Different evolutionary stages in the massive star-forming region S255 complex

Abstract

Aims. Massive stars form in clusters, and they are often found in different evolutionary stages located close to each other. To understand evolutionary and environmental effects during the formation of high-mass stars, we observed three regions of massive star formation at different evolutionary stages, and all are found that in the same natal molecular cloud. Methods. The three regions, S255IR, S255N, and S255S, were observed at 1.3 mm with the submillimeter array (SMA), and followup short spacing information was obtained with the IRAM 30 m telescope. Near infrared (NIR) H + K-band spectra and continuum observations were taken for S255IR with VLT-SINFONI to study the different stellar populations in this region.Results. This combination of millimeter (mm) and near infrared data allow us to characterize different stellar populations within the young forming cluster in detail. While we find multiple mm continuum sources toward all regions, their outflow, disk, and chemical properties vary considerably. The most evolved source S255IR exhibits a collimated bipolar outflow visible in CO and H 2 emission, and the outflows from the youngest region S255S are still small and fairly confined in the regions of the mm continuum peaks. Also the chemistry toward S255IR is the most evolved, exhibiting strong emission from complex molecules, while much fewer molecular lines are detected in S255N, and in S255S we detect only CO isotopologues and SO lines. Also, rotational structures are found toward S255N and S255IR. Furthermore, a comparison of the NIR SINFONI and mm data from S255IR clearly reveal two different (proto) stellar populations with an estimated age difference of approximately 1 Myr. Conclusions. A multiwavelength spectroscopy and mapping study reveals different evolutionary phases of the star formation regions. We propose the triggered outside-in collapse star formation scenario for the bigger picture and the fragmentation scenario for S255IR.

Disk-mediated accretion burst in a high-mass young stellar object

“…Similarly, flux densities for the N60 and N160 AKARI bands were derived from the corresponding images after retrieval from the ISAS/JAXA archive (the wide AKARI channels centred at 90 and 140 µm are saturated). These data were complemented with an archival ISO/SWS spectrum (courtesy D. Whittet), H and Ks VLT/ISAAC photometry (private communication by S. Correia, ESO proposal ID 074.C-0772(B)) as well as flux densities from the literature 13,14,[37][38][39] and surveys (AKARI, BGPS, MSX, UKIDSS). The outburst SED was obtained using data from PANIC, GROND, SINFONI, FORCAST and FIFI-LS taken in February 2016.…”

“…SINFONI pre-outburst IFU spectra, taken between February and March 2007, were retrieved from the ESO Data Archive and have already been published in a previous paper 14 . They map an area (70 × 70 ) larger than our observations.…”

“…Moreover, the released energy and the inferred mass-accretion rate are also orders of magnitude larger. Our results identify disk-accretion as the common mechanism of star formation across the entire stellar mass spectrum.S255IR NIRS 3 (aka S255IR-SMA1) is a well-studied ∼20 M (L bol ∼ 2.4×10 4 L ) high-mass young stellar object (HMYSO) 13,14 in the S255IR massive star-forming region 13 , located at a distance of ∼1.8 kpc 15 . It exhibits a disk-like rotating structure 13 , very likely an accretion disk, viewed nearly edge-on 16 (inclination angle ∼80 • ).…”

“…The right-hand panel of Fig. 2 compares our NIFS/Gemini spectrum (in black) of the redshifted outflow lobe with the SINFONI/VLT pre-outburst spectrum 14 of the same region (red spectrum). The new spectrum shows an increase in luminosity for both the continuum and lines (H 2 , Brγ ), as well as the appearance of new emission lines, namely CO band-heads, Na I, He I, which are typically observed in young eruptive low-mass stars (EXors, FUors and MNors 1,[19][20][21][22][23] ) and are the typical signature of accretion disks, accretion and ejection activity.…”

“…This would also explain the LETTERS observation of several knots in jets from HMYSOs 28 , assuming major outflows events can be linked to major accretion events. Indeed, the morphology of different gas tracers along the outflow axis of NIRS 3, which shows a discrete number of knots, suggests that the source experienced multiple bursts within the past few thousand years [13][14][15] . Our burst detection proves the erratic behaviour of the accretion process in HMYSOs.…”