- ID:
- ivo://CDS.VizieR/J/ApJ/878/21
- Title:
- Vertical motions of APOGEE & Gaia red clump stars
- Short Name:
- J/ApJ/878/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has long been known that the vertical motions of Galactic disk stars increase with stellar age, commonly interpreted as vertical heating through orbit scattering. Here we map the vertical actions of disk stars as a function of age ({tau}<=8Gyr) and across a large range of Galactocentric radii, R_GC_, drawing on APOGEE and Gaia data. We fit J_z_(R_GC,{tau}_) as a combination of the vertical action at birth, J_z,0_, and the subsequent heating {Delta}J_z,1Gyr_(R_GC_), which scales as {tau}^{gamma}(R_GC_)^. The inferred birth temperature, J_z,0_(R_GC_) is 1kpc.km/s for 3kpc<R_GC_<10kpc, consistent with the ISM velocity dispersion, but it rapidly rises outward, to 8kpc.km/s for R_GC_=14kpc, likely reflecting the stars' birth in a warped or flared gas disk. We find the heating rate {Delta}J_z,1Gyr_ to be modest and nearly constant across all radii, 1.6kpc.km/s/Gyr. The stellar age dependence {gamma} gently grows with Galactocentric radius, from {gamma}~1 for R_GC_<~R_{sun}_ to {gamma}~1.3 at R_GC_=14kpc. The observed J_z_-{tau} relation at all radii is considerably steeper ({gamma}>~1) than the time dependence theoretically expected from orbit scattering, J_z_{propto}t^0.5^. We illustrate how this conundrum can be resolved if we also account for the fact that at earlier epochs, the scatterers were more common, and the restoring force from the stellar disk surface mass density was low. Our analysis may reinstate gradual orbital scattering as a plausible and viable mechanism to explain the age-dependent vertical motions of disk stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/853/114
- Title:
- Vertical population gradients in NGC 891. I.
- Short Name:
- J/ApJ/853/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured vertical and radial stellar population gradients in NGC 891. We compare these gradients to those known for the Milky Way from studies of resolved stars. Optical spectroscopic measurements extend spatially from the disk midplane up to 2.6kpc in height and out to a radius of 12kpc on both sides of the galaxy. Data were acquired with {nabla}Pak, a variable-pitch fiber integral field unit (IFU) on the WIYN telescope. We describe the laboratory and on-sky performance of {nabla}Pak, as well as modifications to the standard observational and analysis procedures necessary to calibrate data taken with this unique IFU. {nabla}Pak has a mean throughput of 80% at 5500{AA}. To achieve an estimated precision of 10% in light-weighted mean age and metallicity, we define a set of spatial apertures in radius and height in which spectra are binned to achieve a signal-to-noise ratio of ~20{AA}^-1^. We use spectral indices to measure age, metallicity, and abundance, indicating that NGC 891's stellar populations have 0.2<Z/Z_{sun}_<1 and +0.2dex {alpha}-enhancement on average. We find a clear transition from young (<3-5Gyr) to old (>7Gyr) stellar populations at 0.4kpc, roughly the scale height of the thin disk. We also find a slight trend toward younger populations at larger radii, consistent with flaring in an inside-out disk formation scenario. The vertical age gradient in NGC 891 is in remarkable qualitative agreement with a model for disk heating tuned to studies of the Milk Way's solar cylinder.
- ID:
- ivo://CDS.VizieR/J/A+A/389/795
- Title:
- Vertical structure of edge-on galaxies
- Short Name:
- J/A+A/389/795
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To analyze the vertical structure of edge-on galaxies, we have used images of a large uniform sample of flat galaxies that have been taken during the 2MASS all-sky survey. The photometric parameters, such as the radial scale length, the vertical scale height, and the deprojected central surface brightness of galactic disks have been obtained. We find a strong correlation between the central surface brightness and the ratio of the vertical scale height to the vertical scale length: the thinner the galaxy, the lower the central surface brightness of its disk. The vertical scale height does not increase systematically with the distance from the galaxy center in the frames of this sample.
- ID:
- ivo://CDS.VizieR/J/A+A/267/515
- Title:
- Very cold C-rich circumstellar envelopes
- Short Name:
- J/A+A/267/515
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper develops a method for identification of very cold C-rich circumstellar envelopes (CSEs) in IR regions colder than region VII (i.e., larger value of IRAS flux ratio S25/S12), by reviewing the different criteria and by identifying C-rich CSEs in a sample of 228 bright IRAS sources. By using the results of OH surveys and catalogs together with the results of additional HCN/CO millimeter observations performed on critical classes of objects, a C/O classification is proposed for 94 percent of the sources with a good probability. It is shown that the low-resolution spectra by themselves are a reasonable and easy way to identify C-rich late AGB CSEs. For post-AGB object with cold CSEs, HCN and OH observations or visible/near IR spectroscopy are necessary.
- ID:
- ivo://CDS.VizieR/J/ApJS/225/26
- Title:
- Very Low-Luminosity Objects (VeLLOs) from 1.25-850um
- Short Name:
- J/ApJS/225/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for Very Low-Luminosity Objects (VeLLOs) in the Gould Belt (GB) clouds using infrared and sub-millimeter (sub-mm) data from 1.25 to 850{mu}m and our N_2_H^+^(J=1-0) observations. We modified the criteria by Dunham et al. (2008, J/ApJS/179/249) to select the VeLLOs in the GB clouds, finding 95 VeLLO candidates, 79 of which are newly identified in this study. Out of 95 sources, 44 were detected in both sub-mm continuum and N_2_H^+^ emission and were classified as Group A (the VeLLOs), and 51 sources detected in either sub-mm emission or N_2_H^+^ emission were classified with Group B as candidate VeLLOs. We find that these VeLLOs and the candidates are forming in environments different from those of the likely VeLLOs. Seventy-eight sources are embedded within their molecular clouds, and thus are likely VeLLOs forming in a dense environment. The remaining 17 sources are located in low-level extinction regions (A_V_<1) connected to the clouds, and can be either background sources or candidate substellar objects forming in an isolated mode. The VeLLOs and the candidates are likely more luminous and their envelopes tend to be more massive in denser environments. The VeLLOs and the candidates are more populous in the clouds where more YSOs form, indicating that they form in a manner similar to that of normal YSOs. The bolometric luminosities and temperatures of the VeLLOs are compared to predictions of episodic accretion models, showing that the low luminosities for most VeLLOs can be well explained by their status in the quiescent phases of a cycle of episodic mass accretion.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/176
- Title:
- Very low-mass binaries with Gaia DR2 data
- Short Name:
- J/ApJ/889/176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of WISE 2150-7520AB (W2150AB): a widely separated (~341au) very low-mass L1+T8 co-moving system. The system consists of the previously known L1 primary 2MASS J21501592-7520367 and a newly discovered T8 secondary found at position 21:50:18.99-75:20:54.6 (MJD=57947) using Wide-field Infrared Survey Explorer data via the Backyard Worlds: Planet 9 citizen science project. We present Spitzer ch1 and ch2 photometry (ch1-ch2=1.41+/-0.04mag) of the secondary and Folded-port InfraRed Echellette prism spectra of both components. The sources show no peculiar spectral or photometric signatures, indicating that each component is likely field age. Using all observed data and the Gaia DR2 parallax of 41.3593+/-0.2799mas for W2150A we deduce fundamental parameters of log(L_bol_/L_{sun}_)=-3.69+/-0.01, Teff=2118+/-62K, and an estimated mass=72+/-12M_Jup_ for the L1 and log(L_bol_/L_{sun}_)=-5.64+/-0.02, Teff=719+/-61K, and an estimated mass=34+/-22M_Jup_ for the T8. At a physical separation of ~341au this system has E_bin_=10^41^erg, making it the lowest binding energy system of any pair with M_tot_<0.1M_{sun}_ not associated with a young cluster. It is equivalent in estimated mass ratio, E_bin_, and physical separation to the ~2Myr M7.25+M8.25 binary brown dwarf 2MASS J11011926-7732383AB (2M1101AB) found in the Chameleon star-forming region. W2150AB is the widest companion system yet observed in the field where the primary is an L dwarf or later.
22637. Very low mass objects in ONC
- ID:
- ivo://CDS.VizieR/J/A+A/515/A13
- Title:
- Very low mass objects in ONC
- Short Name:
- J/A+A/515/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Angular momentum (J) loss requires magnetic interaction between the forming star and both the circumstellar disk and the magnetically driven outflows. In order to test these predictions many authors have investigated a rotation-disk connection in pre-main sequence objects with masses larger than about 0.4M_{sun}_. For brown dwarfs (BDs) this connection was not investigated as yet because there are very few samples available. We aim to extend this investigation well down into the substellar regime for our large sample of ~~80 BDs in the Orion Nebula Cluster, for which we have recently measured rotational periods.
- ID:
- ivo://CDS.VizieR/J/A+AS/100/607
- Title:
- Very low mass proper motion members in Pleiades
- Short Name:
- J/A+AS/100/607
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A proper motion membership list is presented for the lower mass stars in the Pleiades open cluster based on a survey of about a 5x5{deg} area around the cluster center. Finder charts prepared from an R passband Schmidt plate are given. Photographic R and I photometry is given for all stars; where possible a V magnitude is also listed. The photometry is accurate to about 0.1mag.
- ID:
- ivo://CDS.VizieR/J/A+AS/109/29
- Title:
- Very low mass stars in Praesepe
- Short Name:
- J/A+AS/109/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a deep proper motion survey of a 19 square degree area of the Galactic open cluster Praesepe. Details of the astrometric and photometric reductions are given, along with the selection process for members. A list of these probable members, along with cross identifications from previous less sensitive surveys, is presented and finder charts given in an Appendix.
- ID:
- ivo://CDS.VizieR/J/A+A/510/A27
- Title:
- Very low mass stars in Praesepe
- Short Name:
- J/A+A/510/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determination of the mass functions of open clusters of different ages allows us to infer the efficiency with which brown dwarfs are evaporated from clusters to populate the field. In this paper we present the results of a photometric survey to identify low mass and brown dwarf members of the old open cluster Praesepe (age 590^+150^_-120_Myr, distance 190^+6.0^_-5.8_pc) from which we estimate its mass function and compare this with that of other clusters. We performed an optical (Ic-band) and near-infrared (J and Ks-band) photometric survey of Praesepe covering 3.1{deg}^2^. With 5sigma detection limits of Ic=23.4 and J=20.0, our survey is predicted to be sensitive to objects with masses from 0.6 to 0.05M_{sun}.
