- ID:
- ivo://CDS.VizieR/J/A+A/617/A83
- Title:
- MIDI atlas of low- and intermediate-mass YSOs
- Short Name:
- J/A+A/617/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Protoplanetary disks show large diversity regarding their morphology and dust composition. With mid-infrared interferometry the thermal emission of disks can be spatially resolved, and the distribution and properties of the dust within can be studied. Our aim is to perform a statistical analysis on a large sample of 82 disks around low- and intermediate-mass young stars, based on mid-infrared interferometric observations. We intend to study the distribution of disk sizes, variability, and the silicate dust mineralogy. Archival mid-infrared interferometric data from the MIDI instrument on the Very Large Telescope Interferometer are homogeneously reduced and calibrated. Geometric disk models are used to fit the observations to get spatial information about the disks. An automatic spectral decomposition pipeline is applied to analyze the shape of the silicate feature. We present the resulting data products in the form of an atlas, containing N band correlated and total spectra, visibilities, and differential phases. The majority of our data can be well fitted with a continuous disk model, except for a few objects, where a gapped model gives a better match. From the mid-infrared size-luminosity relation we find that disks around T Tauri stars are generally colder and more extended with respect to the stellar luminosity than disks around Herbig Ae stars. We find that in the innermost part of the disks (r<~1au) the silicate feature is generally weaker than in the outer parts, suggesting that in the inner parts the dust is substantially more processed. We analyze stellar multiplicity and find that in two systems (AB Aur and HD 72106) data suggest a new companion or asymmetric inner disk structure. We make predictions for the observability of our objects with the upcoming Multi-AperTure mid- Infrared SpectroScopic Experiment (MATISSE) instrument, supporting the practical preparations of future MATISSE observations of T Tauri stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/445/971
- Title:
- Mid-infrared images of W75N
- Short Name:
- J/A+A/445/971
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An infrared study that includes ground-based mid-infrared images between 8.7 and 18.7um and IRAC images at 3.6, 4.5, 5.8 and 8.0um of the W75 N massive star forming region is presented. The 12.5um image shows the presence of four mid-infrared sources in the region W75 N(B), three of which have bright near-infrared counterparts, IRS 1, IRS 2 and IRS 3, all with significant excess emission at lambda>2.0um. IRS 2 has a steep energy distribution and the computed infrared luminosity is consistent with the presence of a young B3 star. The observed IRAC colors of IRS 3 indicate that this source is a Class II intermediate mass young star, consistent with its infrared energy distribution and luminosity. The fourth, newly discovered, mid-infrared source appears coincident with the ultracompact HII region VLA 3, and is located within the millimeter core MM 1. We derived a luminosity of ~750L_{sun}_ and a visual extinction A_V_~90 for this source. From the IRAC images, we detected 75 sources in an area of 120"x120" centered in W75 N. At least 25 of these sources are associated with the molecular cloud and form a young stellar cluster as shown in the IRAC two-color and the H-Ks versus Ks-[3.6] diagrams.
- ID:
- ivo://CDS.VizieR/J/ApJ/733/50
- Title:
- Mid-IR photometric monitoring of the ONC
- Short Name:
- J/ApJ/733/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present initial results from time-series imaging at infrared wavelengths of 0.9deg^2^ in the Orion Nebula Cluster (ONC). During Fall 2009 we obtained 81 epochs of Spitzer 3.6 and 4.5um data over 40 consecutive days. We extracted light curves with ~3% photometric accuracy for ~2000 ONC members ranging from several solar masses down to well below the hydrogen-burning mass limit. For many of the stars, we also have time-series photometry obtained at optical (Ic) and/or near-infrared (JKs) wavelengths. Our data set can be mined to determine stellar rotation periods, identify new pre-main-sequence eclipsing binaries, search for new substellar Orion members, and help better determine the frequency of circumstellar disks as a function of stellar mass in the ONC. Our primary focus is the unique ability of 3.6 and 4.5um variability information to improve our understanding of inner disk processes and structure in the Class I and II young stellar objects (YSOs). In this paper, we provide a brief overview of the YSOVAR Orion data obtained in Fall 2009 and highlight our light curves for AA-Tau analogs -YSOs with narrow dips in flux, most probably due to disk density structures passing through our line of sight. Detailed follow-up observations are needed in order to better quantify the nature of the obscuring bodies and what this implies for the structure of the inner disks of YSOs.
- ID:
- ivo://CDS.VizieR/J/ApJ/702/1507
- Title:
- Mid-IR photometry in IC 1396A
- Short Name:
- J/ApJ/702/1507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used Spitzer/Infrared Array Camera (IRAC) to conduct a photometric monitoring program of the IC1396A dark globule in order to study the mid-IR (3.6-8um) variability of the heavily embedded young stellar objects (YSOs) present in that area. We obtained light curves covering a 14 day timespan with a twice daily cadence for 69 YSOs, and continuous light curves with approximately 12s cadence over 7hr for 38 YSOs. Typical accuracies for our relative photometry were 1%-2% for the long timespan data and a few millimagnitude, corresponding to less than 0.5%, for the 7hr continuous "staring-mode" data. More than half of the YSOs showed detectable variability, with amplitudes from ~0.05mag to ~0.2mag. One star, IC1396A-47, shows a 3.5hr periodic light curve; this object may be a PMS Delta Scuti star.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/51
- Title:
- Mineralogical compositions of dust grains
- Short Name:
- J/ApJ/734/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mineralogical studies of silicate features emitted by dust grains in protoplanetary disks and solar system bodies can shed light on the progress of planet formation. The significant fraction of crystalline material in comets, chondritic meteorites, and interplanetary dust particles indicates a modification of the almost completely amorphous interstellar medium dust from which they formed. The production of crystalline silicates, thus, must happen in protoplanetary disks, where dust evolves to build planets and planetesimals. Different scenarios have been proposed, but it is still unclear how and when this happens. This paper presents dust grain mineralogy (composition, crystallinity, and grain size distribution) of a complete sample of protoplanetary disks in the young Serpens cluster. These results are compared to those in the young Taurus region and to sources that have retained their protoplanetary disks in the older Upper Scorpius and {eta} Chamaeleontis stellar clusters, using the same analysis technique for all samples. This comparison allows an investigation of the grain mineralogy evolution with time for a total sample of 139 disks. The mean cluster age and disk fraction are used as indicators of the evolutionary stage of the different populations. Our results show that the disks in the different regions have similar distributions of mean grain sizes and crystallinity fractions (~10%-20%) despite the spread in mean ages. Furthermore, there is no evidence of preferential grain sizes for any given disk geometry nor for the mean cluster crystallinity fraction to increase with mean age in the 1-8Myr range. The main implication is that a modest level of crystallinity is established in the disk surface early on (<=1Myr), reaching an equilibrium that is independent of what may be happening in the disk midplane. These results are discussed in the context of planet formation, in comparison with mineralogical results from small bodies in our own solar system.
- ID:
- ivo://CDS.VizieR/J/ApJ/696/471
- Title:
- MIR spectroscopy of NGC 7538 IRS 1
- Short Name:
- J/ApJ/696/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution (R=75000-100000) mid-infrared spectra of the high-mass embedded young star IRS 1 in the NGC 7538 star-forming region. Absorption lines from many rotational states of C_2_H_2_, ^13^C^12^CH_2_, CH_3_, CH_4_, NH_3_, HCN, HNCO, and CS are seen. The gas temperature, column density, covering factor, line width, and Doppler shift for each molecule are derived. All molecules were fit with two velocity components between -54 and -63km/s. We find high column densities (~10^16^cm^-2^) for all the observed molecules compared to values previously reported and present new results for CH_3_ and HNCO. Several physical and chemical models are considered. The favored model involves a nearly edge-on disk around a massive star. Radiation from dust in the inner disk passes through the disk atmosphere, where large molecular column densities can produce the observed absorption line spectrum.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/231
- Title:
- MISFITS survey: HCO+ obs. of Spitzer YSOs
- Short Name:
- J/ApJ/806/231
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an HCO^+^ J=3->2 survey of Class 0+I and Flat SED young stellar objects (YSOs) found in the Gould Belt clouds by surveys with Spitzer. Our goal is to provide a uniform Stage 0+I source indicator for these embedded protostar candidates. We made single point HCO^+^ J=3->2 measurements toward the source positions at the CSO and APEX of 546 YSOs (89% of the Class 0+I + Flat SED sample). Using the criteria from van Kempen et al. (2009, J/A+A/498/167), we classify sources as Stage 0+I or bona fide protostars and find that 84% of detected sources meet the criteria. We recommend a timescale for the evolution of Stage 0+I (embedded protostars) of 0.54Myr. We find significant correlations of HCO^+^ integrated intensity with {alpha} and T_bol_ but not with L_bol_. The detection fraction increases smoothly as a function of {alpha} and L_bol_, while decreasing smoothly with T_bol_. Using the Stage 0+I sources tightens the relation between protostars and high extinction regions of the cloud; 89% of Stage I sources lie in regions with A_V_>8mag. Class 0+I and Flat SED YSOs that are not detected in HCO^+^ have, on average, a factor of ~2 higher T_bol_ and a factor of ~5 lower L_bol_than YSOs with HCO^+^ detections. We find less YSO contamination, defined as the number of undetected YSOs divided by the total number surveyed, for sources with T_bol_<~600K and L_bol_>~1L_{sun}_. The contamination percentage is >90% at A_V_<4mag and decreases as A_V_ increases.
- ID:
- ivo://CDS.VizieR/J/A+A/533/A121
- Title:
- Missing low-mass stars in S254-S258
- Short Name:
- J/A+A/533/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this study was to find an explanation for the remarkable morphology of the central part of the S254-S258 star forming complex. We performed a deep Chandra X-ray observation of the S254-S258 region in order to efficiently discriminate young stars (with and without circumstellar matter) from the numerous older field stars in the area. We detected 364 X-ray point sources in a 17'x17' field. This X-ray catalog provides, for the first time, a complete sample of all young stars in the region down to about 0.5M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/A+A/604/A78
- Title:
- M17 massive pms stars X-shooter spectra
- Short Name:
- J/A+A/604/A78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation process of massive stars is still poorly understood. Massive young stellar objects (mYSOs) are deeply embedded in their parental clouds; these objects are rare, and thus typically distant, and their reddened spectra usually preclude the determination of their photospheric parameters. M17 is one of the best-studied HII regions in the sky, is relatively nearby, and hosts a young stellar population. We have obtained optical to near-infrared spectra of previously identified candidate mYSOs and a few OB stars in this region with X-shooter on the ESO Very Large Telescope. The large wavelength coverage enables a detailed spectroscopic analysis of the photospheres and circumstellar disks of these candidate mYSOs. We confirm the pre-main-sequence (PMS) nature of six of the stars and characterise the O stars. The PMS stars have radii that are consistent with being contracting towards the main sequence and are surrounded by a remnant accretion disk. The observed infrared excess and the double-peaked emission lines provide an opportunity to measure structured velocity profiles in the disks. We compare the observed properties of this unique sample of young massive stars with evolutionary tracks of massive protostars and propose that these mYSOs near the western edge of the HII region are on their way to become main-sequence stars (~6-20M_{sun}_) after having undergone high mass accretion rates (dMacc/dt~10^-4^-10^-3^M_{sun}_/yr) Their spin distribution upon arrival at the zero age main-sequence (ZAMS) is consistent with that observed for young B stars, assuming conservation of angular momentum and homologous contraction.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/171
- Title:
- mm point sources in the extended Sgr B2 cloud
- Short Name:
- J/ApJ/853/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report ALMA observations with resolution ~0.5" at 3mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000au. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact HII regions and young stellar objects (YSOs). Most of the newly detected sources are YSOs with gas envelopes that, based on their luminosities, must contain objects with stellar masses M*>~8M_{sun}_. Their spatial distribution spread over a ~12x3pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated "starburst" within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density (N(H_2_)>~2x10^23^cm^-2^), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear {Sigma}_*_-{Sigma}_gas_ relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds.
