- ID:
- ivo://CDS.VizieR/J/ApJ/845/87
- Title:
- CGS. V. Statistical study of bars and buckled bars
- Short Name:
- J/ApJ/845/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle (i), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high i) or as a barlens structure (at low i). We visually identify bars, boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and buckled bar fractions on host galaxy properties, including Hubble type, stellar mass, color, and gas mass fraction. We find that the barred and unbarred disks show similar distributions in these physical parameters. The bar fraction is higher (70%-80%) in late-type disks with low stellar mass (M*<10^10.5^M_{sun}_) and high gas mass ratio. In contrast, the buckled bar fraction increases to 80% toward massive and early-type disks (M*>10^10.5^M_{sun}_), and decreases with higher gas mass ratio. These results suggest that bars are more difficult to grow in massive disks that are dynamically hotter than low-mass disks. However, once a bar forms, it can easily buckle in the massive disks, where a deeper potential can sustain the vertical resonant orbits. We also find a probable buckling bar candidate (ESO506-G004) that could provide further clues to understand the timescale of the buckling process.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/646/A46
- Title:
- Chamaeleon DANCe. Stellar population with Gaia-DR2
- Short Name:
- J/A+A/646/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kinematic properties and stellar parameters of the Chamaeleon stars selected in our membership analysis using Gaia-DR2 data. We provide for each star its identifier, position, proper motion, parallax, radial velocity, distance, spatial velocity, SED classification, age and membership probability. We also provide the membership probabilities for all sources in the fields surveyed by our study and the empirical isochrone of the Cha I and Cha II subgroups.
- ID:
- ivo://CDS.VizieR/J/A+A/535/A2
- Title:
- Chamaeleon III 870um sources maps
- Short Name:
- J/A+A/535/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nearby Chamaeleon molecular cloud complex is a good laboratory for studying the process of low-mass star formation because it consists of three clouds with very different properties. Chamaeleon III does not show any sign of star formation, while star formation has been very active in Chamaeleon I and may already be finishing. Our goal is to determine whether star formation can proceed in Cha III by searching for prestellar cores, and to compare the results to our recent survey of Cha I.
- ID:
- ivo://CDS.VizieR/J/ApJ/602/816
- Title:
- Chamaeleon I star-forming region census
- Short Name:
- J/ApJ/602/816
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present a new census of the members of the Chamaeleon I star-forming region. Optical spectroscopy has been obtained for 179 objects that have been previously identified as possible members of the cluster, that lack either accurate spectral types or clear evidence of membership, and that are optically visible (I<~18). I have used these spectroscopic data and all other available constraints to evaluate the spectral classifications and membership status of a total sample of 288 candidate members of Chamaeleon I that have appeared in published studies of the cluster. The latest census of Chamaeleon I now contains 158 members, eight of which are later than M6 and thus are likely to be brown dwarfs. I find that many of the objects identified as members of Chamaeleon I in recent surveys are actually field stars. Meanwhile, seven of nine candidates discovered by Carpenter and coworkers are confirmed as members, one of which is the coolest known member of Chamaeleon I at a spectral type of M8 (~0.03M_{sun}_). I have estimated extinctions, luminosities, and effective temperatures for the members and used these data to construct an H-R diagram for the cluster. Chamaeleon I has a median age of ~2Myr according to evolutionary models and hence is similar in age to IC 348 and is slightly older than Taurus (~1Myr). The measurement of an initial mass function for Chamaeleon I from this census is not possible because of the disparate methods with which the known members were originally selected and must await an unbiased, magnitude-limited survey of the cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A145
- Title:
- Chamaeleon I 870um sources
- Short Name:
- J/A+A/527/A145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chamaeleon I is the most active region in terms of star formation in the Chamaeleon molecular cloud complex. Although it is one of the nearest low-mass star forming regions, its population of prestellar and protostellar cores is not known and a controversy exists concerning its history of star formation. Our goal is to search for prestellar and protostellar cores and characterize the earliest stages of star formation in this cloud.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A99
- Title:
- Chamaeleon-MMS1 NH_3_ (1,1) and (2,2) maps
- Short Name:
- J/A+A/564/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this study is to investigate the structure and kinematics of the nearby candidate first hydrostatic core Cha-MMS1. Cha-MMS1 was mapped in the NH_3_(1,1) line and the 1.2cm continuum using the Australia Telescope Compact Array, ATCA. The angular resolution of the ATCA observations is 7" (~1000AU), and the velocity resolution is 50m/s. The core was also mapped with the 64-m Parkes telescope in the NH_3_(1,1) and (2,2) lines. Observations from Herschel Space Observatory and Spitzer Space telescope were used to help interpretation. The ammonia spectra were analysed using Gaussian fits to the hyperfine structure. A two-layer model was applied in the central parts of the core where the ATCA spectra show signs of self-absorption.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A126
- Title:
- Cha-MMS1 CO 3-2 and ^13^CO 3-2 datacubes
- Short Name:
- J/A+A/633/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of its low luminosity, its chemical composition, and the absence of a large-scale outflow, the dense core Cha-MMS1 located in the Chamaeleon I molecular cloud was proposed as a first hydrostatic core (FHSC) candidate a decade ago. Our goal is to test this hypothesis by searching for a slow, compact outflow driven by Cha-MMS1 that would match the predictions of MHD simulations for this short phase of star formation. We use the Atacama Large Millimeter/submillimeter Array (ALMA) to map Cha-MMS1 at high angular resolution in CO 3-2 and ^13^CO 3-2 as well as in continuum emission. We report the detection of a bipolar outflow emanating from the central core, along a (projected) direction roughly parallel to the filament in which Cha-MMS1 is embedded and perpendicular to the large-scale magnetic field. The morphology of the outflow indicates that its axis lies close to the plane of the sky. We measure velocities corrected for inclination of more than 90km/s which is clearly incompatible with the expected properties of a FHSC outflow. Several properties of the outflow are determined and compared to previous studies of Class 0 and Class I protostars. The outflow of Cha-MMS1 has a much smaller momentum force than the outflows of other Class0 protostars. In addition, we find a dynamical age of 200-3000yr indicating that Cha-MMS1 might be one of the youngest ever observed Class 0 protostars. While the existence of the outflow suggests the presence of a disk, no disk is detected in continuum emission and we derive an upper limit of 55au to its radius. We conclude that Cha-MMS1 has already gone through the FHSC phase and is a young Class 0 protostar, but it has not brought its outflow to full power yet.
- ID:
- ivo://CDS.VizieR/J/ApJS/178/339
- Title:
- ChaMP extended stellar survey (ChESS)
- Short Name:
- J/ApJS/178/339
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 348 X-ray-emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a wide-area serendipitous survey based on archival X-ray images, with the Sloan Digital Sky Survey (SDSS-DR6). We use morphological star/galaxy separation, matching to an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data-quality tests to create our catalog, the ChaMP Extended Stellar Survey (ChESS), from a sample of 2121 matched ChaMP/SDSS sources. Our cuts retain 92% of the spectroscopically confirmed stars in the original sample while excluding 99.6% of the 684 spectroscopically confirmed extragalactic sources. Fewer than 3% of the sources in our final catalog are previously identified stellar X-ray emitters. For 42 catalog members, spectroscopic classifications are available in the literature. We present new spectral classifications and H{alpha} measurements for an additional 79 stars. The catalog is dominated by main-sequence stars; we estimate the fraction of giants in ChESS is ~10%. We identify seven giant stars (including a possible Cepheid and an RR Lyrae star) as ChaMP sources, as well as three cataclysmic variables. Future papers will present analyses of source variability and comparisons of this catalog to models of stellar activity in the Galactic disk.
- ID:
- ivo://CDS.VizieR/J/ApJS/150/19
- Title:
- ChaMP. I. First X-ray source catalog
- Short Name:
- J/ApJS/150/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Chandra Multiwavelength Project (ChaMP) is a wide-area (~14deg^2^) survey of serendipitous Chandra X-ray sources, aiming to establish fair statistical samples covering a wide range of characteristics (such as absorbed active galactic nuclei, high-z clusters of galaxies) at flux levels (fX~10^-15^ to 10^-14^erg/s/cm^2^) ) intermediate between the Chandra deep surveys and previous missions. We present the first ChaMP catalog, which consists of 991 near on-axis, bright X-ray sources obtained from the initial sample of 62 observations. The data have been uniformly reduced and analyzed with techniques specifically developed for the ChaMP and then validated by visual examination. To assess source reliability and positional uncertainty, we perform a series of simulations and also use Chandra data to complement the simulation study. The false source detection rate is found to be as good as or better than expected for a given limiting threshold. On the other hand, the chance of missing a real source is rather complex, depending on the source counts, off-axis distance (or PSF), and background rate. The positional error (95% confidence level) is usually less than 1" for a bright source, regardless of its off-axis distance, while it can be as large as 4" for a weak source (~20counts) at a large off-axis distance (Doff-axis>8'). We have also developed new methods to find spatially extended or temporary variable sources, and those sources are listed in the catalog.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/1702
- Title:
- ChaMPlane deep galactic bulge survey. I.
- Short Name:
- J/ApJ/700/1702
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a deep X-ray and optical survey with Chandra and HST of low-extinction regions in the Galactic bulge. Here we present the results of a search for low-luminosity (L_X_<~10^34^erg/s) accreting binaries among the Chandra sources in the region closest to the Galactic center, at an angular offset of 1.4{deg}, that we have named the Limiting Window (LW). Based on their blue optical colors, excess H{alpha} fluxes, and high X-ray-to-optical flux ratios, we identify three likely accreting binaries; these are probably white dwarfs accreting from low-mass companions (cataclysmic variables; CVs) although we cannot exclude that they are quiescent neutron-star or black-hole low-mass X-ray binaries. Distance estimates put these systems farther than >~2kpc. Based on their H{alpha}-excess fluxes and/or high X-ray-to-optical flux ratios, we find 22 candidate accreting binaries; however, the properties of some can also be explained if they are dMe stars or active galaxies.