- ID:
- ivo://CDS.VizieR/J/A+A/507/1485
- Title:
- Young (proto)stellar population in L1630
- Short Name:
- J/A+A/507/1485
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the young (proto)stellar population in NGC 2023 and the L 1630 molecular cloud bordering the H II region IC 434, using Spitzer IRAC and MIPS archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA observations of one of the Class 0 protostars, NGC 2023 MM 1. We study the distribution of gas, dust and young stars in this region to see where stars are forming, whether the expansion of the H II region has triggered star formation, and whether dense cold cores have already formed stars. We have performed photometry of all IRAC and MIPS images, and used color-color diagrams to identify and classify all young stars seen within a 22'x26' field along the boundary between IC 434 and L 1630.
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- ID:
- ivo://CDS.VizieR/J/ApJ/770/1
- Title:
- YSO candidates in G38.9-0.4 region
- Short Name:
- J/ApJ/770/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the star formation (SF) region G38.9-0.4 using publicly available multiwavelength Galactic plane surveys from ground- and space-based observatories. This region is composed of four bright mid-IR bubbles and numerous infrared dark clouds. Two bubbles, N 74 and N 75, each host a star cluster anchored by a single O9.5V star. We identified 162 young stellar objects (YSOs) and classify 54 as stage I, 7 as stage II, 6 as stage III, and 32 as ambiguous. We do not detect the classical signposts of triggered SF, i.e., star-forming pillars or YSOs embedded within bubble rims. We conclude that feedback-triggered SF has not occurred in G38.9-0.4. The YSOs are preferentially coincident with infrared dark clouds. This leads to a strong correlation between areal YSO mass surface density and gas mass surface density with a power law slope near 1.3, which closely matches the Schmidt-Kennicutt Law. The correlation is similar inside and outside the bubbles and may mean that the SF efficiency is neither enhanced nor suppressed in regions potentially influenced by stellar feedback. This suggests that gas density, regardless of how it is collected, is a more important driver of SF than stellar feedback. Larger studies should be able to quantify the fraction of all SF that is feedback-triggered by determining the fraction SF, feedback-compressed gas surrounding H II regions relative to that already present in molecular clouds.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/95
- Title:
- YSO candidates within 5' from the IR bubble N4
- Short Name:
- J/ApJ/818/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The physical mechanisms that induce the transformation of a certain mass of gas in new stars are far from being well understood. Infrared bubbles associated with H II regions have been considered to be good samples for investigating triggered star formation. In this paper we report on the investigation of the dust properties of the infrared bubble N4 around the H II region G11.898+0.747, analyzing its interaction with its surroundings and star formation histories therein, with the aim of determining the possibility of star formation triggered by the expansion of the bubble. Using Herschel PACS and SPIRE images with a wide wavelength coverage, we reveal the dust properties over the entire bubble. Meanwhile, we are able to identify six dust clumps surrounding the bubble, with a mean size of 0.50pc, temperature of about 22K, mean column density of 1.7x10^22^/cm2, mean volume density of about 4.4x10^4^/cm3, and a mean mass of 320M_{sun}_. In addition, from PAH emission seen at 8 {mu}m, free-free emission detected at 20cm, and a probability density function in special regions, we could identify clear signatures of the influence of the HII region on the surroundings. There are hints of star formation, though further investigation is required to demonstrate that N4 is the triggering source.
- ID:
- ivo://CDS.VizieR/J/AJ/144/173
- Title:
- YSOs from SED fitting in six HII regions
- Short Name:
- J/AJ/144/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigated six HII regions with infrared, bright rimmed bubble or cometary morphology, in search of quantitative evidence for triggered star formation, both collect and collapse and radiatively driven implosion (RDI). We identified and classified 458 young stellar objects (YSOs) in and around the HII regions. YSOs were determined by fitting a collection of radiative transfer model spectral energy distributions to infrared photometry for a large sample of point sources. We determined areas where there exist enhanced populations of relatively unevolved YSOs on the bright rims of these regions, suggesting that star formation has been triggered there. We further investigated the physical properties of the regions by using radio continuum emission as a proxy for ionizing flux powering the HII regions, and ^13^CO(1-0) observations to measure masses and gravitational stability of molecular clumps. We used an analytical model of collect and collapse triggered star formation, as well as a simulation of RDI, and thus we compare the observed properties of the molecular gas with those predicted in the triggering scenarios. Notably, those regions in our sample that show evidence of cometary, or "blister", morphology are more likely to show evidence of triggering.
505. YSOs in N63 and N180
- ID:
- ivo://CDS.VizieR/J/ApJ/678/200
- Title:
- YSOs in N63 and N180
- Short Name:
- J/ApJ/678/200
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used Spitzer infrared observations to find the young stars of two HII regions in the Large Magellanic Cloud, N63 and N180. The young stellar object (YSO) candidates were identified in each nebula by means of color-color, color-magnitude diagrams, and the shapes of their spectral energy distributions (SEDs). The most luminous YSOs are found near the ionization fronts within strong 8um emission clumps. Most YSOs, less luminous, are seen in projection inside the HII regions. HST images show several Class I stars that have emerged along the borders of the HII regions; other YSOs are embedded in cometary clouds. The most luminous YSO of N63 is connected to a string of pointlike sources. Its SED can be modeled by a central source of stellar mass M_*_ between 7 and 11M_{sun}_, with a circumstellar disk of outer radius R_d_ of ~55AU, and an envelope of moderate accretion rate, M_env_ of ~2x10^-5^M_{sun}_/yr. N180 is experiencing a phase of star formation more intense than N63, attested by the properties of its most luminous YSO: M_*_ of 25M_{sun}_, R_d_ of ~200AU, and M_env_ of ~1.5x10^-3^M_{sun}_/yr. The modes of triggered star formation in N63 and N180 appear similar to those seen in Galactic HII regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/759/48
- Title:
- YSOs in the Galactic HII region Sh2-297
- Short Name:
- J/ApJ/759/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multiwavelength study of the Galactic H II region Sh2-297, located in the Canis Major OB1 complex. Optical spectroscopic observations are used to constrain the spectral type of ionizing star HD 53623 as B0V. The classical nature of this H II region is affirmed by the low values of electron density and emission measure, which are calculated to be 756/cm3 and 9.15x10^5^cm^-6^pc using the radio continuum observations at 610 and 1280MHz, and Very Large Array archival data at 1420MHz. To understand local star formation, we identified the young stellar object (YSO) candidates in a region of area ~7.5'x7.5' centered on Sh2-297 using grism slitless spectroscopy (to identify the H{alpha} emission line stars), and near infrared (NIR) observations. NIR YSO candidates are further classified into various evolutionary stages using color-color and color-magnitude (CM) diagrams, giving 50 red sources (H-K>0.6) and 26 Class II-like sources. The mass and age range of the YSOs are estimated to be ~0.1-2M_{sun}_ and 0.5-2Myr using optical (V/V-I) and NIR (J/J-H) CM diagrams. The mean age of the YSOs is found to be ~1Myr, which is of the order of dynamical age of 1.07Myr of the H II region. Using the estimated range of visual extinction (1.1-25mag) from literature and NIR data for the region, spectral energy distribution models have been implemented for selected YSOs which show masses and ages to be consistent with estimated values. The spatial distribution of YSOs shows an evolutionary sequence, suggesting triggered star formation in the region. The star formation seems to have propagated from the ionizing star toward the cold dark cloud LDN1657A located west of Sh2-297.
- ID:
- ivo://CDS.VizieR/J/ApJ/721/357
- Title:
- YSOs in the LMC star-forming region N206
- Short Name:
- J/ApJ/721/357
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0um and MIPS 24um), Infrared Survey Facility near-infrared survey (J, H, Ks), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36-24um. Young stellar object (YSO) candidates are identified based upon their location in infrared color-magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of ~14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is ~520M_{sun}_. We calculate a current star formation rate of 0.27x10^-1^M_{sun}_/yr/kpc^2^. The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.
- ID:
- ivo://CDS.VizieR/J/ApJ/712/797
- Title:
- YSOs in Vul OB1 association
- Short Name:
- J/ApJ/712/797
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Vulpecula OB association, Vul OB1, is a region of active star formation located in the Galactic plane at 2.3kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of Vul OB1, and search for signatures of past triggering events. We make a census of young stellar objects (YSOs) in Vul OB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in Vul OB1 is rather homogeneous -ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be ~8%. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/432/3445
- Title:
- YSOs on HII complex Sh2-252
- Short Name:
- J/MNRAS/432/3445
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The optically bright, extended HII region Sh2-252 is a part of the Gemini OB1 association. This region is mainly composed of two small clusters NGC 2175s and Teu 136 and four CHII regions namely A, B, C and E. In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population, its characteristics, spatial distribution, morphology of the region and finally to understand the star formation scenario of the complex for the first time. Spitzer-IRAC, MIPS photometry (3.6-24um) are combined with 2MASS-NIR and optical data sets to identify and classify the YSOs by their IR excess emission from their circumstellar material. From the well-fit models for each source derived from the SED fitting tool, we calculated the {chi}^2^ weighted model parameters such as the stellar mass (M*), temperature (T*), stellar age (t*), mass of the disc (Mdisc), disc accretion rate (dMdisc/dt), envelope accretion rate (dMenv/dt) presented in table1.dat.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/20
- Title:
- YSOs population of Sh2-294 with Spitzer/IRAC
- Short Name:
- J/ApJ/755/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sh2-294 H II region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in this region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 H II region at 3.6, 4.5, 5.8, and 8.0{mu}m observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H_2_(2.12{mu}m) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II, and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the H II region and associated with enhanced H_2_emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (<4 M_{sun}_) YSOs; however, we also detected a massive YSO (~9 M_{sun}_) of Class I nature, embedded in a cloud of visual extinction of ~24 mag.
