- ID:
- ivo://CDS.VizieR/J/ApJ/691/672
- Title:
- Spectrocopy of YSOs in Serpens molecular cloud
- Short Name:
- J/ApJ/691/672
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the results of an optical spectroscopic survey designed to confirm the youth and determine the spectral types among a sample of young stellar object (YSO) candidates in the Serpens molecular cloud. We observed 150 infrared (IR) excess objects previously discovered by the Spitzer Legacy Program "From Molecular Cores to Planet-Forming Disks" (c2d), bright enough for subsequent Spitzer/InfraRed Spectrograph (IRS) spectroscopy. We obtained 78 optical spectra of sufficient signal-to-noise for analysis. Extinctions, effective temperatures, and luminosities are estimated for this sample, and used to construct Hertzsprung-Russell (H-R) diagrams for the population. We identified 20 background giants contaminating the sample, based on their relatively high extinction, position in the H-R diagram, the lack of H{alpha} emission and relatively low IR excess. Such strong background contamination (25%) is consistent with the location of Serpens being close to the Galactic plane (5{deg} Galactic latitude). The remaining 58 stars (75%) were all confirmed to be young, mostly K- and M-type stars that are presumed to belong to the cloud. Our analysis shows that the majority of the IR excess objects detected in Serpens are actively accreting, young T-Tauri stars.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/149/103
- Title:
- Spectroscopy of candidate YSOs in Serpens
- Short Name:
- J/AJ/149/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have completed an optical spectroscopic survey of a sample of candidate young stars in the Serpens Main star-forming region selected from deep B, V, and R band images. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys have been biased toward particular stages of pre-main sequence evolution. We have obtained over 700 moderate resolution optical spectra that, when combined with published data, have led to the identification of 63 association members based on the presence of H{alpha} in emission, lithium absorption, X-ray emission, a mid-infrared excess, and/or reflection nebulosity. Twelve YSOs are identified based on the presence of lithium absorption alone. An additional 16 objects are classified as possible association members and their pre-main sequence nature is in need of confirmation. Spectral types along with V and R band photometry were used to derive effective temperatures and bolometric luminosities for association members to compare with theoretical tracks and isochrones for pre-main sequence stars. An average age of 2Myr is derived for this population. When compared to simulations, there is no obvious evidence for an age spread when considering the major sources of uncertainties in the derived luminosities. However when compared to the young cluster in Ophiuchus, the association members in Serpens appear to have a larger spread in luminosities and hence ages which could be intrinsic to the region or the result of a foreground population of YSOs associated with the Aquila Rift. Modeling of the spectral energy distributions from optical through mid-infrared wavelengths has revealed three new transition disk objects, making a total of six in the cluster. Echelle spectra for a subset of these sources enabled estimates of vsini for seven association members. Analysis of gravity-sensitive lines in the echelle and moderate resolution spectra of the association members indicate surface gravities consistent with dwarf or sub-giant stars.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A125
- Title:
- Spiral structure of the Milky Way
- Short Name:
- J/A+A/569/A125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have updated the catalogs of Galactic HII regions, giant molecular clouds (GMCs), and 6.7-GHz methanol masers to outline the spiral structure of our Galaxy. The related parameters have been collected and (re)calculated based on the data in the literature. In particular, for each spiral tracer, we list the photometric or trigonometric distance, and/or the solutions of the kinematic distance ambiguity (KDA) when available. The kinematic distances when adopted are calculated using a flat rotation curve with two sets of R_0_, {Theta}_0_, and solar motions, where one set is the IAU standard and the other is from the new observational results. The rotation curve of Brand & Blitz (1993, Cat. J/A+A/275/67) is also used to derive the kinematic distances.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A79
- Title:
- SPIRE 250um maps of 4 molecular clouds
- Short Name:
- J/A+A/575/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Column-density maps of molecular clouds are one of the most important observables in the context of molecular cloud- and starformation (SF) studies. With the Herschel satellite it is now possible to precisely determine the column density from dust emission, which is the best tracer of the bulk of material in molecular clouds. However, line-of-sight (LOS) contamination from fore- or background clouds can lead to overestimating the dust emission of molecular clouds, in particular for distant clouds. This implies values that are too high for column density and mass, which can potentially lead to an incorrect physical interpretation of the column density probability distribution function (PDF). In this paper, we use observations and simulations to demonstrate how LOS contamination affects the PDF. We apply a first-order approximation (removing a constant level) to the molecular clouds of Auriga and Maddalena (low-mass star-forming), and Carina and NGC3603 (both high-mass SF regions).
- ID:
- ivo://CDS.VizieR/J/ApJ/778/96
- Title:
- Spitzer and NEWFIRM observations of NGC 6334
- Short Name:
- J/ApJ/778/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents a study of the rate and efficiency of star formation in the NGC 6334 star-forming region. We obtained observations at J, H, and K_s_ taken with the NOAO Extremely Wide-Field Infrared Imager and combined them with observations taken with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope at wavelengths = 3.6, 4.5, 5.8, and 8.0{mu}m. We also analyzed previous observations taken at 24{mu}m using the Spitzer MIPS camera as part of the MIPSGAL survey. We have produced a point source catalog with >700000 entries. We have identified 2283 young stellar object (YSO) candidates, 375 Class I YSOs, and 1908 Class II YSOs using a combination of existing IRAC-based color classification schemes that we have extended and validated to the near-IR for use with warm Spitzer data. We have identified multiple new sites of ongoing star formation activity along filamentary structures extending tens of parsecs beyond the central molecular ridge of NGC 6334. By mapping the extinction, we derived an estimate for the gas mass, 2.2x10^5^M_{sun}_. The heavy concentration of protostars along the dense filamentary structures indicates that NGC 6334 may be undergoing a "mini-starburst" event with {Sigma}_SFR_>8.2M_{sun}_M/yr/pc2 and SFE>0.10. We have used these estimates to place NGC 6334 in the Kennicutt-Schmidt diagram to help bridge the gap between observations of local low-mass star-forming regions and star formation in other galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJS/177/551
- Title:
- Spitzer c2d survey of Lupus dark clouds
- Short Name:
- J/ApJS/177/551
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present c2d Spitzer IRAC observations of the Lupus I, III, and IV dark clouds and discuss them in combination with optical, near-infrared, and c2d MIPS data. With the Spitzer data, the new sample contains 159 stars, 4 times larger than the previous one. It is dominated by low- and very low mass stars, and it is complete down to M~0.1M_{sun}_. We find 30%-40% binaries with separations between 100 and 2000AU with no apparent effect on the disk properties of the members. A large majority of the objects are Class II or III objects, with only 20(12%) Class I or flat-spectrum sources. The disk sample is complete down to "debris"-like systems in stars as small as M~0.2M_{sun}_ and includes substellar objects with larger IR excesses. The disk fraction in Lupus is 70%-80%, consistent with an age of 1-2Myr. However, the young population contains 20% optically thick accretion disks and 40% relatively less flared disks. A growing variety of inner disk structures is found for larger inner disk clearings for equal disk masses.
- ID:
- ivo://CDS.VizieR/J/ApJ/767/147
- Title:
- Spitzer-IRAC photometry of jets in Vela-D
- Short Name:
- J/ApJ/767/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of H_2_ jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer-IRAC data between 3.6 {mu}m and 8.0 {mu}m. Our search has led to the identification of 15 jets (two new discoveries) and about 70 well-aligned knots within 1.2 deg^2^. We compare the Infrared Array Camera (IRAC) maps with observations of the H_2_ 1-0 S(1) line at 2.12 {mu}m, with a Spitzer-MIPS map at 24 {mu}m and 70 {mu}m, and with a map of the dust continuum emission at 1.2 mm. From such a comparison, we find a tight association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalog of the young stellar objects of VMR-D. In particular, we searched for all the sources of Class II or (preferentially) earlier which are located close to the jet center and aligned with it. Furthermore, the association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets, for which two alternative candidates are given. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 {mu}m, suggesting that they are very young protostars. Three of them are also associated with the most compact jets (projected length<~0.1 pc). The exciting source spectral energy distributions (SEDs) have been constructed and modeled by means of all the available photometric data between 1.2 {mu}m and 1.2 mm. From SEDs fits, we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24]-[70] color, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.
518. Spitzer IRDCs
- ID:
- ivo://CDS.VizieR/J/ApJ/698/324
- Title:
- Spitzer IRDCs
- Short Name:
- J/ApJ/698/324
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a survey of a sample of infrared-dark clouds (IRDCs) with the Spitzer Space Telescope in order to explore their mass distribution. We present a method for tracing mass using dust absorption against the bright Galactic background at 8um. The IRDCs in this sample are comprised of tens of clumps, ranging in sizes from 0.02 to 0.3pc in diameter and masses from 0.5 to a few 10^3^M_{sun}_, the broadest dynamic range in any clump mass spectrum study to date.
- ID:
- ivo://CDS.VizieR/J/ApJ/762/128
- Title:
- Spitzer/IRS disk parameters in Serpens
- Short Name:
- J/ApJ/762/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral energy distributions are presented for 94 young stars surrounded by disks in the Serpens Molecular Cloud, based on photometry and Spitzer/IRS spectra. Most of the stars have spectroscopically determined spectral types. Taking a distance to the cloud of 415pc rather than 259pc, the distribution of ages is shifted to lower values, in the 1-3Myr range, with a tail up to 10Myr. The mass distribution spans 0.2-1.2M_{sun}_, with median mass of 0.7M_{sun}_. The distribution of fractional disk luminosities in Serpens resembles that of the young Taurus Molecular Cloud, with most disks consistent with optically thick, passively irradiated disks in a variety of disk geometries (L_disk_/L_star_~0.1). In contrast, the distributions for the older Upper Scorpius and {eta} Chamaeleontis clusters are dominated by optically thin lower luminosity disks (L_disk_/L_star_~0.02). This evolution in fractional disk luminosities is concurrent with that of disk fractions: with time disks become fainter and the disk fractions decrease. The actively accreting and non-accreting stars (based on H{alpha} data) in Serpens show very similar distributions in fractional disk luminosities, differing only in the brighter tail dominated by strongly accreting stars. In contrast with a sample of Herbig Ae/Be stars, the T Tauri stars in Serpens do not have a clear separation in fractional disk luminosities for different disk geometries: both flared and flat disks present wider, overlapping distributions. This result is consistent with previous suggestions of a faster evolution for disks around Herbig Ae/Be stars. Furthermore, the results for the mineralogy of the dust in the disk surface (grain sizes, temperatures and crystallinity fractions, as derived from Spitzer/IRS spectra) do not show any correlation to either stellar and disk characteristics or mean cluster age in the 1-10Myr range probed here. A possible explanation for the lack of correlation is that the processes affecting the dust within disks have short timescales, happening repeatedly, making it difficult to distinguish long-lasting evolutionary effects.
- ID:
- ivo://CDS.VizieR/J/AJ/144/31
- Title:
- Spitzer+2MASS photometry of protostar candidates
- Short Name:
- J/AJ/144/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24{mu}m spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24{mu}m), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1L_{sun}_ and show a tail extending toward luminosities above 100L_{sun}_. The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1L_{sun}_. Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity functions to those predicted by models and find that our observed luminosity functions are best matched by models that invoke competitive accretion, although we do not find strong agreement between the high-mass SF clouds and any of the models.
