- ID:
- ivo://CDS.VizieR/J/ApJ/682/445
- Title:
- Spitzer observations of S254-S258
- Short Name:
- J/ApJ/682/445
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer IRAC, NOAO 2.1m Flamingos, Keck NIRC, and FCRAO SEQUOIA observations of the massive star-forming complex S254-S258, covering an area of 25'x20'. Using a combination of the IRAC and NIR data, we identify and classify the young stellar objects (YSOs) in the complex. We detect 510 sources with near- or mid-IR excess, and we classify 87 Class I and 165 Class II sources. The YSOs are found in clusters surrounded by isolated YSOs in a low-density distributed population. The ratio of clustered to total YSOs is 0.8. We identify six new clusters in the complex. One of them, G192.63-00, is located around the ionizing star of the HII region S255. We hypothesize that the ionizing star of S255 was formed in this cluster. We also detect a southern component of the cluster in HII region S256. The cluster G192.54-0.15, located inside HII region S254 has a V_LSR_ of 17km/s with respect to the main cloud, and we conclude that it is located in the background of the complex. The structure of the molecular cloud is examined using ^12^CO, and ^13^CO, as well as a near-IR extinction map. The main body of the molecular cloud has V_LSR_ between 5 and 9km/s. The arc-shaped structure of the molecular cloud following the border of the HII regions and the high column density in the border of the HII regions support the idea that the material has been swept up by the expansion of the HII regions.
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- ID:
- ivo://CDS.VizieR/J/ApJS/184/18
- Title:
- Spitzer survey of young stellar clusters
- Short Name:
- J/ApJS/184/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a uniform mid-infrared imaging and photometric survey of 36 young, nearby, star-forming clusters and groups using Spitzer IRAC and MIPS. We have confidently identified and classified 2548 young stellar objects (YSOs) using recently established mid-infrared color-based methods. We have devised and applied a new algorithm for the isolation of local surface density enhancements from point source distributions, enabling us to extract the overdense cores of the observed star-forming regions for further analysis. We have compiled several basic structural measurements of these cluster cores from the data, such as mean surface densities of sources, cluster core radii, and aspect ratios, in order to characterize the ranges for these quantities. We find that a typical cluster core is 0.39pc in radius, has 26 members with infrared excess in a ratio of Class II to Class I sources of 3.7, is embedded in a A_Ks_=0.8mag cloud clump, and has a surface density of 60pc^-2^. We examine the nearest neighbor distances among the YSOs in several ways, demonstrating similarity in the spacings between Class II and Class I sources but large member clusters appear more dense than smaller clusters. We demonstrate that near-uniform source spacings in cluster cores are common, suggesting that simple Jeans fragmentation of parsec-scale cloud clumps may be the dominant process governing star formation in nearby clusters and groups. Finally, we compare our results to other similar surveys in the literature and discuss potential biases in the data to guide further interpretation.
- 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.
