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31. Vienna survey in Orion. III.
ID:
ivo://CDS.VizieR/J/A+A/622/A149
Title:
Vienna survey in Orion. III.
Short Name:
J/A+A/622/A149
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have extended and refined the existing young stellar object (YSO) catalogs for the Orion A molecular cloud, the closest massive star-forming region to Earth. This updated catalog is driven by the large spatial coverage (18.3deg^2^, ~950pc^2^), seeing limited resolution (~0.7''), and sensitivity (K_s_<19mag) of the ESO-VISTA near-infrared survey of the Orion A cloud (VISION). Combined with archival mid- to far-infrared data, the VISTA data allow for a refined and more robust source selection. We estimate that among previously known protostars and pre-main-sequence stars with disks, source contamination levels (false positives) are at least ~6.4% and ~2.3%, respectively, mostly due to background galaxies and nebulosities. We identify 274 new YSO candidates using VISTA/Spitzer based selections within previously analyzed regions, and VISTA/WISE based selections to add sources in the surroundings, beyond previously analyzed regions. The WISE selection method recovers about 59% of the known YSOs in Orion A's low-mass star-forming part L1641, which shows what can be achieved by the all-sky WISE survey in combination with deep near-infrared data in regions without the influence of massive stars. The new catalog contains 2980 YSOs, which were classified based on the de-reddened mid-infrared spectral index into 188 protostars, 185 flat-spectrum sources, and 2607 pre-main-sequence stars with circumstellar disks. We find a statistically significant difference in the spatial distribution of the three evolutionary classes with respect to regions of high dust column-density, confirming that flat-spectrum sources are at a younger evolutionary phase compared to Class IIs, and are not a sub-sample seen at particular viewing angles.
32. VVV high amplitude NIR variable stars
ID:
ivo://CDS.VizieR/J/MNRAS/465/3011
Title:
VVV high amplitude NIR variable stars
Short Name:
J/MNRAS/465/3011
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the discovery of 816 high-amplitude infrared variable stars ({Delta}K_s_>1mag) in 119deg^2^ of the Galactic mid-plane covered by the VISTA Variables in the Via Lactea (VVV) survey. Almost all are new discoveries and about 50 per cent are young stellar objects (YSOs). This provides further evidence that YSOs are the commonest high-amplitude infrared variable stars in the Galactic plane. In the 2010-2014 time series of likely YSOs, we find that the amplitude of variability increases towards younger evolutionary classes (class I and flat-spectrum sources) except on short time-scales (<25d) where this trend is reversed. Dividing the likely YSOs by light-curve morphology, we find 106 with eruptive light curves, 45 dippers, 39 faders, 24 eclipsing binaries, 65 long-term periodic variables (P>100d) and 162 short-term variables. Eruptive YSOs and faders tend to have the highest amplitudes and eruptive systems have the reddest spectral energy distribution (SEDs). Follow-up spectroscopy in a companion paper verifies high accretion rates in the eruptive systems. Variable extinction is disfavoured by the two epochs of colour data. These discoveries increase the number of eruptive variable YSOs by a factor of at least 5, most being at earlier stages of evolution than the known FUor and EXor types. We find that eruptive variability is at least an order of magnitude more common in class I YSOs than class II YSOs. Typical outburst durations are 1-4yr, between those of EXors and FUors. They occur in 3-6 per cent of class I YSOs over a 4yr time span.
33. Young clumps embedded in IRDC
ID:
ivo://CDS.VizieR/J/MNRAS/451/3089
Title:
Young clumps embedded in IRDC
Short Name:
J/MNRAS/451/3089
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalogue of starless and protostellar clumps associated with infrared dark clouds (IRDCs) in a 40 degrees wide region of the inner Galactic plane (|b|<=1). We have extracted the far-infrared (FIR) counterparts of 3493 IRDCs with known distance in the Galactic longitude range 15<=l<=55 and searched for the young clumps using Herschel infrared Galactic plane survey, the survey of the Galactic plane carried out with the Herschel satellite. Each clump is identified as a compact source detected at 160, 250 and 350um. The clumps have been classified as protostellar or starless, based on their emission (or lack of emission) at 70um. We identify 1723 clumps, 1056 (61%) of which are protostellar and 667 (39%) starless. These clumps are found within 764 different IRDCs, 375 (49%) of which are only associated with protostellar clumps, 178 (23%) only with starless clumps, and 211 (28%) with both categories of clumps. The clumps have a median mass of ~250M_{sun}_ and range up to >10^4^M_{sun}_ in mass and up to 10^5^L_{sun}_ in luminosity. The mass-radius distribution shows that almost 30% of the starless clumps identified in this survey could form high-mass stars; however these massive clumps are confined in only 4% of the IRDCs. Assuming a minimum mass surface density threshold for the formation of high-mass stars, the comparison of the numbers of massive starless clumps and those already containing embedded sources suggests an upper limit lifetime for the starless phase of ~10^5^yr for clumps with a mass M>500M_{sun}_.
34. Youngest massive protostars in the LMC
ID:
ivo://CDS.VizieR/J/A+A/518/L73
Title:
Youngest massive protostars in the LMC
Short Name:
J/A+A/518/L73
Date:
21 Oct 2021
Publisher:
CDS
Description:
We demonstrate the unique capabilities of Herschel to study very young luminous extragalactic young stellar objects (YSOs) by analyzing a central strip of the Large Magellanic Cloud obtained through the HERITAGE Science Demonstration Program. We combine PACS 100 and 160, and SPIRE 250, 350, and 500um photometry with 2MASS (1.25-2.17um) and Spitzer IRAC and MIPS (3.6-70um) to construct complete spectral energy distributions (SEDs) of compact sources. From these, we identify 207 candidate embedded YSOs in the observed region, ~40% never-before identified. We discuss their position in far-infrared color-magnitude space, comparing with previously studied, spectroscopically confirmed YSOs and maser emission. All have red colors indicating massive cool envelopes and great youth. We analyze four example YSOs, determining their physical properties by fitting their SEDs with radiative transfer models. Fitting full SEDs including the Herschel data requires us to increase the size and mass of envelopes included in the models. This implies higher accretion rates (greater or equal to 10^-4^M_{sun}_/yr), in agreement with previous outflow studies of high-mass protostars. Our results show that Herschel provides reliable longwave SEDs of large samples of high-mass YSOs; discovers the youngest YSOs whose SEDs peak in Herschel bands; and constrains the physical properties and evolutionary stages of YSOs more precisely than was previously possible.

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