a siz- able population of low-mass young stars is expected. In a major study, Getman et al. (2008) used the Chandra X-ray Observatory to image CG 12 with the ACIS detector, detecting 128 X-ray sources, of which about half are likely to be young stars, mostly lightly obscured T Tauri stars but also including several embedded stars. Using a color- magnitude diagram, Getman et al. estimated ages for the unobscured low-mass population, and found a large age spread, ranging from <1 Myr for several embedded sources to ∼20 Myr. The data are sufficiently uncertain that they are consistent with both a continuous star formation history and with several distinct episodes of star formation. CG 12 has a 10 pc long tail, providing a well defined axis, which suggests that an outside event has led to the cometary morphology of the globule, and at the same time leading to the star formation activity in the globule (Williams et al. 1977). Surprisingly, the head points away from the Galactic plane, suggesting that the energetic event leading to the cometary morphology took place at an even larger height above the Galactic plane. The HI maps of Cleary, Haslam, & Heiles (1979) and Dickey & Lockman (1990) show a complete HI shell with a diameter of approximately 20◦ and centered at about l = 315◦, b = 30◦. CG 12 is close to the edge of this shell and nearly points to its center (Maheswar, Manoj, & Bhatt 2004). A far-infrared shell, GIRL G318+32, is also found here (Könyves et al. 2007). Getman et al. (2008) note that a single supernova explosion cannot create such a huge cavity, while a superbubble produced by many supernovae requires a rich stellar cluster not likely to be found at such a height above the plane. Getman et al. (2008) searched for longer-lived B stars ahead of CG 12 and found half a dozen which appear to be at the right distance, including HD 120958, a B3V star which lies precisely on the rather well defined axis of the cometary globule. They speculate that HD 120958 could be the relic of a massive binary system of which the primary exploded as a supernova. CG 12 is a unique small star forming region, that deserves further studies, which may help to understand its enigmatic origin.

2.6. L43

L43 is a small filamentary cloud in the constellation Ophiuchus located at about α2000 ◦ ◦ 16:34.5, δ2000 –15:47 (l = 1.4 , b = +21.0 ). In the cloud catalog of Dobashi et al. (2005) it is listed as TGU 23. L43 was first studied by Elmegreen & Elmegreen (1979), who mapped it in 12CO and 13CO. They found it to be a thin filament with approximate dimensions of 10′ × 70′, although the region with noticeable extinction is only half of those dimensions. It is interesting to note that the long axis of L43 is parallel to the streamers of the ρ Ophiuchi cloud complex (Figure 3 of Herbst & Warner 1981 gives a good overview of the region). Due to the relative proximity to the Ophiuchus cloud complex, early work assumed a distance of about 160 pc. Subsequently de Geus et al. (1990) performed a CO survey of the dark clouds in Ophiuchus, and argued for an upper limit to the distance of 130 pc, a distance that has been adopted in much recent work. Elmegreen & Elmegreen (1979) noted two nebulous stars in L43, which became listed as RNO 90 (HBC 649, IRAS 16312–1542) and RNO 91 (HBC 650, IRAS 16316– 1540) in the catalog of Cohen (1980). RNO 90 is irregularly variable, and has the two variable star designations V1003 Oph = V2132 Oph. The two stars were subsequently studied by Herbst & Warner (1981), who obtained optical and infrared photometry of both stars, and a spectrum of RNO 90, revealing it to be a rich emission line T Tauri 11 star. Optical spectra of both stars were presented by Levreault (1988). Early far-infrared observations of L43 were obtained by Nordh et al. (1981). A VLA 3.6 cm map of L43 detected four sources, one of which coincides with RNO 91.

Figure 8. The small dark cloud L43 with its two nebulous stars, RNO 90 and RNO 91. The latter drives a major bipolar outﬂow, with the blue lobe to the southeast, and the red lobe to the northwest. North is up and east is left. From Bence et al. (1998).

The reason that L43 has attracted considerable attention goes back to the first major study of the cloud by Mathieu et al. (1988), who discovered a bipolar molecular outflow emanating from RNO 91. CCD images reveal a clear cavity in the cloud with RNO 91 at its apex and with the blue lobe of the outflow fitting between the cavity walls. Their NH3 map shows two dense condensations on either side of RNO 91. The more massive is the one to the east of RNO 91, further mapped in NH3 by Benson & Myers (1989). It has subsequently been detected at 450 and 850 µm by Bence et al. (1998), Shirley et al. (2000), Young et al. (2006) and Wu et al. (2007), and has been dubbed L43-SMM. Its magnetic field has been studied by Ward-Thompson et al. (2000) and Crutcher et al. (2004). The RNO 91 outflow was also mapped by Levreault (1988), Myers et al. (1988), and Parker et al. (1988). In a higher resolution CO J = 2-1 map, Bence et al. (1998) show that the outflow is slow and poorly collimated, and emerging perpendicularly to the long axis of the L43 cloud (see Figure 8). There is no evidence for a Herbig-Haro jet in the RNO 91 cavity, and Bence et al. (1998) argue that the best-fitting outflow model is one of a slowly expanding shell. Very detailed 12 observations of the molecular outflow in CO were obtained at the BIMA 10 antenna interferometer by Lee et al. (2002), which show the cavity in fine detail. These data, augmented with several more transitions, have been analysed by Lee & Ho (2005), who propose a simple kinematic model with a wide-opening base and an expanding cylindrical shell, representing the late stages in the destruction of the cloud core. While no HH objects are known to be associated with RNO 91, there is evidence for shocked molecular hydrogen (Kumar et al. 1999). Based on millimeter continuum data, Terebey et al. (1993) suggested that L43 is surrounded by a circumstellar disk, and André& Montmerle (1994) present disk models for both RNO 90 and 91. In a detailed study, Weintraub et al. (1994) present infrared spectroscopy of the disk around RNO 91, and find spectral features of frozen H2O, CO, and possibly XCN. Further infrared spectra of water ice in RNO 91 are presented by Brooke et al. (1999), and a number of ice features are identified by Boogert et al. (2008) using Spitzer data. The reflection nebula around RNO 91 has been studied by Schild et al. (1989) and Scarrott et al. (1993), both of which demonstrate that all of the nebulosity is reflected light from RNO 91, a result further supported by the infrared polarimetry of Weintraub et al. (1994). Structure in the infrared nebula is visible in the K-band images of Heyer et al. (1999) and Connelley et al. (2007).

2.7. B62 B62 (= L100) is a well defined globule in Ophiuchus that forms part of the disturbed cloud region east of ρ Ophiuchi and north of B59. It is located at α2000 17:15.9 δ2000 –20:56 (l = 3.1◦, b = +10.0◦). Since the globule was discovered by Barnard (1919) (see Figure 5 in the chapter by Alves, Lombardi, & Lada in this volume) it was paid no attention until Cohen (1980) noted the presence of two faint nebulous stars, RNO 92 and 93, towards the globule. In a subsequent study, Reipurth & Gee (1986) found four Hα emission stars, including RNO 92/93, and most recently Reipurth et al. (2008) found a fifth faint Hα emission star in the globule. Coordinates for these 5 stars are given in Table 3. Whereas B62-Hα 1, 2, 3, and 5 are projected towards the dense globule and are associated with reflection nebulae, B62-Hα4 is located well above the globule towards the northeast. Plaut (1968) noticed the variability of B62-Hα3, leading to its inclusion in the GCVS as V1725 Oph. B62-Hα1 was found by Reipurth & Gee (1986) to be a visual binary with a separation of 4.4 arcsec. It was observed in the near-infrared by Chelli et al. (1995), who found the companion to dominate the system at L-band.

Table 3. Hα emission stars in the B62 globule a Star α2000 δ2000 SpT Other ID’s B62-Hα1 171555.7 –205603 M0 RNO92,HBC658 B62-Hα2 171611.7 –205755 M2 HBC659 B62-Hα3 171613.8 –205746 M0.5 RNO93,HBC661,V1725Oph B62-Hα4 171613.1 –205429 M3 HBC660 B62-Hα5 171611.0 –205738 a: from Reipurth & Gee (1986) 13

The embedded source IRAS 17130–2053 is located towards the center of the globule (Reipurth & Gee 1986), see Figure 10, and is associated with an ammonia core (Anglada et al. 1997). A molecular outflow centered on this source was detected by Parker et al. (1988). In a subsequent study, Reipurth et al. (2008) have found this source to be driving a bipolar Herbig-Haro flow, HH 1000, with a series of bow shocks, visible in the deep Hα image in Figure 9. The image shows that B62 has a flattened appearance with HH 1000 breaking out perpendicularly to the major axis of the globule through a cone-shaped cavity. Another bipolar HH flow, HH 1001, lies along an ENE-WSW axis and is centered on B62-Hα1. To the south, the diffuse outskirts of B62 is illuminated by the bright late A-star BD –20◦4896. The reflection nebula is known as vdB 110 (van den Bergh 1966).

Figure 9. The Bok globule B62. The five Hα emission stars B62-Hα1-5 are labeled. The embedded source in the middle of the globule, IRAS 17130–2053, is powering a bipolar Herbig-Haro flow, HH 1000, perpendicular to the main axis of the globule. The young binary B62-Hα1 drives another bipolar Herbig-Haro flow, HH 1001, towards ENE and WSW. The bright star BD−20◦4896, an interloper, is illuminating the globule from beneath the edge of the image. The field of view is about 7′ × 9′, and north is up and east is left. Image obtained through an Hα filter at the 8m Subaru telescope. From Reipurth et al., in preparation. 14

Figure 10. The B62 globule seen in a JHK color mosaic from 2MASS data. The ﬁeld is the same as in Figure 9. The IRAS 17130–2053 source that drives the HH 1000 outﬂow is seen at the center of the globule. Courtesy Colin Aspin.

There is no evidence that the star is young, and it may well be just accidentally passing through the tenuous envelope of the globule. Using Str¨omgren photometry of the star and assuming that the star is of luminosity class V, Reipurth & Gee (1986) estimated a distance to BD–20◦4896, and thus to B62, of 225 ±25 pc. Just north of B62 is the cometary globule B61 (L111), which is smaller but also highly opaque (Reipurth & Gee 1986). The bright rim is facing towards the only O-star in the vicinity, the O9.5 V runaway star ζ Oph that is moving away from the Sco-Cen association (see the chapter by Preibisch and Mamajek in this volume).

2.8. B92 and B93 Barnard (1913) drew attention to two small markings within the rich star clouds of Sagittarius. They later received the identiﬁcations B92 and B93 in his catalog of dark clouds (Barnard 1919). These objects were among those that Barnard singled out in his arguments that the dark clouds were real objects, and not just voids of stars. Figure 11 shows the two objects as seen on the Digitized Sky Survey, B92 (aka L323, TGU 135, CB 125) is the larger (approximately 15′ × 9′) cloud to the west, and B93 is the smaller cometary cloud to the east. The two clouds are located just north of the large L291 cloud and are projected against the rich patch of the Milky Way known as M24, or popularly as the “Sagittarius Star Cloud” (see also Figure 1 of the chapter by Reipurth, Rodney, & Heathcote in this volume). The cloud coordinates for B92 are α2000 18:15.5, ◦ δ2000 –18:11 (l = 12.7 , b = –0.6) and for B93 they are α2000 18:16.9, δ2000 –18:04 (l = 13.0◦, b = –0.8). There is some confusion in the literature about the Lynds designation of B93. SIMBAD lists it as L327, but many authors refer to it as L328. When plotting the coordinates on the DSS, L328 corresponds to the dense head of the globule, and L327 to the tenuous tail. The preferred nomenclature should be B93, but when a Lynds number is used, preference should be given to L328. 15

Figure 11. The two Bok globules B92 and B93. B92 is the larger cloud (about 9′×15′) to the west, and B93 is the smaller cometary cloud to the east. From the Digitized Sky Survey. North is up and east is left. Coordinates are for J2000.

Figure 12. The Bok globule B92 as seen on a red ESO Schmidt plate from the Digitized Sky Survey. The young star B92-IRS is indicated. The ﬁeld is 15′ × 15′. 16

Bok & McCarthy (1974) adopted a distance of 200 pc for B92, because of the absence of many foreground stars to the globule and because of its relative proximity to the Ophiuchus clouds. This distance has been used in many later studies, but is obviously little more than an educated guess. Stellar luminosities derived on the basis of this distance should be viewed with considerable caution. Various surveys have been made in search of young stars in B92 and B93. Ogura & Hidayat (1985) searched both globules for Hα emission stars, but did not ﬁnd any. Clemens & Barvainis (1988) listed a number of IRAS sources found in the general direction of B92 (their object CB 125), but none are likely to be related to the globule. 18 A map of B92 in C O and NH3 by Lemme et al. (1996) show several cores. Deep CCD-images of B92 have revealed a faint nebulous star near the center of B92 and located at the edge of an elongated cavity through which background stars can be seen (Reipurth, unpublished). This object, B92-IRS, is marked in Figure 12, it is presumably a young star that through outﬂow activity has blown the cavity seen in the globule. The star is located at α2000 18:15:36.1, δ2000 –18:12:11.

Figure 13. The Bok globule B93 = L328 contains a small cluster of cold dust cores as seen in this 350 µm SHARC-II map obtained by Wu et al. (2007). The core L328-SMM2 may contain a very low luminosity protostar.

B93 has been observed at 450 and 850 µm with SCUBA on JCMT by Visser et al. (2001, 2002), who found a cold core in the center of the dense head of B93. Their 5-point map in 12CO J=2-1 did not reveal any outﬂow. Wu et al. (2007) observed the globule at 350 µm and found three cold condensations (see Figure 13), of which Spitzer observations indicate that SMM2 may possibly contain a very low-luminosity protostar.

2.9. L483 The small L483 cloud is located towards the Aquila Rift at Galactic coordinates l = 24.9◦, b = +5.4◦, and it is widely assumed that it is associated with the Rift at a distance of ∼200 pc (Dame & Thaddeus 1985). It forms a dense core in a small cloud that is labeled TGU 259 in the cloud atlas of Dobashi et al. (2005), and that also encompasses the Lynds clouds 475, 476, 477, 479, and 482 (Figure 14). 17

Figure 14. The small cloud L483 is located in the Aquila Rift. The ﬁgure shows an excerpt from the extinction atlas by Dobashi et al. (2005), the abscissa is Galactic longitude from 21◦ to 30◦ and the ordinate is Galactic latitude from +1◦ to +10◦.

L483 contains the source IRAS 18148–0440, which was first identified as an embedded young object by Parker (1988), and its very red colors compared to many other embedded sources were subsequently recognized (Parker 1991, Ladd et al. 1991a). A prominent molecular outflow was discovered by Parker et al. (1991). A thermal radio continuum source has been detected towards IRAS 18148–0440 at α2000 18:17:29.87 δ2000 –4:39:38.8 (Beltrán et al. 2001). The source has a luminosity of about 10 L⊙ (Fuller et al. 1995), and its energy distribution indicates that it is a Class 0 source (Fuller et al. 1995, Fuller & Wootten 2000) although it appears to be in transition towards a Class I source (Tafalla et al. 2000, Pezzuto et al. 2002). The source is located in a dense core detected in ammonia by Fuller & Myers (1993) and Anglada et al. (1997), and mapped at higher resolution with the VLA by Fuller & Wootten (2000). The core has been mapped in other transitions by Tafalla et al. (2000). Maps of the circumstellar envelope in the submillimeter lines of CS (J = 7-6) and HCN (J = 4-3) obtained at the ASTE telescope are presented by Takakuwa et al. (2007), which show that warm gas (>40 K) is present as much as 4000 AU from the source. Using the BIMA interferometer, Park et al. (2000) mapped the distribution of C3H2 212–101 and found an extended envelope with a size of ∼3000 × 2000 AU. Jørgensen (2004) presented a millimeter-wavelength aperture synthesis study of the envelope in 8 molecular species using the OVRO Millimeter Array and found evidence for chemical differenti- ation around the source. Dense material close to the central protostar shows a velocity gradient perpendicular to the outflow axis, consistent with rotation around a ∼1 M⊙ central object. 18

Figure 15. The source IRAS 18148–0440 is embedded in the small cloud L483 and drives a ﬁnely collimated molecular outﬂow, see here in an integrated intensity map of 12CO 4-3. The upper panel shows redshifted emission, and the lower panel blueshifted emission. The VLA position of the source is marked by a star. Crosses and circles mark positions where 12CO 2-1 and 13CO 2-1 spectra were taken, respectively. Strong H2 emission is found at the location of the square with an arrow. From Hatchell et al. (1999).

Early far-infrared and submillimeter maps of the L483 source were presented by Ladd et al. (1991b), who found the emission to be extended. The source has subsequently been mapped repeatedly with SCUBA at 450 and 850 µm (e.g. Fuller & Wootten 2000, Shirley et al. 2000, Visser et al. 2002). The dust continuum emission is extended, principally in the northeast to southwest direction. Shirley et al. (2002) used a one-dimensional radiative transfer code to model these maps, and found that the dust continuum emission is best fitted by a shallow (p = 1.2) power law. The internal luminosity of the model is 13 L⊙, making the contribution from the interstellar radiation field negligible in comparison. Jørgensen et al. (2002) also used a one-dimensional radiative transfer code to model the envelope of the L483 source, and also found a best fit with a shallow power law. Jørgensen (2004) obtained continuum emission maps at 2.7-3.4 mm with the OVRO Millimeter Array, and found the data to be well fitted by an extended envelope model without introducing a disk or compact source. Indications of gravitational infall in IRAS 18148–0440 was noted in high resolution line studies by Myers et al. (1995), Mardones et al. (1997), Park et al. (1999), Fuller & Wootten (2000), and Tafalla et al. (2000). 19

Figure 16. The bipolar reﬂection nebula around IRAS 18148–0440 in L483 is seen in this K-band image. The source is located in the highly obscured region between the two lobes. The ﬁeld is approximately 50′′ × 70′′, with north up and east left. From Connelley et al. (2008).

The molecular outflow discovered by Parker et al. (1991) extends along an east- west line. It was further mapped in CO J = 3-2 by Fuller et al. (1995), in CO J = 2-1 by Bontemps et al. (1996), and in CO J = 4-3 by Hatchell et al. (1999), see Figure 15. Additional multiple transitions were mapped by Tafalla et al. (2000). BIMA interferometric observations of HCO+ 1-0 by Park et al. (2000) show that the outflow is clumpy, and the opening angle is widest for the slowest moving material. The multi- transition study by Jørgensen (2004) using the OVRO Millimeter Array suggests a clear interaction between the outflowing gas and the quiescent core. The innermost region of the outflow was mapped with the SMA in CO J = 2-1 and other transitions (Jørgensen et al. 2007). Carolan et al. (2008) modeled line profiles of four CO isotopomers towards the L483 source in an attempt to probe the distinct physical conditions in the different components, core, envelope, and outflow. A bipolar reflection nebula is seen on K-band images, along the same axis as the molecular outflow (Hodapp 1994, Fuller et al. 1995, Connelley et al. 2007). The western part is more prominent (Figure 16) and coincides with the blue outflow lobe. The reflection nebula is highly variable and has been monitored by Connelley et al. (2008). A bipolar molecular hydrogen jet, with the principal lobe aligned with the brightest lobe of the reflection nebula, was discovered by Fuller et al. (1995) and further imaged by Connelley et al. (2008). The jet bow shock was studied with long slit spectroscopy of the infrared H2 lines by Buckle et al. (1999), who suggested that it is a C-shock with shock velocity of 40-45 km sec−1. An H2O maser is found in association with the embedded source (Wilking et al. 1994, Xiang & Turner 1995, Claussen et al. 1996, and Furuya et al. 2003). 20

2.10. L723

L723 is a small, rather isolated cloud in the constellation Sagitta, just north of Aquila, ◦ ◦ located at α2000 19:17.9, δ2000 +19:12.3 (l = 53.0 , b = +3.0 ). Attention was first drawn to this region when Frerking & Langer (1982) carried out a 12CO survey of 180 Lynds clouds of opacity classes 5 and 6 in search of high velocity line wings; L723 was one of four regions identified. Goldsmith et al. (1984) plotted reddening vs distance towards and around the L723 cloud and derived a distance of 300±150 pc, which has been adopted in subsequent studies. Based on a 12CO J=1-0 map towards L723, Goldsmith et al. (1984) found a molecular outflow with well separated lobes and evidence that two separate outflows are present, a major one oriented east-west, and a smaller one directed north-south. Subse- quent maps in several millimeter transitions with increasing resolution led to a debate whether there are two almost orthogonal outflows, or a single one with either a wide opening angle or a precessing outflow axis (Moriarty-Schieven & Snell 1989, Avery et al. 1990, Hayashi et al. 1991, Hirano et al. 1998). In a high resolution CO study made with the BIMA interferometer, Lee et al. (2002) obtained a very detailed outflow map (see Figure 17, which strongly supports the two-flow scenario. Vrba et al. (1986) discovered two Herbig-Haro knots, which are now known as HH 223. Both are associated with the blueshifted lobe of the main east-west outflow. A more detailed Hα and [SII] imaging study was made by López et al. (2006), who found further knots of HH 223 along the axis of the principal outflow, see Figure 18. (Note that Hirano et al. 1998 erroneously refer to some of the knots of Vrba et al. (1986) as HH 82 and 84). Further knots are seen in the infrared (Hodapp 1994, Palacios & Eiroa 1999). The embedded source IRAS 19156+1906 is located at the center of the two outflows (Davidson 1987). It is a Class 0 source with a luminosity of about 3 L⊙ at the assumed distance of 300 pc. Anglada et al. (1991) used the VLA at 3.6 cm to discover two radio continuum sources at the center of the outflows, with a separation of 15′′. In a higher resolution follow-up study, Anglada et al. (1996) noted major differences between the two sources. While VLA 1 is unresolved at the 0.3′′ resolution employed, VLA 2 shows a fine bipolar thermal jet along the axis of the principal molecular outflow, clearly supporting the identification of VLA 2 as the driving source. Dartois et al. (2005) used the IRS low resolution spectrometer onboard Spitzer to find a very large CO2 ice column density toward the embedded source. It is not clear that VLA 1 is driving the smaller N-S oriented flow, because a) the source is not detected in the 1.3 mm dust continuum in contrast to VLA 2 (Cabrit & André1991, Reipurth et al. 1993); b) VLA 1 is located outside the dense ammonia gas surrounding VLA 2 detected by Girart et al. (1997); and c) the spectral index of VLA 1 is suggestive of a non-thermal source (Anglada et al. 1996). It appears that another source is required to drive the smaller N-S outflow. Indirect evidence for possibly another source in the region was found in the form of an H2O maser discovered by Girart et al. (1997) and further observed by Furuya et al. (2003). Firm evidence has come with a detailed, high resolution radio continuum study by Carrasco-González et al. (2008), who found a small cluster of sources at the location of IRAS 19156+1906. First, they discovered that VLA 2 is a close binary with a separation of 0.3′′ between the components 2A and 2B. Second, they found that a separate source, 2C, is associated with the H2O maser. Finally they found that yet another source a few arcseconds to the ESE is associated with a new millimeter con- 21

Figure 17. The region around L723 VLA2 in CO J = 1-0 emission superposed ′′ ′′ on an H2 image. The beam size is 8 × 8 . The dotted line outlines the observed region. From Lee et al. (2002).

Figure18. AnHα CCD image of the center of the L723 cloud with the HH 223 flow extended ESE to WNW. The two sources VLA 1 and VLA 2 are marked, as are several stars or knots (marked with V) noted by Vrba et al. (1986). From López et al. (2006). 22 tinuum source. Altogether, it appears that VLA 2 constitutes a small newborn multiple system, from which the two large molecular outflows emanate.

2.11. B335 The Bok globule Barnard 335 (also known as L663 or CB 199) is located in Aquila (see the chapter by Prato, Rice, & Dame in Volume I) at α2000 19:36:55, δ2000 +07:34.4 (l = 44.9◦, b = –6.5◦). It is a prototypical Bok globule, a tiny dark cloud with a completely opaque core approximately 2 × 3 arcmin along E-W and N-S directions (Figure 19). Bok & McCarthy (1974) estimated an upper limit to its distance of 400 pc from the lack of foreground stars towards the core. Tomita et al. (1979) suggested a distance of 250 pc derived from star counts, a value supported by Frerking et al. (1987), who suggests a connection with the Lindblad ring. All later studies have adopted a distance of 250 pc. At this distance the globule has a diameter of about 0.2 pc. Harvey et al. (2001) noted that they would get a better fit to their color excess data if the globule had a smaller distance. In a re-examination of the available photometry of stars in the direction of the globule, Stutz et al. (2008) argue that a distance of 150 pc, with an uncertainty of nearly a factor two, is more appropriate. B335 has attracted much attention following the discovery of an embedded far- infrared source. Initially the far-infrared flux was ascribed to re-emission of the interstellar radiation field (Keene at al. 1980) until the compact nature of the emission was recognized (Keene et al. 1983). After the launch of the IRAS satellite this source be- 2 came known as IRAS 19345+0727. The source has low luminosity, L ≈ 3 (D/250) L⊙ (e.g., Shirley et al. 2000), and no near-infrared counterpart has been detected (Hodapp 1998). Stutz et al. (2008) combined Spitzer IRAC and MIPS photometry of the source with existing longer-wavelength data and agree with the abovementioned luminosity estimate, but note that the luminosity is 1.2 L⊙ at their preferred distance of 150 pc. Gee et al. (1985) detected the source at sub-millimeter wavelengths, and argued that the object could be a protostar. Andréet al. (1993) classified the source as a Class 0 object. Further submillimeter continuum observations were presented by Chandler et al. (1990), who resolved the continuum source in the N-S direction in a 8′′ beam, but not along an E-W line. The source was detected in the 3.6 cm radio continuum by Anglada et al. (1992, 1998). Further 3.6 cm flux measurements indicate that the source shows considerable variability (Avila, Rodr´ıguez, & Curiel 2001, Reipurth et al. 2002). Far-infrared spectroscopy of the source is reported by Nisini et al. (1999). IRAS 19345+0727 drives a bipolar molecular outflow oriented east-west, and first detected and studied by Frerking & Langer (1982) and Goldsmith et al. (1984). The flow is well collimated, with a total length-to-width ratio of ∼ 5. It moves very close to the plane of the sky, with an inclination of only 5-10 degrees, such that the blue-shifted and red-shifted lobes are well separated. The eastern lobe is 0.9 pc long and tilted towards us, while the western lobe is 0.4 pc long and tilted away from us (Cabrit et al. 1988, Hirano et al. 1988,1992, Moriarty-Schieven & Snell 1989, Stutz et al. 2008). Aperture synthesis maps of 13CO,C18O J = 1-0, and 2.7 mm continuum emission show high-velocity emission perpendicular to a dense core that is elongated north-south but unresolved along the outflow axis (Chandler & Sargent 1993). Vrba et al. (1986) and Reipurth, Heathcote, & Vrba (1992) discovered a chain of three little HH objects, HH 119, located on an east-west line and comprising a tightly collimated string of optical emission knots emanating from the embedded driving source. HH 119A,B is in the western red lobe of the associated molecular outflow 23

Figure 19. B335 as seen in a color composite based on Hα (red), [SII] (green, and R band (blue) images. Components of the bipolar Herbig-Haro flow HH 119 are labeled, and several have proper motion vectors indicated. The vector for knot F is displaced to fit inside the figure. Red contours show a bipolar reflection nebula as imaged at 8 µm with Spitzer, and yellow contours show the location of the source at 24 µm. The field of view is about 5 × 4 arcmin, and North is up and east is left. From Gaalfalk & Olofsson (2007).

and HH 119C in the eastern blue lobe, and proper motions are in opposite directions away from the source (Reipurth, Heathcote, & Vrba 1992). Gaalfalk & Olofsson (2007) confirmed and improved these proper motions and discovered further optical and infrared components of the HH 119 bipolar flow. ISO-LWS spectra were obtained of the main HH 119 knots by Nisini et al. (1999). An H2O maser has been studied by, e.g., Claussen et al. (1996). Despite its simple optical morphology, B335 shows considerable structure at millimeter wavelengths. It is centrally condensed, with the center of the globule corre- 18 + sponding to peaks in the distribution of CS, NH3,C O,H2CO and HCO (e.g., Mar- tin & Barrett 1978, Snell et al. 1982, Menten et al. 1984, Walmsley & Menten 1987, Zhou et al. 1990, Hasegawa et al. 1991, Velusamy, Kuiper, & Langer 1995, Murphy, Little, & Kelly 1998, Saito et al. 1999, Choi 2007, Takakuwa et al. 2007, and Stutz et al. 2008). Zhou et al. (1993) observed five rotational transitions of H2CO and CS toward B335 with high spatial and spectral resolution, and found direct, kinematic ev- 24 idence of collapse motions in the globule as predicted in the inside-out collapse model of Shu (1977). Zhou (1995) and Choi et al. (1995) calculated theoretical line profiles of collapsing cores for comparison with the data for B335. Interferometric observations of CS J = 5-4 emission by Wilner et al. (2000) do not show dense gas with infall velocities approaching 1 km s−1 at 600 AU scales as predicted by the inside-out collapse models, but the authors note that additional species and transitions should be observed at similarly high resolution to address possible issues by abundance and/or excitation effects. Harvey et al. (2001) used deep HST/NICMOS and Keck near-infrared images to probe the structure of B335 using star counts. They find that the radial profile of the reddening is well fitted by the inside-out collapse model, but note that an unsta- ble Bonnor-Ebert sphere provides an equally good fit over the radii that the extinction data probe. The data show strong evidence for a bipolar conical outflow cavity with a semi-opening angle of 41◦±2◦. In subsequent studies, Harvey et al. (2003a, 2003b) presented subarcsecond-resolution observations from the IRAM PdB Interferometer in the dust continuum at 1.2 and 3.0 mm. The observations probe the innermost regions on scales of less than 100 AU, and reveal a compact structure around the source that appears to be a circumstellar disk with radius less than 100 AU. The density structure of the B335 core indicates an r−1.5 inner region in gravitational free fall surrounded by an r−2 envelope. Frerking et al. (1987) determined the mass of the globule to be 11-14 M⊙, and found it to be associated with a tail of tenuous gas of dimensions 20′ × 36′, having an additional mass of about 25 M⊙ and containing several minor condensations. This morphology is very reminiscent of the cometary globules studied by Reipurth (1983), and suggests that B335 was once affected by the radiation from a massive star, or possibly a supernova. The direction of the tail indicates that such a massive star should have been located to the WSW of B335. Because of its structural simplicity and lack of source confusion, B335 is an ex- cellent target for studying the chemistry of a protostellar region. Evans et al. (2005) have obtained observations of 25 transitions of nine molecules which they compare to models of chemical abundances, where the temperatures of dust and gas are calculated from the luminosity of the protostar and the density distribution. Optical polarization measurements of background stars viewed through the periph- ery of the globule have been reported by Vrba et al. (1986), who find the polarization vectors to lie along position angle 111◦±4◦, close, but not equal, to the position angle of the molecular outflow, which is about 90◦. Hodapp (1987) obtained I-band polarimetry of a larger number of stars, and found a complex distribution of polarization that varies across B335.

2.12. L810 ◦ L810 is a small cloud in Vulpecula located at α2000 19:45:24, δ2000 +27:51.0 (l = 63.6 , b = 1.7◦). It is also known as CB 205 (Clemens & Barvainis 1988) or Khavtassi 657 (Khavtassi 1955). It is a fairly round cloud with a diameter of about 6 arcmin (e.g. Bok 1977, Bok & Cordwell 1973). Its distance has been estimated in a number of studies. Herbst & Turner (1976) used star counts to determine a distance of 1.5 - 2.0 kpc, Neckel et al. (1985) used radio data to suggest a distance of 1.5±0.5 kpc, Turner (1986a) used star counts to derive a distance of 2.5±0.2 kpc, and Neckel & Staude (1990) used photometry of foreground stars to suggest a distance of 2.0±0.3 kpc. See also the 25

Figure 20. The small cloud L810 as seen on the blue Digitized Sky Survey.

Figure 21. The small cloud L810 as observed at 850 µm. The ellipse indicates the IRAS 19433+2743 source, filled squares are bright NIR sources, and the filled triangle is an H2O maser. From Codella et al. (2006). 26 discussion in Hilton & Lahulla (1995). Turner (1986a) and Xie & Goldsmith (1990) noted that L810 is likely to be a member of the Vul OB1 association, which is located at about 2.3 kpc (e.g. Turner 1981), and further noted that it is one of a group of cometary dark clouds with similar radial velocities and heads pointing toward the center of Vul OB1 (see also Figure 3 of Turner 1986a). Subsequent authors have adopted either a distance of 2.0 or 2.5 kpc. At such a large distance, L810 can hardly be classified as a globule, but rather must be considered a small cloud. Herbst & Turner (1976) noted that at least one star towards L810 is surrounded by a reflection nebula (Figure 20). Neckel et al. (1985) used millimeter observations to detect a warm NH3 core towards the center of L810, associated with a nebulous star (their no. 7) that is also a bright near-infrared source. Turner (1986b) noted that star 7 has varied by at least 2 magnitudes. In a follow-up study, Neckel & Staude (1990) found that star 7 and three other stars may have Hα emission, and suggested that a dozen stars could be associated with the cloud. Scarrott et al. (1991) obtained a polarization map of L810 and showed that star 7 is not the illuminator of the reflection nebula, which they instead attribute to an embedded source, L810-IRS, and they questioned the suggestion by Neckel & Staude that many young stars are illuminating the globule. In a near-infrared study of L810, Yun et al. (1993) detected the illuminating source L810-IRS which they identify with IRAS 19433+2743, the only IRAS source within the optical core of L810. Xie & Goldsmith (1990) found a bipolar molecular outflow, which was further mapped by Yun & Clemens (1994) and Clemens et al. (1996), who found that the outflow is offset by about 30′′ to the west from the IRAS position. Massi et al. (2004) searched for infrared shocked emission in L810, but did not detect any, indicating that early suggestions that a major jet is present in L810 are incorrect. Huard et al. (2000) presented 450 µm and 850 µm of L810, and found a clumpy ring-like structure of cool dust, with two principal sources, SMM 1 and SMM 2. SMM 1 is a bright extended submillimeter source broadly coincident with IRAS 19433+2743, with L810-IRS, and with star 7. SMM 2 is fainter, located about 45′′ southwest of SMM 1, and no optical or near-infrared sources are found in this direction, suggesting that SMM 2 may be a Class 0 source. An H2O maser found by Neckel et al. (1985) is located close to SMM 2. Codella et al. (2006) also observed L810 at 450 µm and 850 µm, and found two more, fainter submillimeter sources, SMM 3 and SMM 4 (see Figure 21), and noted that SMM 1 consists of two sources. They additionally mapped the region in CO (3-2) and noted that several molecular outflows appear to be present, with a complex distribution of high-velocity gas mostly towards the SMM 2, 3, and 4 region. Yun et al. (1996) and Moreira et al. (1997) found three VLA radio continuum sources towards L810, but their nature and association with the submm sources are unclear.

Acknowledgements. I am thankful to the referee, Tyler Bourke, for a critical reading and helpful comments. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and of NASA’s Astrophysics Data System Bib- liographic Services. BR was supported in part by the NASA Astrobiology Institute under Cooperative Agreement No. NNA04CC08A and by the NSF through grants AST-0507784 and AST-0407005. 27

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