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SIMBA Observations of the R Corona Australis Molecular Cloud?,?? A&A 409, 235–244 (2003) Astronomy DOI: 10.1051/0004-6361:20031115 & c ESO 2003 Astrophysics SIMBA observations of the R Corona Australis molecular cloud?;?? R. Chini1,K.K¨ampgen1;2,B.Reipurth2, M. Albrecht1,E.Kreysa3,R.Lemke1,M.Nielbock4, L. A. Reichertz3,A.Sievers5,andR.Zylka6 1 Astronomisches Institut der Ruhr-Universit¨at Bochum, Universit¨atsstrasse 150, 44780 Bochum, Germany 2 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 3 Max Planck Institut f¨ur Radioastronomie, Auf dem H¨ugel 69, 53121 Bonn, Germany 4 SEST, European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile 5 IRAM, Avda. Divina Pastora 7, Nucleo Central, 18012 Granada, Spain 6 I. Physikalisches Institut, Universit¨at zu K¨oln, Z¨ulpicher Strasse 77, 50937 K¨oln, Germany Received 10 March 2003 / Accepted 16 July 2003 Abstract. We have mapped the R Corona Australis molecular cloud at 1.2 mm with SIMBA on SEST and detected 25 distinct dust emission peaks. While 7 of them coincide with positions of previously known young stars, 18 are seemingly not associated with any known stellar object. We discuss the nature of individual sources and conclude that there are at least four small concentrations of young objects located along the filamentary shaped cloud. A comparison with C18O data hints at the depletion of molecules in some of the cores. Our new results yield some conflicting arguments about whether star formation proceeds from north-west to south-east in the R Cr A cloud. Key words. ISM: dust, extinction – stars: circumstellar matter – stars: formation 1. Introduction counts (e.g. Rossano 1978; Andreazza & Vilas-Boas 1996; Cambr´esy 1999), reveal a cometary shaped cloud complex For more than a century, attention has been drawn to a high ex- oriented northwest-southeast which is about 6◦ long with the tinction region in Corona Australis where a number of variable abovementioned young stars located in the dense cometary stars are located. The R Corona Australis cloud coincides with head. This morphology suggests that star formation in the Rossano’s (1978) cloud A and is named after the highly vari- Corona Australis complex has been triggered by an external able Herbig Ae/Be star R Cr A (e.g. Joy 1945; Herbig 1960) influence which possibly originates in the Upper Centaurus- which is surrounded by a bright reflection nebula that also Lupus association (Harju et al. 1993). At a distance of varies with time (e.g. Graham & Phillips 1987). A major reflec- about 170 pc (Knude & Høg 1998), the Cr A cloud complex tion nebula surrounds the B8 star TY Cr A which is an eclips- is among the closest star-forming regions. ing PMS binary (e.g. Vaz 2001) and the neighbouring A0 star HD 176386. The two bright variable stars S Cr A and VV Cr A Surveys of the R Cr A cloud have revealed a population are both T Tauri stars and visual PMS binaries (e.g. Reipurth & of young, visible low-mass stars, either through the presence Zinnecker 1993). of Hα emission (e.g. Knacke et al. 1973; Marraco & Rydgren These young stars are associated with a large complex 1981) or as X-ray sources (e.g. Koyama et al. 1996; Neuh¨auser of dark clouds mapped in molecular and atomic transitions et al. 2000). Infrared surveys have uncovered a small clus- by, among others, Loren (1979), Cappa de Nicolau & P¨oppel ter, named the Coronet, of low-luminosity sources embedded (1991), Harju et al. (1993) and Yonekura et al. (1999). These around R Cr A (Taylor & Storey 1984; Wilking et al. 1986; data, together with large-scale extinction maps based on star Wilking et al. 1997). More deeply embedded sources have been identified through radio continuum observations (Brown 1987; Send offprint requests to: R. Chini, Suters et al. 1996; Harju et al. 2001) and millimetre contin- e-mail: [email protected] uum observations (Reipurth et al. 1993; Henning et al. 1994; ? Based on observations collected at the European Southern Saraceno et al. 1996). These young stars drive various outflows Observatory, La Silla, Chile. which are observed either as Herbig-Haro objects or as molec- ?? Appendices A and B are only available in electronic form at ular outflows (e.g. Hartigan & Graham 1987; Levreault 1988; http://www.edpsciences.org Graham 1993; Anderson et al. 1997). Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20031115 236 R. Chini et al.: SIMBA observations of the R Corona Australis molecular cloud Fig. 1. The complete 1.2 mm mosaic of the R Cr A dark cloud consisting of 71 individual fastscanning maps. This and all the following figures containing SIMBA data are slightly Gaussian smoothed (2800 vs. a beam of 2400 ). The smoothed beam (2800) is indicated in the box to the lower right. The typical 1σ rms noise is 17 1mJy/beam; along the edges, the noise level is obviously higher. The contour lines start at 51 mJy/beam ± (=3 rms). Details of this mosaic are given in subsequent figures. In this paper, we present the first deep, large-scale survey measurements. Maps of Uranus were taken for calibration pur- of the R Corona Australis cloud at millimetre continuum wave- poses. A calibration accuracy of 15% was obtained. All data lengths. Our 1.2 mm maps reveal several small clusters of em- were reduced and analysed with MOPSI1 according to the in- bedded, very cold objects which we interpret in terms of con- structions of the SIMBA Observer’s Handbook (2002). A de- centrations of newborn low-mass stars. tailed description of the data reduction and the data analysis including the determination of the noise in the mosaic is pre- 2. Observations sented in Appendices A and B, respectively. The 1.2 mm continuum observations were carried out with the 37 channel bolometer array SIMBA (SEST Imaging 3. Results and discussion Bolometer Array) at the SEST (Swedish-ESO Submillimetre In the following section, we present and discuss the data from Telescope) on La Silla, Chile, during the commissioning pe- our 1.2 mm survey. Figure 1 shows the total mosaic of the riods in June, July and October 2001. We performed a mo- R Corona Australis region as covered by SIMBA. Table 1 saic that covers an area extending from north-west to south- summarises those 25 dust emission peaks – labelled “MMS” east of roughly 2000 1000 . The mosaic was constructed 00 × 00 (millimetre source) – which we consider to be bona fide de- by combining 71 individual fastscanning maps (8000 per s) of tections. They were selected according to the following crite- different sizes taken at different hour angles in order to re- ria: i) their S=N ratio is larger than 9 (see Appendix B.1 for duce scanning effects. The total integration time spent on the the definition of the S=N ratio); ii) their extent is larger or area was 978 min. The residual noise in the final co-added equal to the beam size; iii) their reality was checked within mosaic varies by 2 around 17 mJy/beam (rms) across the ± individual maps in order to exclude residuals caused by the region due to different numbers of coverages per area. The direction of fast-scanning. All entries in Table 1 are derived beam size of an individual bolometer channel is 2400 HPBW. from the original, unsmoothed mosaic. As to be seen in the Skydips were performed at least every three hours in or- overview in Fig. 1, there are additional peaks above the 3σ der to determine the atmospheric opacity. The zenith opac- ity values range from 0.160 to 0.364. The positional accuracy 1 MOPSI is a software package for infrared, millimetre and radio was determined to be 200–300 by performing frequent pointing data reduction developed and constantly upgraded by R. Zylka. R. Chini et al.: SIMBA observations of the R Corona Australis molecular cloud 237 Table 1. Source positions, peak intensities, morphology, flux densities and other designations for 25 mm sources detected by SIMBA. RCrA RA Dec I (1) Source size (a b)(2) S (3) Other designations 1:2mm × 1:2mm MMS (J2000) [mJy/beam] [00][mJy] h m s 11901 08:3 36◦5701900 260 (0) 25 25 290 S Cr A; ISO 116 h m s − × 21901 04:2 36◦5402300 140 h m s − 31901 06:6 36◦5402500 160 h m s − 41901 09:0 36◦5401800 138 h m s − 51901 14:6 36◦5400200 141 h m s − 61901 33:2 36◦5303500 268 h m s − 71901 38:1 36◦5400300 322 h m s − 81901 38:2 36◦5303600 336 HD 176386 h m s − 91901 41:7 36◦5802800 660 (0) 36 32 1320 IRS 2; TS 13.1; IRAS 21 h m s − × 10 19 01 45:9 36◦5504800 838 h m s − 11 19 01 46:6 36◦5603000 897 h m s − 12 19 01 49:2 36◦5702200 1173 IRS 5; TS 2.4 h m s − 13 19 01 55:5 36◦5703800 2315 confused; see text h m s − 14 19 01 58:0 37◦0100300 150 h m s − 15 19 02 02:4 37◦0103400 158 h m s − 16 19 02 05:0 37◦0103100 147 h m s − 17 19 02 04:8 37◦0000300 180 h m s − 18 19 02 08:6 37◦0004100 170 h m s − 19 19 02 12:4 36◦5701700 146 h m s − 20 19 02 15:3 37◦0103700 160 h m s − 21 19 02 17:8 37◦0103400 148 h m s − 22 19 02 40:7 37◦0801100 146 h m s − 23 19 02 59:0 37◦0703200 472 (126) 36 31 672 IRAS 18595-3712; IRAS 32c; − × ISO-CrA 182 h m s 24 19 03 06:9 37◦1204700 543 (42) 28 24 584 VV Cr A; IRAS 18597-3717 h m s − × 25 19 03 56:1 37◦1503200 250 − (1) Peak intensity measured above the zero level; the beam size is 2400.
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