arXiv:1005.1943v1 [astro-ph.SR] 11 May 2010 atpriiainfo NASA. from participation an consortia tant Investigator Principal European-led by vided it ftePooeetrAryCmr n Spectrometer Photometr Gri and and (SPIRE; Spectral Camera the Receiver and Array Imaging 2010) al. Photodetector et con Poglitsch the sample (PACS; Krause) of O. P.I. sists (EPoS; –formation” of Phases bevtoso ie fbt ih n o–assa for- star portion low– Phase and Demonstration high– Science both low–mass The of mation. sites of observations 6-2 ) hswvlnt eiei rtclfraccurate col for 2009) al. the critical et in Shetty is (e.g., structure born regime density are and wavelength where temperature environments This the The K). of source cold modeling 2010). 20 for spectrum - al. Planck et the (6 Launhardt of peak the 2009; samples which 2008, a et al. Ward-Thompson Herschel et fragmentatio (e.g., Stutz core evolution phys 2007; understand chemical fundamental and to are collapse, necessary structure parameters density ical and Specific formation. temperature star low-mass the simple in d place relatively the taking are studying These for processes that 1997). ideal cloud. cores objects (e.g., common these star–forming make two larger characteristics Henning or a & star–formation one Launhardt in only embedded have molec- low–mass to 1988; isolated tend They undergoing relatively Barvainis & small, Clemens clouds nearby, are ular globules Bok Introduction 1. coe 2 2018 12, October ⋆ Astrophysics & .Stutz A. eshli nEAsaeosraoywt cec instrumen science with observatory space ESA an is Herschel The epresent We accepted Received; 4 3 omn oeua lu.W n htteclm–vrgddu column–averaged p the and that 244 find CB We of 70 cloud. density MIPS molecular column the forming and map, dust–temperature near-IR the and a model sources, and these for data spectrum these Planck With the of peak the sample 2 asCas0pootradasals oe hc slkl to likely is which core, starless a and 0 Class mass oundniydosblw10 below drops density column 1 oei is it core e words. Key process. star–formation the in participating is ftepootla oei 1 is core protostellar the of 19 i-u-vte France Gif-sur-Yvette, 91191 aoaor I,CEA AIM, Laboratoire EM M 12d NS bevtied ai,6 v el’Ob de Av. 61 Paris, de Observatoire CNRS, du 8112 UMR & LERMA eateto srnm n twr bevtr,Universi Observatory, Steward and Astronomy of Department a-lnkIsiu ¨rAtooi,Koisul1,D-6 K¨onigstuhl 17, f¨ur Astronomie, Max-Planck-Institut Herschel Plrt ta.21)dt oe h aeeghrange wavelength the cover data 2010) al. et (Pilbratt 1 , 2 ∼ .Launhardt R. , uttmeaueo nioae trfrigcloud: star-forming isolated an of Dust–temperature 10 Herschel Herschel lbls–IM niiul(B4)–ifae:IM–(S: d (ISM:) – ISM : – (CB244) individual ISM: – globules . ,adta h e the that and K, 6 urnedTm e rga “Earliest Program Key Time Guaranteed bevtoso h sltd o–assa–omn o gl Bok star–forming low–mass isolated, the of observations / aucitn.ms no. manuscript S-NSUiestPrsDdrt IRFU Diderot, Paris DSM-CNRS-Universit . 1 6 .Linz H. , ffi ± 21 0 ta.21)imaging–mode 2010) al. et n . bevtoso h o lbl CB244 globule Bok the of observations M 1 cm ff c fetra etn asstecodds–eprtr t dust–temperature cloud the causes heating external of ect − ⊙ 2 h oa yrgnms fC 4 asmn itneo 200 of distance a (assuming 244 CB of mass total The . n h aso h trescr s5 is core starless the of mass the and 1 .Krause O. , ihimpor- with d L 1 te othe to etter .Henning T. , etailed spro- ts 17Hiebr,Germany Heidelberg, 9117 . epetla nntr,sprtdb 90 by separated nature, in prestellar be ABSTRACT ally, .Andr´eP. µ oac h CB 850 SCUBA the mosaic, m r hrfr da o uttmeaueadclm densit column and dust–temperature for ideal therefore are n, ic l. d s - - yo rzn,93NrhCer vne usn Z871 USA 85721, AZ Tucson, Avenue, Cherry North 933 Arizona, of ty ttmeauena h rtsa is protostar the near st–temperature eettefis esrdds–eprtr a fa nies entire an of map dust–temperature measured first the resent + lbl yLuhrt(96 n hre ta.(00 n pro and (2000) t 8 al. inside an star- et source Shirley both 244 CB additional and duces (1996) an the Launhardt as of by published globule detection first the was core while less 1991), al. et Clemens tdwt trescr oae tR.A. at located core starless a with ated um ek,oeascae ihaCas0pootrlocated protostar 0 Class a with R.A. at associated one peaks, submm h S n trescr r eaae by separated are core starless and YSO The etof tent h oreC 4 a bevdwt h ASisrmn on instrument PACS the with the observed board was 244 CB source The observations Herschel 2.1. distance a source at The globule contribution. Bok this a of is focus 1962) of Lynds the (L1262; is 244 CB sample the of .Osrain n aaprocessing data and Observations 2. globules. bala isolated energy the in in cores envelopes such the of ex by of shielding role and the heating reveal nal also distribut They mass accuracy. and unprecedented profiles with density the reconstruc hence to and o us globule distribution allow Bok density data column These b and SED. map cover dust–temperature the that the of cloud peak the entire of the sides of (SEDs) distributions energy bands SPIRE and PACS use We the throughout resolved well therefore 74 1 4 E ∼ / evc ’srpyiu,CE aly redsMerisiers, des Orme Saclay, C.E. d’Astrophysique, Service .Kainulainen J. , ◦ ditor 18 0 c(itn&Lhla19) iha prxmt ex- approximate an with 1995), Lahulla & (Hilton pc 200 evtie 51 ai,France Paris, 75014 servatoire, ∼ ± ′ s,extinction ust, Herschel = 25 M 2 6 Herschel 23 . ′ 3 raot05p.TeC 4 lbl otistwo contains globule 244 CB The pc. 0.5 about or , bl B4.I otistocl ore,alow– a sources, cold two contains It CB244. obule ′′ h ⊙ 25 h rtsa rvsamlclroto (e.g., outflow molecular a drives protostar The . niaigthat indicating , m mgn ocntutsailyrsle spectral resolved spatially construct to imaging µ 46 Tbne l 00 n 24 a and 2010) al. et (Tobin m pc bevtr n20,Dcme 30, December 2009, on Observatory Space µ . 1 3 a,adteIA . mmp we map, mm 1.3 IRAM the and map, m .Nielbock M. , s Decl. , ieto rise o ′′ ( ∼ ∼ ∼ 5 ftems nteglobule the in mass the of 45% + = 80 U.The AU). 18000 17 ∼ c s15 is pc) . 74 ,wiefrtestarless the for while K, 7 7Kweetehydrogen the where K 17 ◦ 1 17 .Steinacker J. = ′ 39 ± 23 . M 5 1 ⋆ h ′′ Herschel 25 n n associ- one and , ⊙ modeling. y ∼ m h mass The .

27 c 90 µ . S 2018 ESO 3 1 shadow. m ′′ , s 1 n are and , data tar– Decl. , and , the f nce ter- oth he = - t . 2 A. Stutz et al.: Dust–temperature Structure of CB 244

Fig. 1. 8′ × 8′ images of CB244, shown at the wavelengths indicated in the bottom–right of each panel. The images are shown on a log scale at stretches intended to highlight the structure of absorption or emission at each wavelength. The locations of the protostar and starless core, derived from the 8 µm image, are indicated with ×–symbols (note the offset between the ×’s and the starless core emission at 100 – 250 µm wavelengths). The panel contours ‘are labeled with their corresponding wavelengths. The contour levels are: AV extinction map levels = {5,10,15,20,25} mags (inner dotted contours indicates the region inside which we place lower–limits on the extinction); SPIRE 350 µm = {0.5,1.0,1.5,3.5} mJy/⊓⊔′′; SCUBA 850 µm = {0.3,0.75} mJy/⊓⊔′′; IRAM 1.3 mm = {0.1,0.3} mJy/⊓⊔′′. Approximate beam sizes are indicated as yellow circles.

during the Science Demonstration Program. The globule CB 244 as well as a correction for offsets in the detector sub–matrices was observed at 100 µm and 160 µm. We obtained two orthog- were performed. Finally, the data were highpass–filtered, using onal scan maps with scan leg lengths of 9′ using a scan speed a median window with a width of 271 data samples to remove of 20′′/s. The scan leg position angles guarantee an almost ho- the effects of bolometer temperature drifts during the course of mogeneous coverage of CB244. We produced highpass–filtered the data acquisition. Furthermore, we masked emission struc- intensity maps from these data using the HIPE software package tures, in this case both the YSO and starless core regions, before (Ott 2010), version 3.0, build 455. Besides the standard steps computing the running median. Masking bright sources mini- leading to level–1 calibrated data, a second–level deglitching mizes over–subtraction of source emission in the highpass fil- A. Stutz et al.: Dust–temperature Structure of CB 244 3 tering step. Finally, the data were projected onto a coordinate 3. Dust temperature and column density modeling grid using the photProject routine inside HIPE. As a last step, the flux correction factors provided by the PACS ICC team were We used the PACS 100 and 160 µm, SPIRE 250, 350, and applied. We note that these data have relatively flat background 500 µm data in conjunction with the NIR extinction map, MIPS values, indicating that the highpass reduction used in conjunc- 70 µm, SCUBA 850 µm, and IRAM 1.3 mm dust emission maps tion with the masking is a relatively robust scheme for avoiding to model the line–of–sight–averaged temperature and column artifacts and recovering extended emission in the PACS maps. density of CB244. The calibrated maps were all homogeneously In addition to these processing steps, we checked the pointing in convolved to the largest FWHM beam size–of the data set, the SPIRE 500 µm 37′′ beam, assuming Gaussian beam profiles, the PACS 100 µm map against the MIPS 24 µm mosaic of the ′′ −1 same region. Using point–sources detected in both images, we and projected onto a common 8 pix grid. This approach has found a pointing offset of ∼ 1.25′′ in the 100 µm map relative to the drawback that all spatial structures smaller than this beam the 24 µm mosaic. Because the 160 µm PACS map contains no size are smoothed, but ensures that the fluxes at all wavelengths point–sources and was acquired at the same time as the 100 µm in a given image pixel are derived from the same area in the data, we blindly applied the same pointing correction. The final source. We corrected the filtering of large spatial–scale emission PACS 100 and 160 µm images are shown in Fig. 1. in the PACS data using the Schlegel et al. (1998) 100 µm IRAS maps and the ISO Serendipity Survey observations at 170 µm: Maps at 250, 350, and 500 µm were obtained with SPIRE we added a zero level of emission of 0.3 and 0.8 mJy/⊓⊔′′ to the ′ on October 20, 2009. Two 9 scan legs were used to cover the 100 and 160 µm maps, respectively. source. Two repetitions resulted in 146 s of scanning time with For each image pixel, an SED was extracted and fitted ′′ the nominal speed of 30 /s. The data were processed within with a single–temperature modified black–body of the form HIPE with the standard photometer script up to level 1. During S =Ω B (ν, T ) 1 − e−τ(ν) , where Ω is the solid angle of the baseline removal, we masked out the high–emission area in the ν ν d   center of the field. For these data no cross-scan was obtained; emitting element, Bν is the Planck function, Td is the dust– therefore, the resulting maps still showed residual stripes along temperature, and τ(ν) is the optical depth at frequency ν. In a the scan direction. We used the Bendo et al. (2010) de–stripping first iteration, we used a simple dust opacity model of the form κ ∝ νβ β χ2 β = . scheme to mitigate this effect. In addition, we checked the point- ν to fit for , using minimization. We found that 1 9 ing in the SPIRE data by cross–correlating the images with the – 2 fited the data best over the entire cloud. Note that compact PACS 160 µm image; we found that the pointing offsets for all structures were smoothed out; therefore this cannot be taken as three wavelengths are on order of 2′′ or smaller, and therefore evidence against grain growth in the centers of the two dense we did not correct for this. The SPIRE 250, 350, and 500 µm cores. In a second step, we then fixed the dust model to the images are shown in Fig. 1. Ossenkopf & Henning (1994) model for an MRN grain size dis- tribution, with thin ice mantles and no coagulation, which has 2 −1 a κ1.3mm = 0.51cm g . The hydrogen–to–dust mass ratio was 2.2. Other data fixed to the canonical value of 110 (e.g., ?). We then searched for the optimum Td and hydrogen column density NH values (the two free parameters) by calculating flux densities and A Near-IR data: We observed CB244 in the near-IR KS and H V bands using Omega2000at the Calar Alto Observatory.The 15′× values and then comparing to the emission and extinction ob- 2 15′ field–of–view provided complete coverage of the globule. A servations, using χ minimization. The resulting line–of–sight– standard near–IR data reduction scheme was adopted. The ex- averaged dust–temperature and column density maps are shown tracted photometric data where calibrated using the Two Micron in Fig. 2, together with the SED fits at the central positions of All Sky Survey (2MASS; Skrutskie et al. 2006). Following the the two submillimeter peaks. We found the best–fit column– averaged dust–temperatures for the protostar and prestellar core NICE method (Lada et al. 1994), the observed (H − KS ) colors of ∼17.7Kand ∼10.6 K, respectively. Despite the fact that each of stars were then related to visual extinction by (H − KS ) = individual image pixel was fitted independently and the maps at h(H−KS )0i+0.063×AV, assuming the Rieke & Lebofsky(1985) different wavelengths have different outer boundaries, both the extinction law, where h(H − KS )0i is the mean intrinsic color of temperature and the column density maps have very little noise the stars determined from edges of the field. The AV values for each star were used to create an extinction map. The resulting and are very smooth, demonstrating the robustness of our fit- ting approach. Furthermore, we evaluated the effect of a possi- extinction map probes extinction values up to AV ≈ 30 mag, ble filtered–out extended emission component in the chopped with a 3σ error of about 3 mag at AV = 0 mag. 850 µm and 1.3 mm maps. Adding in offsets of 60mJy/15′′ Spitzer data: The Spitzer observations presented here are from ′′ two programs: the MIPS observations are from program 53 (P.I. beam at 850 µm and 12mJy/11 beam at 1.3mm, correspond- G. Rieke), while the IRAC observations are from program 58 ing to 20% of the peak surface brightness of the cold prestellar (P.I. C. Lawrence). The MIPS observations were reduced using core, did not affect the fitted temperature and column density the Data Analysis Tool (DAT; Gordon et al. 2005) according to (less than a 2% change) for the prestellar core or the protostar. steps outlined in Stutz et al. (2007). The IRAC frames were pro- Hence, we conclude that possible missing extended emission in cessed using the IRAC Pipeline v14.0, and mosaics were created the (sub)mm maps does not affect our results. from the basic calibrated data (BCD) frames using a custom IDL program (see Gutermuth et al. 2008). 4. Summary and conclusions (Sub)mm continuum data: The SCUBA 850 µm and the IRAM 1.3 mm maps are presented in Launhardtetal. (2010). The As shown in Fig. 2, the line–of–sight–averaged dust– 850 µm and 1.3 mm maps cover both sources, but do not ex- temperature decreases constantly without any significant jump tend very far into the envelope. The maps have native beam from ∼ 17 ± 1 K at the outer boundary of the cloud, where ′′ ′′ 21 −2 sizes of 14.9 (850 µm), and 10.9 (1.3 mm). For further de- NH drops below 10 cm and AV ≈ 0.3mag, to ∼ 13K in 22 −2 tails see Launhardt et al. (2010). In Fig. 1 we show the 850 µm the inner cloud at NH ≈ 1—2 × 10 cm and AV ≈ 3 – and 1.3 mm emission as contours. 5mag. Note that due to the two major drawbacks of our sim- 4 A. Stutz et al.: Dust–temperature Structure of CB 244

Fig. 2. Dust–temperature (color) and hydrogen column density (white contours) in CB244. The line–of–sight–averaged mean dust– temperature was derived pixel by pixel from modified black–body SED fits to homogeneously beam–smoothed emission maps from Herschel PACS and SPIRE, Spitzer MIPS70, and ground–based extinction mapping and submillimeter dust–continuum maps at 0.8 and 1.3mm (see text for details). The top color bar indicates the temperature scale. Column density contours are at {0.1 (thick) 0.3, 0.5, 1 (thick), 2, 3.5, 5, and 7}×1022 H/cm2. The peak column density in the prestellar core just reaches 1023 H/cm2. Two SEDs and the respective modified black–body fits are shown for the positions of the Class0 protostar (“1”) and the prestellar core (“2”). The yellow dashed ellipses indicate the areas used to calculate source (see Sect. 4). The 37′′ beam size is indicated by a grey circle. White areas represent regions where there is not enough signal–to–noise and/or coverage to get a reliable fit.

plified approach, beam–smoothing and line–of–sight–averaging, Including the new Herschel data, we derive the following pa- the local dust–temperatures at the source centers will be higher rameters for the protostar: Lbol ∼1.5L⊙,Lsubmm/Lbol ∼ 4%, Tbol ∼ in the protostar and lower in the prestellar core. Nevertheless, 62 K, and Menv/Lbol ∼ 1.45 M⊙/L⊙, (cf. Launhardt et al. 2010), the boundaries of the two sources can be derived from the dust– confirming the Class 0 classification according to Chen et al. temperature map rather than from the smooth column density (1995) and Andre et al. (2000). Furthermore, the C18O (2–1) −1 map. We find that Td = 13K marks the mean inner dust– FWHM line width for the prestellar core is ∼0.9kms (Stutz et temperature of the globule, from where the temperature towards al., in prep.); using our fitted prestellar core mass and tempera- the protostar rises steeply and that of the prestellar core de- ture, we find that the ratio of gravitational energy to thermal and creases. We therefore adopt ellipses that follow the 13K con- turbulent energy is Egrav / (Etherm + Eturb) ≃ 0.9, a marginally tour in the dust–temperature map as boundaries for the two sub–critical value which is expected for prestellar cores. For ′′ sources (see Fig. 2). The mean radii of these ellipses are 50 comparison, Tobin et al. (2010) derive a mass of ∼3–4M⊙ for (10,000 AU) for the protostellar core and 76′′ (15,000 AU) for the prestellar core (integrated over a similar area and scaled to a the prestellar core. Integration of the column density map within distance of 200 pc) using the 8 µm shadow (see Fig. 1), a good these boundaries yields MH = 1.6 ± 0.3M⊙ for the protostel- agreement given the uncertainties in both mass derivation meth- lar core and MH = 5 ± 2M⊙ for the prestellar core, where the ods. The prominent and extended 3.6 µm coreshine (see Fig. 1), uncertainties are derived from an assumed ±1K uncertainty in originating from dust–grain scattering of the background radi- the dust–temperature. The total mass of the globule (within the ation field, is an indication of grain growth (Steinacker et al. 21 −2 NH = 1 × 10 cm contour) is MH = 15 ± 5M⊙. We note that 2010) in the CB244 cloud. These pieces of evidence together Mgas = 1.36MH. These masses imply that ∼45% of the mass of indicate that the CB 244 globule, and other globules like it, are the globule is participating in the star–formation process. excellent sources in which to study the earliest phases of low– mass star–formation.As a next step and in a follow–uppaper, we A. Stutz et al.: Dust–temperature Structure of CB 244 5 will employ 3D–modeling to overcome the effects of line–of– sight averaging and beam-smoothing, and to reconstruct the full dust–temperature and density structure of CB244 and the other sources in our sample. Measuring reliable temperatures and col- umn densities with the Herschel data in a sample of prestellar and protostellar cores is a fundamental step towards revealing the initial conditions of low–mass star–formation.

Acknowledgements. The authors thank J. Tobin for helpful discussions and D. Johnstone for a critical and helpful referee report. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF- IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). SPIRE has been developed by a consor- tium of institutes led by Cardiff University (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); Stockholm Observatory (Sweden); STFC (UK); and NASA (USA).

References Andre, P., Ward-Thompson, D., & Barsony, M. 2000, and IV, 59 Bendo, G. J. et al. 2010, A&A, this volume Chen, H., Myers, P. C., Ladd, E. F., & Wood, D. O. S. 1995, ApJ, 445, 377 Clemens, D. P. & Barvainis, R. 1988, ApJS, 68, 257 Clemens, D. P., Yun, J. L., & Heyer, M. H. 1991, ApJS, 75, 877 Gordon, K. D. et al. 2005, PASP, 117, 503 Griffin, M. J. et al. 2010, A&A, this volume Gutermuth, R. A., Myers, P. C., Megeath, S. T., et al. 2008, ApJ, 674, 336 Hilton, J. & Lahulla, J. F. 1995, A&AS, 113, 325 Lada, C. J., Lada, E. A., Clemens, D. P., & Bally, J. 1994, ApJ, 429, 694 Launhardt, R. 1996, PhD thesis, PhD Thesis, University of Jena, (1996) Launhardt, R. & Henning, T. 1997, A&A, 326, 329 Launhardt, R. L. et al. 2010, submitted to ApJ Lynds, B. T. 1962, ApJS, 7, 1 Ossenkopf, V. & Henning, T. 1994, A&A, 291, 943 Ott, S. 2010, in ASP Conference Series, Vol. 00, Astronomical Data Analysis Software and Systems XIX, 00 Pilbratt, G. L. et al. 2010, A&A, this volume Poglitsch, A. et al. 2010, A&A, this volume Rieke, G. H. & Lebofsky, M. J. 1985, ApJ, 288, 618 Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525 Shetty, R., Kauffmann, J., Schnee, S., Goodman, A. A., & Ercolano, B. 2009, ApJ, 696, 2234 Shirley, Y. L., Evans, II, N. J., Rawlings, J. M. C., & Gregersen, E. M. 2000, ApJS, 131, 249 Skrutskie, M. F., Cutri, R. M., Stiening, R., et al. 2006, AJ, 131, 1163 Steinacker, J., Pagani, L., Bacmann, A., & Guieu, S. 2010, A&A, 511, A9+ Stutz, A. M., Rieke, G. H., Bieging, J. H., et al. 2009, ApJ, 707, 137 Stutz, A. M. et al. 2007, ApJ, 665, 466 Stutz, A. M. et al. 2008, ApJ, 687, 389 Tobin, J. J., Hartmann, L., Looney, L. W., & Chiang, H. 2010, ApJ, 712, 1010 Ward-Thompson, D., Andr´e, P., Crutcher, R., et al. 2007, Protostars and Planets V, 33