103 Acta Polytechnica CTU Proceedings 1(1): 103–107, 2014 103 doi: 10.14311/APP.2014.01.0103 The Formation of Massive Stars: from Herschel to Near-Infrared Paolo Persi1, Mauricio Tapia2 1Institute for Space Astrophysics and Planetology (IAPS/INAF) Via fosso del cavaliere 100, 00133 Roma, Italy 2Instituto de Astronomia,UNAM, Apartado Postal 877,Ensenada, Baja California, CP22830, Mexico Corresponding author: paolo.persi@iaps.inaf.it Abstract We have studied a number of selected high mass star forming regions, including high resolution near-infrared broad- and narrow-band imaging, Herschel (70, 160, 250, 350 and 500 µm) and Spitzer (3.6, 4.5, 5.8 and 8.0 µm) images. The preliminary results of one of this region, IRAS 19388+2357(MOL110) are discussed. In this region a dense core has been detected in the far-infrared, and a young stellar cluster has been found around this core. Combining near-IR data with Spitzer and Herschel photometry we have derived the spectral energy distribution of Mol110. Finally comparing our H2 and Kc narrow-band images, we have found an H2 jet in this region. Keywords: star formation - circumstellar matter - giant molecular clouds - infrared. 1 Introduction The formation of high-mass stars defined as those with masses greater than 8 Msun is still controversial. One of the crucial problem is to understand if high-mass stars can form through(disk) accretion like low-mass stars. Such stars reach the zero-age main sequence (ZAMS) still undergoing heavy accretion, and their powerful ra- diation pressure should halt the infalling material, thus inhibiting growth of the stellar mass beyond about 8 Msun (e. g., Palla & Stahler 1993). Recently, various studies have proposed a solution to this problem based on non-spherical accretion and high accretion rates (e. g., McKee & Tan 2003; Bonnell et al. 2004; Kuiper et al. 2010). In addition at difference of low-mass stars, high-mass stars forms in cluster. Therefore the compre- hension of the massive star formation process requires good observational knowledge of the star-forming envi- ronment and of the evolutionary steps through which OB star formation occurs. This can be made combin- ing observations at different wavelengths from near to far-infrared and millimeter wavelengths. Thanks to the Spitzer and Herschel satellites that operate from the mid-IR to the sub-millimeter it is now possible to have a broad observational coverage of these high mass star formation regions. We have selected a number of these regions reported in Table 1 with typical characteristics of high-mass star formation(i.e. presence of water and methanol maser sources, radio and millimeter emission , ammonia cores, (Molinari et al.1998, Molinari et al. 2000). The type High(H) and Low(L) reported in Table 1 are taken from Molinari et al.1996.. We obtained sub- arcsec resolution near- infrared broad- and narrow-band images of the source of Table 1. These observations are compared with far-IR images from the Herschel In- frared GALactic plane survey (Hi-GAL, Molinari et al. 2010) supplemented with Spitzer/IRAC archive images. The observations are described in Section 2, while in Section 3 we report the preliminary results of IRAS 19388+2357(Mol110). All the results will be discussed in forthcoming papers. Table 1: Sample of the observed high-mass protostars Source Type IRAS α(2000) δ(2000) D L h m s ◦ ′ ” Kpc L� Mol83 H 18566+0408 18 59 10.0 04 12 15 6.8 1.02 × 105 Mol98 L 19092+0841 19 11 37.4 08 46 30 4.5 9.20 × 105 G45.07+0.13 19110+1045 19 13 22.6 10 50 53 9.7 1.42 × 105 G45.47+0.13 19 14 08.3 11 12 32 6.0 3.80 × 105 Mol110 H 19388+2357 19 40 59.4 24 04 39 4.3 1.48 × 104 103 http://dx.doi.org/10.14311/APP.2014.01.0103 Paolo Persi, Mauricio Tapia 1.1 Near-infrared images Near-infrared images through narrow-band H2 (λo = 2.122 µm, ∆λ = 0.032 µm ) and Kcont ( λo = 2.270 µm, ∆λ = 0.034 µm) filters, as well as through standard broad-band JHKs filters, were collected on the nights of 2008 July 12 and 14 using the Near Infrared Camera Spectrometer (NICS) attached to the 3.58m Telesco- pio Nazionale Galileo (TNG) at the Observatorio del Roque de los Muchachos on La Palma island. NICS has a HgCdTe Hawaii 1024 ×1024 array and was used in the SF (small field) configuration with a plate scale of 0.13 arcsec/pixel. In each band, 9 dithered frames spaced by 10 arcsec were taken and coadded, for to- tal on-source integration times of 630 s, 540 s and 360 s for J, H, and Ks, respectively. The total integra- tion time for each of the narrow-band (H2 and Kcont) filters was 1170 s. All images were calibrated using photometric standard stars from Hunt et al. (1998) and Persson et al. (1998). The measured FWHM of the point-spread function (PSF) is between 0.6 arcsec and 0.8 arcsec. JHK photometry was obtained using DAOPHOT (Stetson 1987) within IRAF in the stan- dard way, with an aperure of 1 arcsec. For the crowded regions, we used the PSF procedure, also within IRAF. 1.2 HI-GAL images Hi-Gal is a Herschel open time key-project (Molinari et al.2010) aiming at mapping the Galactic plane with the PACS (70 and 160 µm, Poglitsch et al. 2010) and SPIRE (250, 350, and 500 µm, Griffin et al. 2010) photometers on board the Herschel satellite (Pilbratt et al. 2010). Our target were observed by SPIRE+PACS in parallel mode at a scan speed of 60 arcsec/s. The data were reduced using the Hi-GAL standard pipeline (Traficante et al. 2011). The images have pixel sizes 3.2 arcsec, 4.5 arcsec, 6 arcsec, 8 arcsec, and 11.5 arcsec , at 70, 160, 250, 350, 500 µm respectively. From the im- ages, we performed the source extraction and photom- etry using the Curvature Threshold Extractor package (CuTEx, Molinari et al. 2011). 1.3 Spitzer/IRAC archive images Flux-calibrated images of our regions were retrieved from the GLIMPSE (Benjamin et al. 2003, Churchwell et al. 2009) survey taken at 3.6, 4.5, 5.8 and 8 µm with IRAC on board the Spitzer Space Observatory . The flux densities of the mid-infrared counterparts of our sources were extracted from the GLIMPSE Catalogue. 2 IRAS19388+2357(Mol110) IRAS 19388+2357 is associated with H2O maser emis- sion (Palla et al. 1991; Brand et al. 1994), a ra- dio source (Hughes & MacLeod 1994; Molinari et al. 1998) and dense molecular gas traced in NH3 by Moli- nari et al. (1996) who renamed as Mol110. Methanol maser was also detected from this source (Schutte et al. 1993; Slysh et al. 1994). Zhang et al. (2005) de- tected a CO outflow. The centroid of their CO emission is approximately 29 arcsec south of the IRAS position. Finally Beltran et al.(2006) detected a dense core at 1.2mm with a mass of 167 Msun. The presence of a UCHII region, of water and methanol maser, confirm that Mol110 is an high-mass star forming region. Fig- ure 1 shows our Ks-band image including the positions of the mentioned sources. Figure 1: Ks-band image of IRAS19388+23657. The plus indicates the position of the IRAS source, while the open circle and the cross give the positions of the 6cm radio continuum and the MSX source respectively. The contours represent the 1.2mm emission. A point-like far-infrared sources has been detected in the HI-GAL Herschel images from 70 to 500 µm at the position α2000 = 19 h40m59.2s, δ2000 = +24 ◦ 04’ 44.9”. We have analyzed our JHKs and Spitzer images within an area of approximately 20” × 20” around this position. Figure 2 reports the color-coded JHKs and Spitzer images of this area. Within the Herschel beam we found several very red sources. We have obtained the JHKs photometry of these sources around the Her- schel peak position. From this photometry, we have obtained the J − H versus H − Ks diagram illustrated in Figure 3. More than 14 objects show significant near-infrared excess, suggesting the presence of a young stellar cluster in this region. The positions of these sources are marked in Fig.2 (left panel). At least six of these sources are iden- tified with the mid-IR Spitzer sources (see Fig.2 right panel). 104 The Formation of Massive Stars: from Herschel to Near-Infrared Figure 2: (Left panel) JHKs color-coded image of IRAS19388+2375 obtained combining the J (blue), H (green), and Ks (red) individual images The contours show the 70 µm Herschel observation. The symbol (+) marks the positions of the sources with near-IR excess, while the crosses indicate sources not detec- tect in J but with H-Ks greater than 3(Right panel) Color-coded Spitzer image obtained combining the [3.6] (blue), [4.5] (green), and [8.0] µm (red) individual IRAC images. The central position of the two images is α2000 = 19 h40m59.1s, δ2000 = +24 ◦ 04’ 45.4”. North is at the top and east to the left. Figure 3: J-H versus H-Ks diagram relative to a region of 20arcsec around the IRAS position. On the base of the position coincidence, we have identified the far-IR source with a near-IR and Spitzer source. At the same position a source has been de- tected also with the WISE satellite. Combining data from near-IR to millimeter spectral region we have constructed the spectral energy distribution (SED) of Mol110 reported in Figure 4. The SED has been fitted with the infalling enve- lope+disc+central source radiation transfer model de- scribed by Robitaille et al. (2006) by using the fitting tool of Robitaille et al. (2007). The parameters of the model that best fit the SED are reported in Table 2. Figure 4: Spectral energy distribution (SED) of Mol 110 The observed luminosity of 1.13 104 L� correspond to that of a B1-2 ZAMS star reddened by 50.2 magni- tudes of extinction in V. 105 Paolo Persi, Mauricio Tapia Figure 5: (Left panel) H2 narrow-band image of IRAS 19388+2357. (Right panel) Narrow-band Kc image of the same region. North is at the top and east to the left. Table 2: Physical parameters of Mol 110 derived from the Robitaille et al. (2007) model. Stella Mass (Msun) 12.94 Stellar Temperature (K) 12262 Envelope Accretion Rate (Msun/yr) 3.61 10 −3 Envelope Outer Radius (AU) 1.0 105 Envelope Cavity Angle (deg) 25.1 Disk Mass (Msun) 1.4910 −1 Disk Outer Radius (AU) 23.1 Disk Accretion Rate (Msun/yr) 5.18 10 −6 AV 50.2 D(kpc) 4.7 Lbol 1.13 10 4 L� From the comparison of our narrow-band images centered on the H2 (λo = 2.122 µm), and nearby con- tinuum Kcont ( λo = 2.270 µm), we have found an H2 jet at the position α2000 = 19 h40m59.7s, δ2000 = +24 ◦ 04’ 49.0” . A nearby source at the position α2000 = 19h40m59.5s, δ2000 = +24 ◦ 04’ 47.6” with near-IR ex- cess could be the young stellar object (YSO) driving the observed outflow. This is illustrated in Figure 5. Sim- ilar observations obtained by Varricatt et al. (2010) report three different H2 jets in the region not detected in our images. The positions of these H2 jets are very far from the CO outflow observed by Zhang et al. (2005), indicating that another YSO is responsible of driving this outflow. 3 Conclusions In order to understand the physical processes that in- volve high massive star forming regions, the comparison of observations at different wavelengths from near-IR to millimeter are fundamental. We have here reported an example of this combined analysis including near-IR images, Spitzer data from 3.6 to 8 µm and Herschel images in five bands from 70 to 500 µm, relative to the star forming region IRAS 19388+2357. From this anal- ysis the following conclusions can be made: 1) A very dense and cold core has been detected from the far- IR Herschel images, in proximity of the IRAS source. 2) Within the dense core the near-IR images show the presence of a young stellar cluster of at least 15 mem- bers in a radius of 20 arcsec. 3) The far-IR peak has been identified with a bright Spitzer and near-IR source. Combining the photometry from 1.25 µm to 1.2mm, we have derived its spectral energy distribution(SED). The measured total luminosity indicates that the source is a 106 The Formation of Massive Stars: from Herschel to Near-Infrared B1-2 ZAMS with AV =50.2 4) Finally, the narrow-band image centered on the H2 line at 2.122 µm shows the presence of an H2 jet in proximity of the IRAS source. References [1] Beltran, M. T., Brand, J., Cesaroni, R., et al.: 2006, A&A, 447, 221 [2] Benjamin, R. A., Churchwell, E., Babler, B. L., et al.: 2003, PASP, 115, 953 doi:10.1086/376696 [3] Bonnell, I. A., Vine, S. G., Bate, M. R.: 2004, MNRAS, 349, 735 doi:10.1111/j.1365-2966.2004.07543.x [4] Brand J., et al.: 1994, A&AS, 103, 541 [5] Churchwell, E., Babler, B. L., Meade, M. R., et al.: 2009, PASP, 121, 213 doi:10.1086/597811 [6] Griffin, M. J., Abergel, A., Abreu, A., et al.: 2010, A&A, 518, L3 [7] Hughes V. A., MacLeod G. C.: 1994, ApJ, 427, 857 [8] Hunt, L. K., Mannucci, F., Testi, L., et al.: 1998, AJ, 115, 2594 [9] Kuiper, R., Klahr, H., Beuther, H., Henning, T.: 2010, ApJ, 722, 1556 doi:10.1088/0004-637X/722/2/1556 [10] McKee, C. F., Tan, J. C.: 2003, ApJ, 585, 850 doi:10.1086/346149 [11] Molinari S., Brand J., Cesaroni R., Palla F.: 1996, A&A, 308, 573 [12] Molinari, S., Brand, J., Cesaroni, R., Palla, F., Palumbo, G. G. C.: 1998, A&A,336, 339 [13] Molinari, S., Brand, J., Cesaroni, R., Palla, F.: 2000, A&A, 355, 617 [14] Molinari, S., Swuyard, B., Bally, J., et al.: 2010, A&A, 518, L100 [15] Molinari, S., Faustini, F., Schisano, E., et al.: 2011, A&A, 530, A133 [16] Palla F., Brand J., Cesaroni R., Comoretto G., Felli M.: 1991,A&A, 246, 249 [17] Palla, F., Stahler, S. W.: 1993, ApJ, 418, 414 [18] Persson, S. E., Murphy, D. C., Krzeminski, W., et al.: 1998, AJ, 116, 2475 [19] Pilbratt, G. L., Riedinger, J. R., Passvogel, T., et al.: 2010, A&A, 518, L1 [20] Poglitsch, A., Waelkens, C., Geis, N., et al.: 2010, A&A, 518, L2 [21] Robitaille, T. P., Whitney, B. A., Indebe- touw, R., et al.: 2006, ApjS, 167, 256 [22] Robitaille, T. P., Whitney, B. A., Indebetouw, R., Wood, K.: 2007, ApjS, 169, 328 [23] Schutte A. J., van der Walt D. J., Gaylard M. J., MacLeord G. C.: 1993, MNRAS, 261, 783 [24] Slysh V. I., Dzura A. M., Valtts I. E., Gerard E.: 1994, A&AS,106, 87 [25] Stetson, P. B.: 1987, PASP, 99, 191 [26] Traficante, A., Calzoletti, L., Veneziani, M., et al.: 2011, MNRAS, 416, 2932 [27] Varricatt, W. P., Davis, C. J., Ramsay, S., Todd, S. P.: 2010, MNRAS, 404, 661 bibitem Zhang Q., Hunter T. R., Brand J., et al.: 2005, ApJ, 625, 864 107 http://dx.doi.org/10.1086/376696 http://dx.doi.org/10.1111/j.1365-2966.2004.07543.x http://dx.doi.org/10.1086/597811 http://dx.doi.org/10.1088/0004-637X/722/2/1556 http://dx.doi.org/10.1086/346149 Introduction Near-infrared images HI-GAL images Spitzer/IRAC archive images IRAS19388+2357(Mol110) Conclusions