- ID:
- ivo://CDS.VizieR/J/AJ/157/112
- Title:
- Infrared photometry of YSOs in the W4 cloud complex
- Short Name:
- J/AJ/157/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well known that most of the stars form in rich clusters. However, recent Spitzer observations have shown that a significant number of stars also form in the distributed mode; their origin is not well understood. In this work, we aim to investigate clustered and distributed modes of star formation in the W4 complex. To do so, we identified and characterized the young stellar population associated with the region using homogeneous infrared data sets obtained from the Two Micron All Sky Survey, GLIMPSE, MIPS, and Wide-field Infrared Survey Explorer surveys. We make stellar surface density and minimum spanning tree maps to identify young clusters, and use Spitzer images to identify irradiated structures, such as elephant-trunk-like structures (ETLSs) and pillars in the region. The surface density distribution of the young stellar objects (YSOs) reveals three new clusterings and ~50% distributed protostars in the H II region. The clusters are of low-mass nature but significantly younger than the central cluster IC 1805. We identified ~38 ETLSs in the region, a majority of which consist of one or a few stars at their tips. We find that these stars are low-mass (<2 M_{sun}_) YSOs, located at the outskirts (>17 pc) of the cluster IC 1805 and are part of the scattered distributed population. We argued that the star formation in the ETLSs of W4 is going on possibly due to the triggering effect of the expanding W4 bubble. Although high-resolution photometric and spectroscopic data would be required to confirm the scenario, nonetheless, we discuss the implications of this scenario for our understanding of distributed low-mass star formation in cloud complexes as opposed to other mechanisms such as turbulent fragmentation and dynamical ejection.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/463/175
- Title:
- Infrared study of IRAS 14416-5937 region
- Short Name:
- J/A+A/463/175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out an infrared study of the southern Galactic massive star-forming region associated with IRAS 14416-5937. This star-forming region has been mapped simultaneously in two far infrared bands at ~150 & 210 micron using the TIFR 1-m balloon borne telescope with ~1' angular resolution. We have used the 2MASS JHKs data as well as the GLIMPSE-Spitzer data of this region to study the stellar populations of the embedded young cluster. This region comprises of two sources designated as A and B, separated by ~2pc. The spectrum of a region located close to the source A obtained using the Long Wavelength Spectrometer (LWS) on-board the Infrared Space Observatory (ISO) is presented. Emission from warm dust and the unidentified infrared bands (UIBs) is estimated using the mid-infrared data from the MSX survey. The spatial distribution of the temperature of cool dust and optical depth at 200 micron have been obtained taking advantage of the similar beams in the two TIFR bands. A number of atomic fine structure lines have been detected in the ISO-LWS spectrum, which have been used to estimate the electron density and the effective temperature of the ionising radiation in this region. From the near and mid infrared images, we identify a dust lane due north-west direction of the source A. The dust lane is populated by Class I type sources. Class II type sources are found further along the dust lane as well as below it. Self consistent radiative transfer models of the two sources (A and B) are in good agreement with the observed spectral energy distributions. The spatial distribution of young stellar objects in and around the dust lane suggests that active star formation is taking place along the dust lane and is possibly triggered by the expanding HII regions of A and B.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/125
- Title:
- IN-SYNC. I. APOGEE stellar parameters
- Short Name:
- J/ApJ/794/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Over two years, 8859 high-resolution H-band spectra of 3493 young (1-10Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition, we present accurate extinctions by measuring the E(J-H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally, we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely, the extinction-corrected J-band magnitude, the surface gravity, and the Rsini from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger Rsini than fainter stars at the same effective temperature.
- ID:
- ivo://CDS.VizieR/J/ApJ/799/136
- Title:
- IN-SYNC. II. Candidate young stars in NGC 1333
- Short Name:
- J/ApJ/799/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2Myr) stars in NGC 1333 is 0.92+/-0.12km/s after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a subvirial velocity dispersion of 0.5km/s. Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70{mu}G magnetic field acting on the dense cores or be the signature of a cluster with initial substructure undergoing global collapse.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/59
- Title:
- IN-SYNC. IV. YSOs in Orion A
- Short Name:
- J/ApJ/818/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the Sloan Digital Sky Survey APOGEE INfrared Spectroscopy of Young Nebulous Clusters program (IN-SYNC) survey of the Orion A molecular cloud. This survey obtained high-resolution near-infrared spectroscopy of about 2700 young pre-main-sequence stars on a ~6{deg} field of view. We have measured accurate stellar parameters (T_eff_, logg, vsini) and extinctions and placed the sources in the Hertzsprung-Russel diagram (HRD). We have also extracted radial velocities for the kinematic characterization of the population. We compare our measurements with literature results to assess the performance and accuracy of the survey. Source extinction shows evidence for dust grains that are larger than those in the diffuse interstellar medium: we estimate an average R_V_=5.5 in the region. Importantly, we find a clear correlation between HRD inferred ages and spectroscopic surface-gravity-inferred ages and between extinction and disk presence; this strongly suggests a real spread of ages larger than a few Myr. Focusing on the young population around NGC 1980/{iota} Ori, which has previously been suggested to be a separate, foreground, older cluster, we confirm its older (~5Myr) age and low A_V_, but considering that its radial velocity distribution is indistinguishable from Orion A's population, we suggest that NGC 1980 is part of Orion A's star formation activity. Based on their stellar parameters and kinematic properties, we identify 383 new candidate members of Orion A, most of which are diskless sources in areas of the region poorly studied by previous works.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/72
- Title:
- IN-SYNC. VIII. YSOs in NGC 1333, IC 348 and Orion A
- Short Name:
- J/ApJ/869/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we address two issues related to primordial disk evolution in three clusters (NGC1333, IC348, and OrionA) observed by the INfrared Spectra of Young Nebulous Clusters (IN-SYNC) project. First, in each cluster, averaged over the spread of age, we investigate how disk lifetime is dependent on stellar mass. The general relation in IC348 and OrionA is that primordial disks around intermediate-mass stars (2-5M_{sun}_) evolve faster than those around loss-mass stars (0.1-1M_{sun}_), which is consistent with previous results. However, considering only low-mass stars, we do not find a significant dependence of disk frequency on stellar mass. These results can help to better constrain theories on gas giant planet formation timescales. Second, in the OrionA molecular cloud, in the mass range of 0.35-0.7M_{sun}_, we provide the most robust evidence to date for disk evolution within a single cluster exhibiting modest age spread. By using surface gravity as an age indicator and employing 4.5{mu}m excess as a primordial disk diagnostic, we observe a trend of decreasing disk frequency for older stars. The detection of intra-cluster disk evolution in NGC1333 and IC348 is tentative, since the slight decrease of disk frequency for older stars is a less than 1{sigma} effect.
- ID:
- ivo://CDS.VizieR/J/ApJ/726/19
- Title:
- Intermediate-mass stars in IC 1805
- Short Name:
- J/ApJ/726/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a study of the intermediate- and high-mass stars in the young, rich star-forming complex IC 1805, based on a combination of optical, near-infrared, and mid-infrared photometry, and classification spectra. These data provide the basis for characterizing the masses and ages for stars more massive than ~2M_{sun}_ and enable a study of the frequency and character of circumstellar disks associated with intermediate- and high-mass stars. Optically thick accretion disks among stars with masses 2<M/M_{sun}_<4 are rare (~2% of members) and absent among more massive stars. A larger fraction (~10%) of stars with masses 2<M/M_{sun}_<4 appear to be surrounded by disks that have evolved from the initial optically thick accretion phase. We identify four classes of such disks. These classes are based on spectral energy distributions (SEDs) of excess emission above photospheric levels: disks that are (1) optically thin based on the magnitude of the observed excess emission from 2 to 24um, (2) optically thin in their inner regions (r<20AU) and optically thick in their outer regions, (3) exhibit empty inner regions (r<10AU) and optically thin emission in their outer regions, and (4) exhibit empty inner regions and optically thick outer regions. We discuss, and assess the merits and liabilities of, proposed explanations for disks exhibiting these SED types and suggest additional observations that would test these proposals.
- ID:
- ivo://CDS.VizieR/J/ApJ/733/113
- Title:
- IRAC observations of IC 1795
- Short Name:
- J/ApJ/733/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep Spitzer/Infrared Array Camera (IRAC) survey of the OB association IC 1795 carried out to investigate the evolution of protoplanetary disks in regions of massive star formation. Combining Spitzer/IRAC data with Chandra/Advanced CCD Imaging Spectrometer observations, we find 289 cluster members. An additional 340 sources with an infrared excess, but without X-ray counterpart, are classified as cluster member candidates. Both surveys are complete down to stellar masses of about 1M_{sun}_. We present pre-main-sequence isochrones computed for the first time in the Spitzer/IRAC colors. The age of the cluster, determined via the location of the Class III sources in the [3.6]-[4.5]/[3.6] color-magnitude diagram, is in the range of 3-5Myr. As theoretically expected, we do not find any systematic variation in the spatial distribution of disks within 0.6pc of either O-type star in the association. However, the disk fraction in IC 1795 does depend on the stellar mass: sources with masses >2M_{sun}_ have a disk fraction of ~20%, while lower mass objects (2-0.8M_{sun}_) have a disk fraction of ~50%. This implies that disks around massive stars have a shorter dissipation timescale.
- ID:
- ivo://CDS.VizieR/J/ApJ/719/9
- Title:
- IRAC point-source catalog of Vela-D cloud
- Short Name:
- J/ApJ/719/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the observations of Cloud D in the Vela Molecular Ridge, obtained with the Infrared Array Camera (IRAC) camera on board the Spitzer Space Telescope at the wavelengths {lambda}=3.6, 4.5, 5.8, and 8.0um. A photometric catalog of point sources, covering a field of approximately 1.2deg^2^, has been extracted and complemented with additional available observational data in the millimeter region. Previous observations of the same region, obtained with the Spitzer MIPS camera in the photometric bands at 24um and 70um, have also been reconsidered to allow an estimate of the spectral slope of the sources in a wider spectral range. A total of 170299 point sources, detected at the 5{sigma} sensitivity level in at least one of the IRAC bands, have been reported in the catalog. There were 8796 sources for which good quality photometry was obtained in all four IRAC bands. For this sample, a preliminary characterization of the young stellar population based on the determination of spectral slope is discussed; combining this with diagnostics in the color-magnitude and color-color diagrams, the relative population of young stellar objects (YSOs) in different evolutionary classes has been estimated and a total of 637 candidate YSOs have been selected.
- ID:
- ivo://CDS.VizieR/J/A+A/659/A67
- Title:
- IRAM spectra of 4 Class I sources
- Short Name:
- J/A+A/659/A67
- Date:
- 14 Mar 2022 07:44:22
- Publisher:
- CDS
- Description:
- Class I protostars are a bridge between Class 0 protostars (<=10^5^yr old), and Class II (>=10^6^yr) protoplanetary disks. Recent studies show gaps and rings in the dust distribution of disks younger than 1Myr, suggesting that planet formation may start already at the Class I stage. To understand what chemistry planets will inherit, it is crucial to characterize the chemistry of Class I sources and o investigate how chemical complexity evolves from Class 0 protostars to protoplanetary disks. There are two goals: (i) to perform a census of the molecular complexity in a sample of four Class I protostars, and (ii) to compare the data with the chemical compositions of earlier and later phases of the Sun-like star formation process. We performed IRAM-30m observations at 1.3mm towards four Class I objects (L1489-IRS, B5-IRS1, L1455-IRS1, and L1551-IRS5). The column densities of the detected species were derived assuming local thermodynamic equilibrium (LTE) or large velocity gradients (LVGs). We detected 27 species: C-chains, N-bearing species, S-bearing species, Si-bearing species, deuterated molecules, and interstellar complex organic molecules (iCOMs; CH_3_OH, CH_3_CN, CH_3_CHO, and HCOOCH_3_). Among the members of the observed sample, L1551-IRS5 is the most chemically rich source. Different spectral profiles are observed: (i) narrow lines (~1km/s) towards all the sources, (ii) broader lines (~4km/s) towards L1551-IRS5, and (iii) line wings due to outflows (in B5-IRS1, L1455-IRS1, and L1551-IRS5). Narrow c-C_3_H_2_ emission originates from the envelope with temperatures of 5-25K and sizes of ~2"-10". The iCOMs in L1551-IRS5 reveal the occurrence of hot corino chemistry, with CH_3_OH and CH_3_CN lines originating from a compact (~0.15") and warm (T>50K) region. Finally, OCS and H_2_S seem to probe the circumbinary disks in the L1455-IRS1 and L1551-IRS5 binary systems. The deuteration in terms of elemental D/H in the molecular envelopes is: ~10-70% (D_2_CO/H_2_CO), ~5-15% (HDCS/H_2_CS), and ~1-23% (CH_2_DOH/CH_3_OH). For the L1551-IRS5 hot corino we derive D/H~2% (CH_2_DOH/CH_3_OH). Carbon chain chemistry in extended envelopes is revealed towards all the sources. In addition, B5-IRS1, L1455-IRS1, and L1551-IRS5 show a low-excitation methanol line that is narrow and centered at systemic velocity, suggesting an origin from an extended structure, plausibly UV-illuminated. The abundance ratios of CH_3_CN, CH_3_CHO, and HCOOCH_3_ with respect to CH_3_OH measured towards the L1551-IRS5 hot corino are comparable to that estimated at earlier stages (prestellar cores, Class 0 protostars), and to that found in comets. The deuteration in our sample is also consistent with the values estimated for sources at earlier stages. These findings support the inheritance scenario from prestellar cores to the Class I phase when planets start forming.
