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81. ACS VI photometry of M31 halo RR Lyrea
ID:
ivo://CDS.VizieR/J/AJ/127/2738
Title:
ACS VI photometry of M31 halo RR Lyrea
Short Name:
J/AJ/127/2738
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a complete census of RR Lyrae stars in a halo field of the Andromeda galaxy. These deep observations, taken as part of a program to measure the star formation history in the halo, spanned a period of 41 days with sampling on a variety of timescales, enabling the identification of short- and long-period variables. Although the long-period variables cannot be fully characterized within the time span of this program, the enormous advance in sensitivity provided by the Advanced Camera for Surveys on the Hubble Space Telescope allows accurate characterization of the RR Lyrae population in this field. We find 29 RRab stars with a mean period of 0.594 days, 25 RRc stars with a mean period of 0.316 days, and one RRd star with a fundamental period of 0.473 days and a first-overtone period of 0.353 days. These 55 RR Lyrae stars imply a specific frequency S_RR_~5.6, which is large given the high mean metallicity of the halo, but not surprising given that these stars arise from the old, metal-poor tail of the distribution.
82. ACS Virgo Cluster Survey. VI
ID:
ivo://CDS.VizieR/J/ApJS/164/334
Title:
ACS Virgo Cluster Survey. VI
Short Name:
J/ApJS/164/334
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed analysis of the morphology, isophotal parameters, and surface brightness profiles for 100 early-type members of the Virgo Cluster, from dwarfs (M_B_=-15.1mag) to giants (M_B_=-21.8mag), imaged in the g and z passbands using the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope.
83. ACS Virgo Cluster Survey. XIII.
ID:
ivo://CDS.VizieR/J/ApJ/655/144
Title:
ACS Virgo Cluster Survey. XIII.
Short Name:
J/ApJ/655/144
Date:
21 Oct 2021
Publisher:
CDS
Description:
The ACS Virgo Cluster Survey consists of HST-ACS Advance Camera for Surveys) imaging for 100 early-type galaxies in the Virgo Cluster, observed in the F475W (~SDSS g) and F850LP (~SDSS z) filters. We derive distances for 84 of these galaxies using the method of surface brightness fluctuations (SBFs), present the SBF distance catalog, and use this database to examine the three-dimensional distribution of early-type galaxies in the Virgo Cluster. The SBF distance moduli have a mean (random) measurement error of 0.07mag (0.5Mpc), or roughly 3 times better than previous SBF measurements for Virgo Cluster galaxies. Five galaxies lie at a distance of d~23Mpc and are members of the W' cloud. The remaining 79 galaxies have a narrow distribution around our adopted distance of <d>=16.5+/-0.1 (random mean error) +/-1.1Mpc (systematic). The rms distance scatter of this sample is {sigma}(d)=0.6+/-0.1Mpc, with little or no dependence on morphological type or luminosity class (i.e., 0.7+/-0.1 and 0.5+/-0.1Mpc for the giants and dwarfs, respectively). The back-to-front depth of the cluster measured from our sample of early-type galaxies is 2.4+/-0.4Mpc (i.e., +/-2{sigma} of the intrinsic distance distribution). The M87 (cluster A) and M49 (cluster B) subclusters are found to lie at distances of 16.7+/-0.2 and 16.4+/-0.2Mpc, respectively. There may be a third subcluster associated with M86. A weak correlation between velocity and line-of-sight distance may be a faint echo of the cluster velocity distribution not having yet completely virialized. In three dimensions, Virgo's early-type galaxies appear to define a slightly triaxial distribution, with axis ratios of (1:0.7:0.5). The principal axis of the best-fit ellipsoid is inclined ~20{deg}-40{deg} from the line of sight, while the galaxies belonging to the W' cloud lie on an axis inclined by ~10{deg}-15{deg}.
84. ACS Virgo Cluster Survey. XV
ID:
ivo://CDS.VizieR/J/ApJ/681/197
Title:
ACS Virgo Cluster Survey. XV
Short Name:
J/ApJ/681/197
Date:
21 Oct 2021
Publisher:
CDS
Description:
The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey, the largest homogeneous catalog of its kind.
85. Activity and rotation in Praesepe and the Hyades
ID:
ivo://CDS.VizieR/J/ApJ/795/161
Title:
Activity and rotation in Praesepe and the Hyades
Short Name:
J/ApJ/795/161
Date:
21 Oct 2021
Publisher:
CDS
Description:
Open clusters are collections of stars with a single, well-determined age, and can be used to investigate the connections between angular-momentum evolution and magnetic activity over a star's lifetime. We present the results of a comparative study of the relationship between stellar rotation and activity in two benchmark open clusters: Praesepe and the Hyades. As they have the same age and roughly solar metallicity, these clusters serve as an ideal laboratory for testing the agreement between theoretical and empirical rotation-activity relations at ~600 Myr. We have compiled a sample of 720 spectra - more than half of which are new observations - for 516 high-confidence members of Praesepe; we have also obtained 139 new spectra for 130 high-confidence Hyads. We have also collected rotation periods (P_rot_) for 135 Praesepe members and 87 Hyads. To compare H{alpha} emission, an indicator of chromospheric activity, as a function of color, mass, and Rossby number R_o_, we first calculate an expanded set of {chi} values, with which we can obtain the H{alpha} to bolometric luminosity ratio, L_H{alpha}_/L_bol_, even when spectra are not flux-calibrated and/or stars lack reliable distances. Our {chi} values cover a broader range of stellar masses and colors (roughly equivalent to spectral types from K0 to M9), and exhibit better agreement between independent calculations, than existing values. Unlike previous authors, we find no difference between the two clusters in their H{alpha} equivalent width or L_H{alpha}_/L_bol_ distributions, and therefore take the merged H{alpha} and P_rot_ data to be representative of 600 Myr old stars. Our analysis shows that H{alpha} activity in these stars is saturated for R_O_<=0.11\-0.03_^+0.02^. Above that value activity declines as a power-law with slope {beta}=0.73_-0.12_^+0.16^, before dropping off rapidly at R_o_{approx} 0.4. These data provide a useful anchor for calibrating the age-activity-rotation relation beyond 600 Myr.
86. Activity cycles in 3203 Kepler stars
ID:
ivo://CDS.VizieR/J/A+A/603/A52
Title:
Activity cycles in 3203 Kepler stars
Short Name:
J/A+A/603/A52
Date:
21 Oct 2021
Publisher:
CDS
Description:
In recent years it has been claimed that the length of stellar activity cycles is determined by the stellar rotation rate. It has been observed that the cycle period increases with rotation period along two distinct sequences, known as the active and inactive sequences. In this picture the Sun occupies a solitary position between the two sequences. Whether the Sun might undergo a transitional evolutionary stage is currently under debate. Our goal is to measure cyclic variations of the stellar light curve amplitude and the rotation period using four years of Kepler data. Periodic changes in the light curve amplitude or the stellar rotation period are associated with an underlying activity cycle. Using a recent sample of active stars we compute the rotation period and the variability amplitude for each individual Kepler quarter and search for periodic variations of both time series. To test for periodicity in each stellar time series we consider Lomb-Scargle periodograms and use a selection based on a false alarm probability (FAP). We detect amplitude periodicities in 3203 stars between 0.5-6 years covering rotation periods between 1-40 days. Given our sample size of 23,601 stars and our selection criteria that the FAP is less than 5%, this number is almost three times higher than that expected from pure noise. We do not detect periodicities in the rotation period beyond those expected from noise. Our measurements reveal that the cycle period shows a weak dependence on rotation rate, slightly increasing for longer rotation periods. We further show that the shape of the variability deviates from a pure sine curve, consistent with observations of the solar cycle. The cycle shape does not show a statistically significant dependence on effective temperature. We detect activity cycles in more than 13% of our final sample with a FAP of 5% (calculated by randomly shuffling the measured 90-day variability measurements for each star). Our measurements do not support the existence of distinct sequences in the Prot-Pcyc plane, although there is some evidence for the inactive sequence for rotation periods between 5-25 days. Unfortunately,the total observing time is too short to draw sound conclusions on activity cycles with similar lengths to that of the solar cycle.
87. Activity of bright solar analogs
ID:
ivo://CDS.VizieR/J/AJ/138/312
Title:
Activity of bright solar analogs
Short Name:
J/AJ/138/312
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 14 years of contemporaneous photometric and spectroscopic observations of 28 solar analog stars, taken with the Tennessee State University Automatic Photometric Telescopes at Fairborn Observatory and the Solar-Stellar Spectrograph at Lowell Observatory. These are the best observed and most nearly Sun-like of the targets in our magnitude-limited (V<=7.5) sample. The correlations between luminosity and activity reveal the expected inverse activity-brightness correlations for active stars. Strong direct correlations between activity and brightness are not prevalent for the less active solar age stars, but are precision limited.
88. Activity-rotation relationship in stars
ID:
ivo://CDS.VizieR/J/A+A/397/147
Title:
Activity-rotation relationship in stars
Short Name:
J/A+A/397/147
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a new study on the relationship between coronal X-ray emission and stellar rotation in late-type main-sequence stars. We have selected a sample of 259 dwarfs in the B-V range 0.5-2.0, including 110 field stars and 149 members of the Pleiades, Hyades, {alpha} Persei, IC 2602 and IC 2391 open clusters. All the stars have been observed with ROSAT, and most of them have photometrically-measured rotation periods available. Our results confirm that two emission regimes exist, one in which the rotation period is a good predictor of the total X-ray luminosity, and the other in which a constant saturated X-ray to bolometric luminosity ratio is attained; we present a quantitative estimate of the critical rotation periods below which stars of different masses (or spectral types) enter the saturated regime.
89. Activity type of AGN with SDSS spectra
ID:
ivo://CDS.VizieR/J/other/Ap/63.322
Title:
Activity type of AGN with SDSS spectra
Short Name:
J/other/Ap/63.32
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is a detailed spectral classification of 96 active galaxies from the Veron-Cetty and Veron catalog (2010, Version 13, Cat. VII/258) of active galaxies and quasars. These objects were identified as radio sources using standard radio catalogs. Those galaxies which had radio sources in at least 6 different radio bands and had been identified spectrally in the SDSS catalog were selected. The types of activity of these were determined using their SDSS spectra. Three diagnostic diagrams and a direct study of the spectra were used for more certain classification. As a result, the classifications of 85% of the objects were changed. The radio sources in different radio bands make it possible to construct the spectral distribution of the energy in the radio range and to compare it with the optical activity types.
90. Activity types of ROSAT/SDSS galaxies
ID:
ivo://CDS.VizieR/J/other/Ap/62.147
Title:
Activity types of ROSAT/SDSS galaxies
Short Name:
J/other/Ap/62.14
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this study we carry out detailed spectral classification of 173 AGN candidates from the Joint HRC/BHRC sample, which is a combination of HRC (Hamburg-ROSAT Catalogue) and BHRC (Byurakan-Hamburg-ROSAT Catalogue). These objects were revealed as optical counterparts for ROSAT X-ray sources, however spectra for 173 of them are given in SDSS without definite spectral classification. We studied these 173 objects using the SDSS spectra and revealed the detailed activity types for them. Three diagnostic diagrams and direct examination of the spectra were used to have more confident classification. We also made identification of these sources in other wavelength ranges and calculated some of their parameters.