- ID:
- ivo://CDS.VizieR/J/ApJ/821/52
- Title:
- NIR survey of Spitzer YSOs in Orion Mol. Cloud
- Short Name:
- J/ApJ/821/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a near-infrared survey for the visual multiples in the Orion molecular clouds region at separations between 100 and 1000au. These data were acquired at 1.6um with the NICMOS and WFC3 cameras on the Hubble Space Telescope. Additional photometry was obtained for some of the sources at 2.05um with NICMOS and in the L' band with NSFCAM2 on NASA's InfraRed Telescope Facility. Toward 129 protostars and 197 pre-main-sequence stars with disks observed with WFC3, we detect 21 and 28 candidate companions between the projected separations of 100-1000au, of which less than 5 and 8, respectively, are chance line-of-sight coincidences. The resulting companion fraction (CF) after the correction for the line-of-sight contamination is 14.4_-1.3_^+1.1^ for protostars and 12.5_-0.8_^+1.2^ for the pre-main-sequence stars. These values are similar to those found for main-sequence stars, suggesting that there is little variation in the CF with evolution, although several observational biases may mask a decrease in the CF from protostars to the main-sequence stars. After segregating the sample into two populations based on the surrounding surface density of young stellar objects, we find that the CF in the high stellar density regions ({Sigma}_YSO_>45pc^-2^) is approximately 50% higher than that found in the low stellar density regions ({Sigma}_YSO_<45pc^-2^). We interpret this as evidence for the elevated formation of companions at 100-1000 au in the denser environments of Orion. We discuss possible reasons for this elevated formation.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/644/A29
- Title:
- 14N/15N ratio in YSOs
- Short Name:
- J/A+A/644/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nitrogen isotopic ratio is considered an important diagnostic tool of the star formation process, and N_2_H^+^ is particularly important because it is directly linked to molecular nitrogen N_2_. However, theoretical models still lack to provide an exhaustive explanation for the observed^14^N/^15^N values. Recent theoretical works suggest that the^14^N/^15^N behaviour is dominated by two competing reactions that destroy N_2_H^+^: dissociative recombination and reaction with CO. When CO is depleted from the gas phase, if N_2_H^+^ recombination rate is lower with respect to the N^15^NH^+^ one, the rarer isotopologue is destroyed faster. In prestellar cores, due to a combination of low temperatures and high densities, most CO is frozen in ices onto the dust grains, leading to high levels of depletion. On the contrary, in protostellar cores, where temperature are higher, CO ices evaporate back to the gas phase. This implies that the N_2_H^+^ isotopic ratio in protostellar cores should be lower than the one in prestellar cores, and consistent with the elemental value of ~440. We aim to test this hypothesis, producing the first sample of N_2_H^+^ /N^15^NH^+^ measurements in low mass protostars. We observe the N_2_H^+^ and N^15^NH^+^ lowest rotational transition towards six young stellar objects in Perseus and Taurusmolecular clouds. We model the spectra with a custom python code using a constant T_ex_ approach to fit the observations. We discuss in appendix the validity of this hypothesis. The derived column densities are used to compute the nitrogen isotopic ratios. Our analysis yields an average of^14^N/^15^N|_pro_=420+/-15 in the protostellar sample. This is consistent with the protosolar value of 440, and significantly lower than the average value previously obtained in a sample of prestellar objects. Our results are in agreement with the hypothesis that, when CO is depleted from the gas-phase, dissociative recombinations with free electrons destroy N^15^NH^+^ faster than N_2_H^+^ , leading to high isotopic ratios in prestellar cores, where carbon monoxide is frozen onto dust grains.
- ID:
- ivo://CDS.VizieR/J/ApJ/707/103
- Title:
- Observation of Ser FIRS 1 at 230GHz
- Short Name:
- J/ApJ/707/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results of a program to characterize the disk and envelope structure of typical Class 0 protostars in nearby low-mass star-forming regions. We use Spitzer Infrared Spectrograph (IRS) mid-infrared spectra, high-resolution Combined Array for Research in Millimeter-wave Astronomy (CARMA) 230GHz continuum imaging, and two-dimensional radiative transfer models to constrain the envelope structure, as well as the size and mass of the circumprotostellar disk in Serpens FIRS 1. The primary envelope parameters (centrifugal radius, outer radius, outflow opening angle, and inclination) are well constrained by the spectral energy distribution (SED), including Spitzer IRAC and MIPS photometry, IRS spectra, and 1.1mm Bolocam photometry. These together with the excellent uv-coverage (4.5-500k{lambda}) of multiple antenna configurations with CARMA allow for a robust separation of the envelope and a resolved disk. The SED of Serpens FIRS 1 is best fit by an envelope with the density profile of a rotating, collapsing spheroid with an inner (centrifugal) radius of approximately 600AU, and the millimeter data by a large resolved disk with M_disk_~1.0M_{sun}_ and R_disk_~300AU.
- ID:
- ivo://CDS.VizieR/J/A+A/596/A26
- Title:
- OMC-2 FIR 3 and FIR 4 [OI] maps
- Short Name:
- J/A+A/596/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first detection of a jet in the far-IR [OI] lines from an intermediate mass protostar. We have carried out a Herschel/PACS spectral mapping study in the [OI] lines of OMC-2 FIR 3 and FIR 4, two of the most luminous protostars in Orion outside of the Orion Nebula. The spatial morphology of the fine structure line emission reveals the presence of an extended photodissociation region (PDR) and a narrow, but intense jet emission connecting the two protostars. The jet seen in [OI] emission is spatially aligned with the Spitzer/IRAC 4.5um jet and the CO (6-5) molecular outflow centered on FIR 3. The mass loss rate derived from the total [OI] 63um line luminosity of the jet is 7.7*10^-6^M_{sun}_/yr, which is more than an order of magnitude higher than that measured for typical low mass class 0 protostars. The implied accretion luminosity is significantly higher than the observed bolometric luminosity of FIR 4, indicating that the [OI] jet is unlikely to be associated with FIR 4. We argue that the peak line emission seen toward FIR 4 originates in the terminal shock produced by the jet driven by FIR 3. The higher mass loss rate that we find for FIR 3 is consistent with the idea that intermediate mass protostars drive more powerful jets than their low-mass counterparts. Our results also call into question the nature of FIR 4.
295. Oph A mosaic image
- ID:
- ivo://CDS.VizieR/J/A+A/631/A58
- Title:
- Oph A mosaic image
- Short Name:
- J/A+A/631/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity, which are intimately connected to the evolution of protoplanetary disks and the formation of planets. We have carried out sensitive continuum observations toward the Ophiuchus A star-forming region using the Karl G. Jansky Very Large Array (VLA) at 10GHz over a field-of-view of 6' with a spatial resolution of {theta}_maj_x{theta}_min_~0.4"x0.2". We achieved a 5{mu}Jy/beam root-mean-square noise level at the center of our mosaic field of view. Among the eighteen sources we detected, sixteen are YSOs (three Class 0, five Class I, six Class II, and two Class III) and two are extragalactic candidates.We find that thermal dust emission generally contributes less that 30% of the emission at 10GHz. The radio emission is dominated by other types of emission such as gyro-synchrotron radiation from active magnetospheres, free-free emission from thermal jets, free-free emission from the outflowing photo-evaporated disk material, and/or synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections towards Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain the disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve with time. The sensitivity of our data cannot exclude photoevaporation due to X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys with the Square Kilometre Array will be able to provide strong constraints on disk photoevaporation.
- ID:
- ivo://CDS.VizieR/J/AJ/159/153
- Title:
- Optical and IR photometry in the HII region Sh2-242
- Short Name:
- J/AJ/159/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here identification and characterization of the young stellar population associated with an active star-forming site Sh2-242. We used our own new optical imaging and spectroscopic observational data, as well as several archival catalogs, e.g., Pan-STARRS-1, Gaia-DR2, Isaac Newton Telescope Photometric H-Alpha Survey (IPHAS), Wide-field InfraRed Camera, 2MASS, and Spitzer. Slit spectroscopic results confirm the classification of the main ionizing source BD+26980 as an early-type star of spectral type B0.5V. The spectrophotometric distance of the star is estimated as 2.08{+/-}0.24kpc, which confirms the source as a member of the cluster. An extinction map covering a large area (diameter ~50') is generated with H and K photometry toward the region. From the map, three distinct locations of peak extinction complexes (A_V_~7-17mag) are identified for the very first time. Using the infrared color excess, a total of 33 Class I and 137 Class II young objects are classified within the region. The IPHAS photometry reveals classification of 36 H{alpha} emitting sources, which might be class II objects. Among 36 H{alpha} emitting sources, 5 are already identified using infrared excess emission. In total, 201 young objects are classified toward S242 from this study. The membership status of the young sources is further windowed with the inclusion of parallax from the Gaia DR2 catalog. Using the optical and infrared color-magnitude diagrams, the young stellar objects are characterized with an average age of ~1Myr and masses in the range 0.1-3.0M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/1542
- Title:
- Optical high-resolution spectroscopy of WTTSs
- Short Name:
- J/ApJ/723/1542
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution spectroscopic observations for a sample of 19 weak-line T Tauri stars (WTTSs). Based on these observations and data of 108 WTTSs taken from the literature, we derive lithium abundances for 127 WTTSs. Investigation of a possible relation between lithium and rotation in WTTSs shows that: (1) rapidly rotating WTTSs have comparatively lower lithium abundances than their slower rotating counterparts; (2) in the spectral-type range G0-K0, most of the WTTSs share the same Li content irrespective of their Teff; and (3) active late-type binaries do not obey the correlation between lithium abundances and rotation periods, since the tidally locked rotation of the late-type binary system leads naturally to slower lithium destruction rates.
- ID:
- ivo://CDS.VizieR/J/ApJ/664/481
- Title:
- Optical/IR photometry of Collinder 69
- Short Name:
- J/ApJ/664/481
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present multiwavelength optical and IR photometry of 170 previously known low-mass stars and brown dwarfs of the 5Myr Collinder 69 cluster ({lambda} Orionis). The new photometry supports cluster membership for most of them, with less than 15% of the previous candidates identified as probable nonmembers. The near-IR photometry allows us to identify stars with IR excesses, and we find that the Class II population is very large, around 25% for stars (in the spectral range M0-M6.5) and 40% for brown dwarfs, down to 0.04M_{sun}_, despite the fact that the H{alpha} equivalent width is low for a significant fraction of them. In addition, there are a number of substellar objects, classified as Class III, that have optically thin disks. The Class II members are distributed in an inhomogeneous way, lying preferentially in a filament running toward the southeast. The IR excesses for the Collinder 69 members range from pure Class II (flat or nearly flat spectra longward of 1um), to transition disks with no near-IR excess but excesses beginning within the IRAC wavelength range, to two stars with excess only detected at 24um. Collinder 69 thus appears to be at an age where it provides a natural laboratory for the study of primordial disks and their dissipation.
- ID:
- ivo://CDS.VizieR/J/ApJ/720/679
- Title:
- Optical spectroscopy in Cygnus X region
- Short Name:
- J/ApJ/720/679
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new images and photometry of the massive star-forming complex Cygnus X obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. A combination of IRAC, MIPS, UKIRT Deep Infrared Sky Survey, and Two Micron All Sky Survey data are used to identify and classify young stellar objects (YSOs). Of the 8231 sources detected exhibiting infrared excess in Cygnus X North, 670 are classified as class I and 7249 are classified as class II. Using spectra from the FAST Spectrograph at the Fred L. Whipple Observatory and Hectospec on the MMT, we spectrally typed 536 sources in the Cygnus X complex to identify the massive stars. We find that YSOs tend to be grouped in the neighborhoods of massive B stars (spectral types B0 to B9).
- ID:
- ivo://CDS.VizieR/J/ApJ/844/138
- Title:
- Optical spectroscopy toward Orion B fields
- Short Name:
- J/ApJ/844/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from high-resolution optical spectra toward 66 young stars in the Orion B molecular cloud to study their kinematics and other properties. Observations of the H{alpha} and Li I 6707{AA} lines are used to check membership and accretion properties. While the stellar radial velocities of NGC 2068 and L1622 are in good agreement with that of the molecular gas, many of the stars in NGC 2024 show a considerable offset. This could be a signature of either the expansion of the cluster, the high degree of the ejection of the stars from the cluster through dynamical interaction, or the acceleration of the gas due to stellar feedback.
