- ID:
- ivo://CDS.VizieR/J/MNRAS/485/2312
- Title:
- Outer Galactic disk A and F stars space motions
- Short Name:
- J/MNRAS/485/2312
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A and F stars can be used as probes of outer Galactic disk kinematics: here we extend the work of Harris et al. (2018, Cat. J/MNRAS/475/1680) by crossmatching their A/F sample with Gaia DR2 to bring in proper motions. These are combined with the already measured radial velocities and spectro-photometric distances to obtain full space motions. We use this sample of 1173 stars, located in two pencil-beam sightlines (l=178{deg} and l=118{deg}), to sample the Galactocentric velocity field out to almost R_G_=15kpc. We find there are significant differences in all three (radial, azimuthal and vertical) kinematic components between the two directions. The rotation curve is roughly flat in the anticentre direction, confirming and extending the result of Kawata et al. (2018MNRAS.479L.108K) thanks to the greater reach of our spectro-photometric distance scale. However at l=118{deg} the circular velocity rises outwards from R_G_=10.5kpc and there is a more pronounced gradient in radial motion than is seen at l=178{deg}. Furthermore, the A star radial motion differs from the F stars by ~10km/s. We discuss our findings in the context of perturbers potentially responsible for the trends, such as the central bar, spiral arms, the warp and external satellites. Our results at l=178{deg} are broadly consistent with previous work on K giants in the anticentre, but the kinematics at l=118{deg} in the Perseus region do not yet reconcile easily with bar or spiral arm perturbation.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/3301
- Title:
- Oxygen abundance in Galactic disc Cepheids
- Short Name:
- J/MNRAS/444/3301
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed a non-local thermodynamic equilibrium (NLTE) analysis of the infrared oxygen triplet for a large number of Cepheid spectra obtained with the Hobby-Eberly Telescope. These data were combined with our previous NLTE results for stars observed with the Max Planck Gesellschaft Telescope with the aim of investigating the oxygen abundance distribution in the Galactic thin disc. We found the slope of the radial (O/H) distribution to be equal -0.058dex/kpc. However, we found some evidence that the distribution might become flatter in the outer parts of the disc. This is supported by the results of other authors who have studied open clusters, planetary nebulae and Hii regions. Some mechanisms of flattening are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/616/L15
- Title:
- Parallaxes and Proper Motions of OB stars
- Short Name:
- J/A+A/616/L15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors less than 10%; (2) only O-type stars with 0.1mas errors imposed and with parallax distance errors less than 0.2kpc; (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors less than 0.3kpc. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4kpc,the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.
- ID:
- ivo://CDS.VizieR/J/ApJ/783/130
- Title:
- Parallaxes of high mass star forming regions
- Short Name:
- J/ApJ/783/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Over 100 trigonometric parallaxes and proper motions for masers associated with young, high-mass stars have been measured with the Bar and Spiral Structure Legacy Survey, a Very Long Baseline Array key science project, the European VLBI Network, and the Japanese VLBI Exploration of Radio Astrometry project. These measurements provide strong evidence for the existence of spiral arms in the Milky Way, accurately locating many arm segments and yielding spiral pitch angles ranging from about 7{deg} to 20{deg}. The widths of spiral arms increase with distance from the Galactic center. Fitting axially symmetric models of the Milky Way with the three-dimensional position and velocity information and conservative priors for the solar and average source peculiar motions, we estimate the distance to the Galactic center, R_0_, to be 8.34+/-0.16kpc, a circular rotation speed at the Sun, {Theta}_0_, to be 240+/-8km/s, and a rotation curve that is nearly flat (i.e., a slope of -0.2+/-0.4km/s/kpc) between Galactocentric radii of {approx}5 and 16kpc. Assuming a "universal" spiral galaxy form for the rotation curve, we estimate the thin disk scale length to be 2.44+/-0.16kpc. With this large data set, the parameters R_0_ and {Theta}_0_are no longer highly correlated and are relatively insensitive to different forms of the rotation curve. If one adopts a theoretically motivated prior that high-mass star forming regions are in nearly circular Galactic orbits, we estimate a global solar motion component in the direction of Galactic rotation, V_{sun}_=14.6+/-5.0km/s. While {Theta}_0_and V_{sun}_are significantly correlated, the sum of these parameters is well constrained, {Theta}_0_+V_{sun}_=255.2+/-5.1km/s, as is the angular speed of the Sun in its orbit about the Galactic center, ({Theta}_0_+V_{sun}_)/R_0_=30.57+/-0.43km/s/kpc. These parameters improve the accuracy of estimates of the accelerations of the Sun and the Hulse-Taylor binary pulsar in their Galactic orbits, significantly reducing the uncertainty in tests of gravitational radiation predicted by general relativity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/1680
- Title:
- Parameters of 1183 A and F stars
- Short Name:
- J/MNRAS/475/1680
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies of the rotation law in the outer Galactic disc have mainly used gas tracers or clump giants. Here, we explore A and F stars as alternatives: these provide a much denser sampling in the outer disc than gas tracers and have experienced significantly less velocity scattering than older clump giants. This first investigation confirms the suitability of A stars in this role. Our work is based on spectroscopy of roughly 1300 photometrically selected stars in the red calcium-triplet region, chosen to mitigate against the effects of interstellar extinction. The stars are located in two low Galactic latitude sightlines, at longitudes l=118{deg}, sampling strong Galactic rotation shear, and l=178{deg}, near the anticentre. With the use of Markov Chain Monte Carlo parameter fitting, stellar parameters and radial velocities are measured, and distances computed. The obtained trend of radial velocity with distance is inconsistent with existing flat or slowly rising rotation laws from gas tracers (Brand & Blitz, 1993A&A...275...67B, Cat J/A+A/275/67; Reid et al., 2014ApJ...783..130R, Cat. J/ApJ/783/130). Instead, our results fit in with those obtained by Huang et al. (2016MNRAS.463.2623H) from disc clump giants that favoured rising circular speeds. An alternative interpretation in terms of spiral arm perturbation is not straight forward. We assess the role that undetected binaries in the sample and distance error may have in introducing bias, and show that the former is a minor factor. The random errors in our trend of circular velocity are within +/-5km/s.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/L26
- Title:
- Parameters of radio sources near Sgr A*
- Short Name:
- J/ApJ/801/L26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present radio images within 30" of Sgr A* based on recent VLA observations at 34 GHz with 7.8 {mu}Jy sensitivity and resolution of ~88x46 mas. We report 44 partially resolved compact sources clustered in two regions in the E arm of ionized gas that orbits Sgr A*. These sources have size scales ranging between ~50 and 200 mas (400-1600 AUs), and a bow-shock appearance facing the direction of Sgr A*. Unlike the bow-shock sources previously identified in the near-IR but associated with massive stars, these 34 GHz sources do not appear to have near-IR counterparts at 3.8 {mu}m. We interpret these sources as a candidate population of photoevaporative protoplanetary disks (proplyds) that are associated with newly formed low mass stars with mass loss rates ~10^-7^-10^-6^ M_{sun}_/yr and are located at the edge of a molecular cloud outlined by ionized gas. The disks are externally illuminated by strong Lyman continuum radiation from the ~100 OB and WR massive stars distributed within 10" of Sgr A*. The presence of proplyds implies current in situ star formation activity near Sgr A* and opens a window for the first time to study low mass star, planetary, and brown dwarf formations near a supermassive black hole. The video abstract was created from a WorldWide Telescope tour file, which is available for download. Viewing the file requires a Windows PC with the WorldWide Telescope desktop client available at worldwidetelescope.org.
- ID:
- ivo://CDS.VizieR/J/AJ/122/3155
- Title:
- Peculiar HI cloud near galactic plane
- Short Name:
- J/AJ/122/3155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An H I cloud with a double-lobed structure and a radial velocity of +50km/s has been found near l=92{deg}, b=-4{deg} in a low-resolution H I survey carried out at the Dominion Radio Astrophysical Observatory (DRAO). This velocity is forbidden for circular Galactic rotation. Because of its unusual morphology and small variation in radial velocity over the cloud, further observations of the area were made with the DRAO Synthesis Telescope, both in the H I line and in the radio continuum. The cloud has dimensions of about 3.3{deg}x0.5{deg}, and has a morphology somewhat similar to high-velocity H I clouds (HVCs). Several possible associations with other objects are examined in this paper. A variable inverted-spectrum radio continuum source exists near the morphological center of the H I cloud. It is probably a rare example of a gigahertz peaked spectrum (GPS) extragalactic source having a peak above 5GHz. A luminous B star is found close to the peculiar H I cloud, and the cloud is also located near the center of an H I supershell, supposedly located at a distance of about 9kpc. Energetic and other considerations lead to the conclusion that the cloud is probably not related to the HVC phenomenon nor to any of the above objects but is a relic of a nearby (D~1kpc) supernova event, all other evidence of which has now dissipated. Maps of continuum radio emission (at 1420 and 408MHz) in the area around the cloud are presented, as well as lists of continuum radio sources. A few isolated high-velocity knots of H I emission have also been detected in the vicinity of the cloud.
- ID:
- ivo://CDS.VizieR/J/ApJ/793/132
- Title:
- Perseus cloud sources Gaussian parameters
- Short Name:
- J/ApJ/793/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Arecibo Observatory, we have obtained neutral hydrogen (HI) absorption and emission spectral pairs in the direction of 26 background radio continuum sources in the vicinity of the Perseus molecular cloud. Strong absorption lines were detected in all cases, allowing us to estimate spin temperature (T_s_) and optical depth for 107 individual Gaussian components along these lines of sight. Basic properties of individual H I clouds (spin temperature, optical depth, and the column density of the cold and warm neutral medium (CNM and WNM), respectively) in and around Perseus are very similar to those found for random interstellar lines of sight sampled by the Millennium H I survey. This suggests that the neutral gas found in and around molecular clouds is not atypical. However, lines of sight in the vicinity of Perseus have, on average, a higher total H I column density and the CNM fraction, suggesting an enhanced amount of cold H I relative to an average interstellar field. Our estimated optical depth and spin temperature are in stark contrast with the recent attempt at using Planck data to estimate properties of the optically thick H I. Only ~15% of lines of sight in our study have a column density weighted average spin temperature lower than 50 K, in comparison with >~85% of Planck's sky coverage. The observed CNM fraction is inversely proportional to the optical depth weighted average spin temperature, in excellent agreement with the recent numerical simulations by Kim et al. (2014ApJ...786...64K). While the CNM fraction is, on average, higher around Perseus relative to a random interstellar field, it is generally low, between 10%-50%. This suggests that extended WNM envelopes around molecular clouds and/or significant mixing of CNM and WNM throughout molecular clouds are present and should be considered in the models of molecule and star formation. Our detailed comparison of H I absorption with CO emission spectra shows that only 3 of the 26 directions are clear candidates for probing the CO-dark gas as they have N(H I)>10^21^/cm2 yet no detectable CO emission.
- ID:
- ivo://CDS.VizieR/J/AJ/158/219
- Title:
- Phosphorus abundances in the Hyades and Galactic disk
- Short Name:
- J/AJ/158/219
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured phosphorus abundances in nine disk stars between -1< [Fe/H]< -0.5 and in 12 members of the Hyades open cluster using two P I lines at 1.06 {mu}m. High-resolution infrared spectra were obtained using Phoenix on Gemini South and abundances were determined by comparing synthetic spectra to the observations. The average abundance for the dwarf stars in our Hyades sample was <[P/Fe]>=-0.01+/-0.06 and <[P/Fe]>=0.03+/-0.03 dex for the three giants. The consistency suggests that abundances derived using the 1.06 {mu}m P I lines are not subjected to temperature- or luminosity-dependent systematic effects at high metallicities. Our [P/Fe] ratios measured in disk stars are consistent with chemical evolution models with P yields increased by a factor of 2.75. We find that [P/O], [P/Mg], [P/Si], and [P/Ti] ratios are consistent with the solar ratio over a range of -1.0<[Fe/H]<0.2 with the [P/Si] ratio increasing by ~0.1-0.2 dex at the lowest [Fe/H] ratios. Finally, the evolution of [P/Fe] with age is similar to other {alpha} elements, providing evidence that P is produced at the same sites.
- ID:
- ivo://CDS.VizieR/V/92A
- Title:
- Photometric and Spectroscopic Databases for LSS Stars
- Short Name:
- V/92A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog contains databases of published photoelectric UBVbeta data, MK-system spectral classifications, and Stroemgren four-color uvby photometry for objects in the Stephenson-Sanduleak "Luminous Stars in the Southern Milky Way" catalog (LSS catalog). The catalog contains mostly OB stars and A and F supergiants. These databases have been compiled from the literature.
