Search

Start Over Subject optical astronomy
3541. Stars and globulars in NGC4494
ID:
ivo://CDS.VizieR/J/MNRAS/415/3393
Title:
Stars and globulars in NGC4494
Short Name:
J/MNRAS/415/3393
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a comprehensive analysis of the spatial, kinematic and chemical properties of stars and globular clusters (GCs) in the 'ordinary' elliptical galaxy NGC 4494 using data from the Keck and Subaru telescopes. We derive galaxy surface brightness and colour profiles out to large galactocentric radii. We compare the latter to metallicities derived using the near-infrared Calcium Triplet. We obtain stellar kinematics out to ~3.5 effective radii.
3542. Stars associated to Eagle Nebula (M16=NGC6611)
ID:
ivo://CDS.VizieR/J/A+A/521/A61
Title:
Stars associated to Eagle Nebula (M16=NGC6611)
Short Name:
J/A+A/521/A61
Date:
21 Oct 2021
Publisher:
CDS
Description:
Massive star-forming regions are characterized by intense ionizing fluxes, strong stellar winds and, occasionally, supernovae explosions, all of which have important effects on the surrounding media, on the star-formation process and on the evolution of young stars and their circumstellar disks. We present a multiband study of the massive young cluster NGC 6611 and its parental cloud (the Eagle Nebula) with the aim of studying how OB stars affect the early stellar evolution and the formation of other stars. We search for evidence of triggering of star formation by the massive stars inside NGC 6611 on a large spatial scale (~10 parsec) and ongoing disk photoevaporation in NGC 6611 and how its efficiency depends on the mass of the central stars.
3543. Stars in the Carina dSph galaxy field
ID:
ivo://CDS.VizieR/J/AJ/130/2677
Title:
Stars in the Carina dSph galaxy field
Short Name:
J/AJ/130/2677
Date:
21 Oct 2021
Publisher:
CDS
Description:
The question of the existence of active and prominent tidal disruption around various Galactic dwarf spheroidal (dSph) galaxies remains controversial. That debate often centers on the nature (bound vs. unbound) of extended populations of stars claimed to lie outside the bounds of single King profiles fitted to the density distributions of dSph centers. However, the more fundamental issue of the very existence of the previously reported extended populations is still contentious. We present a critical evaluation of the debate centering on one particular dSph, Carina, for which claims both for and against the existence of stars beyond the King limiting radius have been made.
3544. Stars in the dark cloud L1251
ID:
ivo://CDS.VizieR/J/A+A/272/235
Title:
Stars in the dark cloud L1251
Short Name:
J/A+A/272/235
Date:
21 Oct 2021
Publisher:
CDS
Description:
The distance of the dark cloud L1251 was estimated from observations made at the Konkoly Observatory between 1985 and 1991. The spectral classification and the H{alpha} emission features were measured on objective-prism plates taken with the 60/80/180 Schmidt telescope; the photometry was derived from observations made on photographic plates with emulsion-filter combinations giving magnitudes in the Johnson photometric system. The distance of the cloud was found to be 300+/-50pc.
3545. Stars in the solar region
ID:
ivo://CDS.VizieR/J/AJ/115/2397
Title:
Stars in the solar region
Short Name:
J/AJ/115/2397
Date:
21 Oct 2021
Publisher:
CDS
Description:
Several samples of nearby stars with the most accurate astrometric and photometric parameters are searched for clues to their evolutionary history. The main samples are (1) the main-sequence stars with b-y between 0.29 and 0.59mag (F3 to K1) in the Yale parallax catalog, (2) a group of high-velocity subgiants studied spectroscopically by Ryan & Lambert (1995AJ....109.2068R), and (3) high-velocity main-sequence stars in the extensive investigation by Norris, Bessel, & Pickles (1985ApJS...58..463N). The major conclusions are as follows: (1) The oldest stars (halo), t>=10-12Gyr, have V-velocities (in the direction of Galactic rotation and referred to the Sun) in the range from about -50 to -800km/s and have a heavy-element abundance [Fe/H] of less than about -0.8dex. The age range of these objects depends on our knowledge of globular cluster ages, but if age is correlated with V-velocity, the youngest may be M22 and M28 (V~-50km/s) and the oldest NGC 3201 (V~-500km/s) and assorted field stars. (2) The old disk population covers the large age range from about 2Gyr (Hyades, NGC 752) to 10 or 12Gyr (Arcturus group, 47 Tuc), but the lag (V) velocity is restricted to less than about 120km/s and [Fe/H]>=-0.8 or -0.9dex. The [Fe/H]~-0.8dex division between halo and old disk, near t~10-12Gyr, is marked by a change in the character of the CN index (Cm) and of the blanketing parameter K of the DDO photometry. (3) The young disk population, t<2Gyr, is confined exclusively to a well-defined area of the (U, V) velocity plane. The age separating young and old disk stars is also that separating giant evolution of the Hyades (near main-sequence luminosity) and M67 (degenerate helium cores and a large luminosity rise) kinds. The two disk populations are also separated by such indexes as the g-index of Geveva photometry. There appears to be no obvious need to invoke exogeneous influences to understand the motion and heavy-element abundance distributions of the best-observed stars near the Sun. Individual stars of special interest include the parallax star HD 55575, which may be an equal-component binary, and the high-velocity star HD 220127, with a well-determined space velocity near 1000km/s.
3546. Stars nearby Robo-AO Kepler planetary candidates
ID:
ivo://CDS.VizieR/J/AJ/155/161
Title:
Stars nearby Robo-AO Kepler planetary candidates
Short Name:
J/AJ/155/161
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the overall statistical results from the Robo-AO Kepler planetary candidate survey, comprising of 3857 high-angular resolution observations of planetary candidate systems with Robo-AO, an automated laser adaptive optics system. These observations reveal previously unknown nearby stars blended with the planetary candidate host stars that alter the derived planetary radii or may be the source of an astrophysical false positive transit signal. In the first three papers in the survey, we detected 440 nearby stars around 3313 planetary candidate host stars. In this paper, we present observations of 532 planetary candidate host stars, detecting 94 companions around 88 stars; 84 of these companions have not previously been observed in high resolution. We also report 50 more-widely separated companions near 715 targets previously observed by Robo-AO. We derive corrected planetary radius estimates for the 814 planetary candidates in systems with a detected nearby star. If planetary candidates are equally likely to orbit the primary or secondary star, the radius estimates for planetary candidates in systems with likely bound nearby stars increase by a factor of 1.54, on average. We find that 35 previously believed rocky planet candidates are likely not rocky due to the presence of nearby stars. From the combined data sets from the complete Robo-AO KOI survey, we find that 14.5+/-0.5% of planetary candidate hosts have a nearby star with 4", while 1.2% have two nearby stars, and 0.08% have three. We find that 16% of Earth-sized, 13% of Neptune-sized, 14% of Saturn-sized, and 19% of Jupiter-sized planet candidates have detected nearby stars.
3547. Stars of Lyman break galaxies at z~5
ID:
ivo://CDS.VizieR/J/ApJ/693/507
Title:
Stars of Lyman break galaxies at z~5
Short Name:
J/ApJ/693/507
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of spectral energy distribution (SED) fitting analysis for Lyman break galaxies (LBGs) at z~5 in the Great Observatories Origins Deep Survey North (GOODS-N) and its flanking fields (the GOODS-FF). With the publicly available Infrared Array Camera (IRAC) images in the GOODS-N and IRAC data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a large sample (~100) of UV-selected galaxies at z~5. Comparing the observed SEDs with model SEDs generated with a population synthesis code, we derived a best-fit set of parameters (stellar mass, age, color excess, and star formation rate) for each of the sample LBGs. The derived stellar masses range from 10^8^ to 10^11^M_{sun}_ with a median value of 4.1x10^9^M_{sun}_.
3548. Stars within 8 pc of the Sun
ID:
ivo://CDS.VizieR/J/AJ/121/2189
Title:
Stars within 8 pc of the Sun
Short Name:
J/AJ/121/2189
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the technique and results of a survey of stars within 8pc of the Sun with declinations {delta}>-35{deg} (J2000.00). The survey, designed to find without color bias faint companions, consists of optical coronagraphic images of the 1 field of view centered on each star and infrared direct images with a 32" field of view. The images were obtained through the optical Gunn r and z filters and the infrared J and K filters. The survey achieves sensitivities up to 4 absolute magnitudes fainter than the prototype brown dwarf, Gliese 229B. However, this sensitivity varies with the seeing conditions, the intrinsic brightness of the star observed, and the angular distance from the star. As a result, we tabulate sensitivity limits for each star in the survey. We used the criterion of common proper motion to distinguish companions and to determine their luminosities. In addition to the brown dwarf Gl 229B, we have identified six new stellar companions of the sample stars. Since the survey began, accurate trigonometric parallax measurements for most of the stars have become available. As a result, some of the stars we originally included should no longer be included in the 8pc sample. In addition, the 8pc sample is incomplete at the faint end of the main sequence, complicating our calculation of the binary fraction of brown dwarfs. We assess the sensitivity of the survey to stellar companions and to brown dwarf companions of different masses and ages.
3549. Stellar abundances from LAMOST MRS (SPCAnet)
ID:
ivo://CDS.VizieR/J/ApJ/891/23
Title:
Stellar abundances from LAMOST MRS (SPCAnet)
Short Name:
J/ApJ/891/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
The fundamental stellar atmospheric parameters (Teff and logg) and 13 chemical abundances are derived for medium-resolution spectroscopy from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Medium Resolution Survey (MRS) data sets with a deep-learning method. The neural networks we designed, named SPCANet, precisely map LAMOST MRS spectra to stellar parameters and chemical abundances. The stellar labels derived by SPCANet have precisions of 119K for Teff and 0.17dex for logg. The abundance precision of 11 elements including [C/H], [N/H], [O/H], [Mg/H], [Al/H], [Si/H], [S/H], [Ca/H], [Ti/H], [Cr/H], [Fe/H], and [Ni/H] are 0.06 {\sim} 0.12 dex, while that of [Cu/H] is 0.19dex. These precisions can be reached even for spectra with signal-to-noise ratios as low as 10. The results of SPCANet are consistent with those from other surveys such as APOGEE, GALAH, and RAVE, and are also validated with the previous literature values including clusters and field stars.
3550. Stellar activity of late-type stars
ID:
ivo://CDS.VizieR/J/A+AS/142/275
Title:
Stellar activity of late-type stars
Short Name:
J/A+AS/142/275
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results from a spectroscopic CaII H&K survey of 1058 late-type stars selected from a color-limited subsample of the Hipparcos (Cat. <I/239>) catalog. Out of these 1058 stars, 371 stars were found to show significant H&K emission, most of them previously unknown; 23% with strong emission, 36% with moderate emission, and 41% with weak emission. These spectra are used to determine absolute H&K emission-line fluxes, radial velocities, and equivalent widths of the luminosity-sensitive Sr II line at 4077{AA}. Red-wavelength spectroscopic and Stroemgren y photometric follow-up observations of the 371 stars with H&K emission are used to additionally determine the absolute H{alpha}-core flux, the lithium abundance from the Li I 6708{AA} equivalent width, the rotational velocity vsini, the radial velocity, and the light variations and its periodicity.