Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/618/A110
- Title:
- IR nebulae around bright massive stars
- Short Name:
- J/A+A/618/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies show that more than 70% of massive stars do not evolve as effectively single stars, but as members of interacting binary systems. The evolution of these stars is thus strongly altered compared to similar but isolated objects. We investigate the occurrence of parsec-scale mid-infrared nebulae around early-type stars. If they exist over a wide range of stellar properties, one possible overarching explanation is non-conservative mass transfer in binary interactions, or stellar mergers. For ~3850 stars (all OBA stars in the Bright Star Catalogue (BSC, Cat. V/50), Be stars, BeXRBs, and Be+sdO systems), we visually inspect WISE 22um images. Based on nebular shape and relative position, we distinguish five categories: offset bow shocks structurally aligned with the stellar space velocity, unaligned offset bow shocks, and centered, unresolved, and not classified nebulae. In the BSC, we find that 28%, 13%, and 0.4% of all O, B, and A stars, respectively, possess associated infrared (IR) nebulae. Additionally, 34/234 Be stars, 4/72 BeXRBs, and 3/17 Be+sdO systems are associated with IR nebulae. Aligned or unaligned bow shocks result from high relative velocities between star and interstellar medium (ISM) that are dominated by the star or the ISM, respectively. About 13% of the centered nebulae could be bow shocks seen head- or tail-on. For the rest, the data disfavor explanations as remains of parental disks, supernova remnants of a previous companion, and dust production in stellar winds. The existence of centered nebulae also at high Galactic latitudes strongly limits the global risk of coincidental alignments with condensations in the ISM. Mass loss during binary evolution seems a viable mechanism for the formation of at least some of these nebulae. In total, about 29% of the IR nebulae (2% of all OBA stars in the BSC) may find their explanation in the context of binary evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A26
- Title:
- Molecular ion abundances in diffuse ISM
- Short Name:
- J/A+A/622/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The transition between atomic and molecular hydrogen is associated with important changes in the structure of interstellar clouds, and marks the beginning of interstellar chemistry. Most molecular ions are rapidly formed (in ion-molecule reactions) and destroyed (by dissociative recombination) in the diffuse ISM. Because of the relatively simple networks controlling their abundances, molecular ions are usually good probes of the underlying physical conditions including for instance the fraction of gas in molecular form or the fractional ionization. In this paper we focus on three possible probes of the molecular hydrogen column density, HCO^+^, HOC^+^, and CF^+^. We presented high sensitivity ALMA absorption data toward a sample of compact HII regions and bright QSOs with prominent foreground absorption, in the ground state transitions of the molecular ions HCO^+^, HOC^+^, and CF^+^ and the neutral species HCN and HNC, and from the excited state transitions of C_3_H^+^(4-3) and ^13^CS(2-1). These data are compared with Herschel absorption spectra of the ground state transition of HF and p-H_2_O. We show that the HCO^+^, HOC^+^, and CF^+^ column densities are well correlated with each other. HCO^+^ and HOC^+^ are tightly correlated with p-H_2_O, while they exhibit a different correlation pattern with HF depending on whether the absorbing matter is located in the Galactic disk or in the central molecular zone. We report new detections of C_3_H^+^ confirming that this ion is ubiquitous in the diffuse matter, with an abundance relative to H_2_ of ~7x10^-11^. We confirm that the CF^+^ abundance is lower than predicted by simple chemical models and propose that the rate of the main formation reaction is lower by a factor of about 3 than usually assumed. In the absence of CH or HF data, we recommend to use the ground state transitions of HCO^+^, CCH, and HOC^+^ to trace diffuse molecular hydrogen, with mean abundances relative to H_2_ of 3x10^-9^, 4x10^-8^ and 4x10^-11^ respectively, leading to sensitivity N(H_2_)/{int}{tau}dv of 4x10^20^, 1.5x10^21^, and 6x10^22^cm^-2^/km/s, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A8
- Title:
- MUSE Hubble Ultra Deep Field Survey. VIII
- Short Name:
- J/A+A/608/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the detection of 145 extended Lyman-alpha haloes around individual high-z (3-6) star-forming galaxies in the UDF field observed by MUSE/VLT. Using a 2D, two-component (continuum-like and halo) decomposition of Lyman-alpha emission assuming circular exponential distributions, we measure scale lengths and luminosities of Lyman-alpha haloes.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A172
- Title:
- Photoionization of the CH radical
- Short Name:
- J/A+A/654/A172
- Date:
- 07 Mar 2022 07:12:57
- Publisher:
- CDS
- Description:
- The primary motivation of this paper is to provide accurate data for the photoionization of the CH radical, including absolute total photoionization cross section, partial cross sections and photo electron angular distribution. In addition,the near threshold features in the photoionization curve (which are absent in previous studies) are produced with high precision. A multichannel wavefunction based on R-matrix approach, which uses the configuration interaction (CI) method to describe electronic correlation, is carried out in the present calculations. A set of B-spline orbitals is employed to represent the accurate continuum. The distinctive feature of the present calculations allows us to generate a more accurate description of the bound and continuum states than those employed before. Total photoionization cross sections from the ground state of CH radicals and partial cross sections corresponding to 1{pi}, 3{sigma}, and 2{sigma} states of CH+ ions are presented for photon energies ranging from threshold to 80eV. Extensive resonance structures, which are absent in previous studies, near the ionization threshold, are observed for the first time. The cross-section dataset obtained from the present calculations is expected to be sufficiently accurate and comprehensive for most current modeling applications involving the photon and CH radicals scattering system.
- ID:
- ivo://CDS.VizieR/J/ApJS/185/451
- Title:
- PMS stars in the Cepheus flare region
- Short Name:
- J/ApJS/185/451
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of optical spectroscopic and BVR_C_I_C_ photometric observations of 77 pre-main-sequence (PMS) stars in the Cepheus flare region. A total of 64 of these are newly confirmed PMS stars, originally selected from various published candidate lists. We estimate effective temperatures and luminosities for the PMS stars, and comparing the results with PMS evolutionary models, we estimate stellar masses of 0.2-2.4M_{sun}_ and stellar ages of 0.1-15Myr. Among the PMS stars, we identify 15 visual binaries with separations of 2-10". From archival IRAS, Two Micron All Sky Survey, and Spitzer data, we construct their spectral energy distributions (SEDs) and classify 5% of the stars as Class I, 10% as Flat SED, 60% as Class II, and 3% as Class III young stellar objects. We identify 12 classical T Tauri stars and two weak-line T Tauri stars as members of NGC 7023, with a mean age of 1.6Myr. The 13 PMS stars associated with L1228 belong to three small aggregates: RNO 129, L1228A, and L1228S. The age distribution of the 17 PMS stars associated with L1251 suggests that star formation has propagated with the expansion of the Cepheus flare shell. We detect sparse aggregates of ~6-7Myr old PMS stars around the dark clouds L1177 and L1219, at a distance of ~400pc. Three T Tauri stars appear to be associated with the Herbig Ae star SV Cep at a distance of 600pc. Our results confirm that the molecular complex in the Cepheus flare region contains clouds of various distances and star-forming histories.
- ID:
- ivo://CDS.VizieR/J/ApJ/728/70
- Title:
- The abundance of boron in diffuse clouds
- Short Name:
- J/ApJ/728/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive survey of boron abundances in diffuse interstellar clouds from observations made with the Space Telescope Imaging Spectrograph (STIS) of the Hubble Space Telescope. Our sample of 56 Galactic sight lines is the result of a complete search of archival STIS data for the BII{lambda}1362 resonance line, with each detection confirmed by the presence of absorption from OI{lambda}1355, CuII{lambda}1358, and GaII{lambda}1414 (when available) at the same velocity. Five previous measurements of interstellar BII from Goddard High Resolution Spectrograph (GHRS) observations are incorporated in our analysis, yielding a combined sample that more than quadruples the number of sight lines with significant boron detections. Our survey also constitutes the first extensive analysis of interstellar gallium from STIS spectra and expands on previously published results for oxygen and copper. The observations probe both high- and low-density diffuse environments, allowing the density-dependent effects of interstellar depletion to be clearly identified in the gas-phase abundance data for each element.
- ID:
- ivo://CDS.VizieR/J/ApJS/185/198
- Title:
- The Cepheus flare observed with IRAC and MIPS
- Short Name:
- J/ApJS/185/198
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer Infrared Array Camera (IRAC; ~2deg^2^) and Multiband Imaging Photometer for Spitzer (MIPS; ~8deg^2^) observations of the Cepheus Flare, which is associated with the Gould Belt, at an approximate distance of ~300pc. Around 6500 sources are detected in all four IRAC bands, of which ~900 have MIPS 24um detections. We identify 133 young stellar object (YSO) candidates using color-magnitude diagram techniques, and a large number of the YSO candidates are associated with the NGC 7023 reflection nebula. Cross-identifications were made with the Guide Star Catalog II and the IRAS Faint Source Catalog, and spectral energy distributions (SEDs) were constructed. SED modeling was conducted to estimate the degree of infrared excess. It was found that a large majority of disks were optically thick accreting disks, suggesting that there has been little disk evolution in these sources. Nearest-neighbor clustering analysis identified four small protostellar groups (L1228, L1228N, L1251A, and L1251B) with 5-15 members each and the larger NGC 7023 association with 32 YSO members. The star-formation efficiency for cores with clusters of protostars and for those without clusters was found to be ~8% and ~1%, respectively. The cores L1155, L1241, and L1247 are confirmed to be starless down to our luminosity limit of L_bol_=0.06L_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/758/44
- Title:
- The GALFA-HI compact cloud catalog
- Short Name:
- J/ApJ/758/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 1964 isolated, compact neutral hydrogen clouds from the Galactic Arecibo L-Band Feed Array Survey Data Release One. The clouds were identified by a custom machine-vision algorithm utilizing the difference of Gaussian kernels to search for clouds smaller than 20'. The clouds have velocities typically between |V_LSR_|=20 and 400km/s, line widths of 2.5-35km/s, and column densities ranging from 1 to 35x10^18^/cm2. The distances to the clouds in this catalog may cover several orders of magnitude, so the masses may range from less than a solar mass for clouds within the Galactic disk, to greater than 10^4^M_{sun}_for high-velocity clouds (HVCs) at the tip of the Magellanic Stream. To search for trends, we separate the catalog into five populations based on position, velocity, and line width: HVCs; galaxy candidates; cold low-velocity clouds (LVCs); warm, low positive-velocity clouds in the third Galactic quadrant; and the remaining warm LVCs. The observed HVCs are found to be associated with previously identified HVC complexes. We do not observe a large population of isolated clouds at high velocities as some models predict. We see evidence for distinct histories at low velocities in detecting populations of clouds corotating with the Galactic disk and a set of clouds that is not corotating.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/77
- Title:
- Ultra-compact high velocity clouds from ALFALFA
- Short Name:
- J/ApJ/768/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34Jy.km/s, median angular diameters of 10', and median velocity widths of 23km/s. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of ~1Mpc, the UCHVCs have neutral hydrogen (HI) masses of ~10^5^-10^6^M_{sun}_, HI diameters of ~2-3kpc, and indicative dynamical masses within the HI extent of ~10^7^-10^8^M_{sun}_, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.
- « Previous
- Next »
- 1
- 2
- 3
