- ID:
- ivo://CDS.VizieR/J/A+A/625/A134
- Title:
- NGC 6357 massive dense cores
- Short Name:
- J/A+A/625/A134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) able to form high-mass star(s). It is one of purposes of the Herschel/HOBYS key program. Here, we make the census and characterisation of the properties of the MDCs population of the NGC 6357 HII region. Our study is based on the Herschel PACS and SPIRE 70-500 microns images of NGC 6357 complemented with (sub)millimetre and mid-infrared data. We followed the procedure, established by the Herschel/HOBYS consortium, to extract ~0.1pc massive dense cores using the getsources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting. We have obtained a complete census of 23 massive dense cores, amongs which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we consider their evolutionary status, and suggest that only five are likely to form a high-mass star. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge/hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/647/A154
- Title:
- NGC6357 686 molecular cores physical properties
- Short Name:
- J/A+A/647/A154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We mapped the NGC6357 star forming region at 450 and 850 micron with SCUBA-2 and in the CO(3-2) line with HARP at the JCMT. We also retrieved Herschel Hi-GAL data at 70 and 160 micron. The submm continuum emission was decomposed into cores with the algorithm Gaussclumps (Stutzki & Guesten, 1990ApJ...356..513S). By fitting greybodies to the core 4-point SEDs we derived their temperature and mass. Core mass functions were derived in the region more exposed to the FUV flux from massive stars (associated with the HII regions G353.2+0.9, G353.1+0.6, and G353.2+0.7) and in the region less exposed. Table 2 lists the physical properties of the cores in NGC6357.
- ID:
- ivo://CDS.VizieR/J/A+A/515/A55
- Title:
- NGC 6334-NGC 6357 complex
- Short Name:
- J/A+A/515/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our knowledge of high-mass star formation has been mainly based on follow-up studies of bright sources found by IRAS, and has thus been incomplete for its earliest phases, which are inconspicuous at infrared wavelengths. With a new generation of powerful bolometer arrays, unbiased large-scale surveys of nearby high-mass star-forming complexes now search for the high-mass analog of low-mass cores and class 0 protostars. Following the pioneering study of Cygnus X, we investigate the star-forming region NGC 6334-NGC 6357 (~1.7kpc)
- ID:
- ivo://CDS.VizieR/J/A+A/515/A56
- Title:
- NGC 346/N66 JHKs photometry
- Short Name:
- J/A+A/515/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The emission nebula N66 is the brightest HII Region in the Small Magellanic Cloud (SMC), with the stellar association NGC 346 located in its center. The youthfulness of the region NGC 346/N66 is well documented by studies of the gas and dust emission, and the detection in the optical of a rich sample of pre-main sequence (PMS) stars, and in the mid- and far-IR of Young Stellar Objects (YSOs). However, there is a lack of a comprehensive study of this region in the near-IR that will bridge the previous surveys. We perform a photometric analysis on deep, seeing-limited near-IR VLT images of the region NGC 346/N66 and a nearby control field of the SMC in order to locate the centers of active high- and intermediate-mass star formation through the identification of near-IR bright objects as candidate stellar sources under formation. We use archived imaging data obtained with the high-resolution camera ISAAC at VLT of NGC 346/N66 and we construct the near-IR color-magnitude (CMD) and color-color diagrams (C-CD) of all detected sources. We investigate the nature of all stellar populations in the observed CMDs, and we identify all stellar sources that show significant near-IR excess emission in the observed C-CD. We select, thus, the best candidates for being young stellar sources. Results. Based on their near-IR colors we select 263 candidate young stellar sources. This sample comprises a variety of objects such as intermediate-mass PMS and Herbig Ae/Be stars and possibly massive YSOs, providing original near-IR colors for them. The spatial distribution of the selected candidate sources shows that they are located along the dusty filamentary structures of N66 seen in mid- and far-IR dust emission and agrees very well with that of previously detected candidate YSOs and PMS stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/476/2813
- Title:
- NGC 2282 photometry of variable stars
- Short Name:
- J/MNRAS/476/2813
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report here CCD I-band time series photometry of a young (2-5Myr) cluster NGC 2282, in order to identify and understand the variability of pre-main-sequence (PMS) stars. The I-band photometry, down to ~20.5mag, enables us to probe the variability towards the lower mass end (~0.1M_{sun}_) of PMS stars. From the light curves of 1627 stars, we identified 62 new photometric variable candidates. Their association with the region was established from H{alpha} emission and infrared (IR) excess. Among 62 variables, 30 young variables exhibit H{alpha} emission, near-IR (NIR)/mid-IR (MIR) excess or both and are candidate members of the cluster. Out of 62 variables, 41 are periodic variables, with a rotation rate ranging from 0.2-7d. The period distribution exhibits a median period at ~1d, as in many young clusters (e.g. NGC 2264, ONC, etc.), but it follows a unimodal distribution, unlike others that have bimodality, with slow rotators peaking at ~6-8d. To investigate the rotation-disc and variability-disc connection, we derived the NIR excess from {Delta}(I-K) and the MIR excess from Spitzer [3.6]-[4.5]um data. No conclusive evidence of slow rotation with the presence of discs around stars and fast rotation for discless stars is obtained from our periodic variables. A clear increasing trend of the variability amplitude with IR excess is found for all variables.
376. NGC 7538 region YSOs
- ID:
- ivo://CDS.VizieR/J/MNRAS/467/2943
- Title:
- NGC 7538 region YSOs
- Short Name:
- J/MNRAS/467/2943
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Deep optical photometric data on the NGC 7538 region were collected and combined with archival data sets from the Chandra, 2MASS and Spitzer surveys to generate a new catalogue of young stellar objects (YSOs) including those not showing infrared excess emission. This new catalogue is complete down to 0.8M_{sun}_. The nature of the YSOs associated with the NGC 7538 region and their spatial distribution are used to study the star-formation process and the resultant mass function (MF) in the region. Out of the 419 YSOs, ~91 per cent have ages between 0.1 and 2.5Myr and ~86 per cent have masses between 0.5 and 3.5M_{sun}_, as derived by the spectral energy distribution fitting analysis. Around 24, 62 and 2 per cent of these YSOs are classified to be class I, class II and class III sources, respectively. The X-ray activities for the class I, class II and class III objects are not significantly different from each other. This result implies that the enhanced X-ray surface flux due to the increase in the rotation rate may be compensated for by the decrease in the stellar surface area during the pre-main-sequence evolution. Our analysis shows that the O3V type high-mass star IRS 6 may have triggered the formation of young low-mass stars up to a radial distance of 3pc. The MF shows a turn-off at around 1.5M_{sun}_ and the value of its slope {Gamma} in the mass range 1.5<M/M_{sun}_<6 is -1.76+/-0.24, which is steeper than the Salpeter value.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/1993
- Title:
- NGC 1893 stars LSR velocities
- Short Name:
- J/MNRAS/477/1993
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- OB associations are the prevailing star-forming sites in the Galaxy. Up to now, the process of how OB associations were formed remained a mystery. A possible process is self-regulating star formation driven by feedback from massive stars. However, although a number of observational studies uncovered various signposts of feedback-driven star formation, the effectiveness of such feedback has been questioned. Stellar and gas kinematics is a promising tool to capture the relative motion of newborn stars and gas away from ionizing sources. We present high-resolution spectroscopy of stars and gas in the young open cluster NGC 1893. Our findings show that newborn stars and the tadpole nebula Sim 130 are moving away from the central cluster containing two O-type stars, and that the time-scale of sequential star formation is about 1Myr within a 9pc distance. The newborn stars formed by feedback from massive stars account for at least 18 per cent of the total stellar population in the cluster, suggesting that this process can play an important role in the formation of OB associations. These results support the self-regulating star formation model.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A78
- Title:
- NGC6334 850um I, Q, U Stokes parameter maps
- Short Name:
- J/A+A/647/A78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Molecular filaments and hubs have received special attention recently thanks to new studies showing their key role in star formation. While the (column) density and velocity structures of both filaments and hubs have been carefully studied, their magnetic field (B-field) properties have yet to be characterized. Consequently, the role of B-fields in the formation and evolution of hub-filament systems is not well constrained. We aim to understand the role of the B-field and its interplay with turbulence and gravity in the dynamical evolution of the NGC 6334 filament network that harbours cluster-forming hubs and high-mass star formation. We present new observations of the dust polarized emission at 850mum toward the 2pcx10pc map of NGC 6334 at a spatial resolution of 0.09pc obtained with the James Clerk Maxwell Telescope (JCMT) as part of the B-field In STar-forming Region Observations (BISTRO) survey. We study the distribution and dispersion of the polarized intensity (PI), the polarization fraction (PF), and the plane-of-the-sky (POS) B-field angle ({chi}B_POS_) toward the whole region, along the 10pc-long ridge and along the sub-filaments connected to the ridge and the hubs. We derived the power spectra of the intensity and {chi}B_POS_ along the ridge crest and compared them with the results obtained from simulated filaments. The observations span ~3 orders of magnitude in I and PI and ~2 orders of magnitude in PF (from ~0.2% to ~20%). A large scatter in PI and PF is observed for a given value of I. Our analyzes show a complex B-field structure when observed over the whole region (~10pc); however, at smaller scales (~1pc), {chi}B_POS_ varies coherently along the crests of the filament network. The observed power spectrum of {chi}B_POS_ can be well represented with a power law function with a slope of -1.33+/-0.23, which is ~20% shallower than that of I. We find that this result is compatible with the properties of simulated filaments and may indicate the physical processes at play in the formation and evolution of star-forming filaments. Along the sub-filaments, {chi}B_POS_ rotates from being mostly perpendicular or randomly oriented with respect to the crests to mostly parallel as the sub-filaments merge with the ridge and hubs. This variation of the B-field structure along the sub-filaments may be tracing local velocity flows of infalling matter in the ridge and hubs. Our analysis also suggests a variation in the energy balance along the crests of these sub-filaments, from magnetically critical or supercritical at their far ends to magnetically subcritical near the ridge and hubs. We also detect an increase in PF toward the high-column density (N_H2_>~10^23^cm^-2^) star cluster-forming hubs. These latter large PF values may be explained by the increase in grain alignment efficiency due to stellar radiation from the newborn stars, combined with an ordered B-field structure. These observational results reveal for the first time the characteristics of the small-scale (down to ~0.1pc) B-field structure of a 10pc-long hub-filament system. Our analyzes show variations in the polarization properties along the sub-filaments that may be tracing the evolution of their physical properties during their interaction with the ridge and hubs. We also detect an impact of feedback from young high-mass stars on the local B-field structure and the polarization properties, which could put constraints on possible models for dust grain alignment and provide important hints as to the interplay between the star formation activity and interstellar B-fields.
- ID:
- ivo://CDS.VizieR/J/ApJ/581/325
- Title:
- NGC 2071 water masers
- Short Name:
- J/ApJ/581/325
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have mapped the water maser emission associated with the infrared centers IRS 1 and IRS 3 of the NGC 2071 IR star-forming region at four epochs over ~4 months with the Very Long Baseline Array. We detected 269 maser features with ~1km/s line widths and measured 30 proper motions. In each infrared center, the water maser emission appears to trace parts of a protostellar disk and collimated outflow.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A35
- Title:
- NGC 247 young stellar population
- Short Name:
- J/A+A/626/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We seek to investigate the characteristics of the young stellar population in the spiral galaxy NGC 247. In particular, we focused our attention in its hierarchical clustering distributions and the properties of the smallest groups. We used multiband Hubble Space Telescope (HST) data from three fields covering more than half of NGC 247 to select the young population. Then, through the path linkage criterion (PLC), we found compact young star groups and estimated their fundamental parameters, such as their stellar densities, sizes, number of members, and luminosity function (LF) slopes. We also performed a fractal analysis to determinate the clustering properties of this population. We built a stellar density map and dendrograms corresponding to the galactic young population to detect large structures and depict their main characteristics. We detect 339 young star groups, for which we compute a mean radius of ~60pc and a maximum size distribution between 30 and 70pc. We also obtain LF slopes with a bimodal distribution showing peaks at ~0.1 and ~0.2. We identify several candidates for HII regions that follow an excellent spatial correlation with the young groups found by the PLC. We observe that the young populations are hierarchically organized, wherein the smaller and denser structures are within larger and less dense structures. We notice that all these groups present a fractal subclustering, following the hierarchical distribution observed in the corresponding stellar density map. For the large young structures observed in this map, we obtain a fractal dimension of ~1.6-1.8 using the perimeter-area relation and cumulative size distribution. These values are consistent with a scenario of hierarchical star formation.
