- ID:
- ivo://CDS.VizieR/J/ApJ/632/894
- Title:
- Blue stragglers, HB and turnoff stars in 4 GC
- Short Name:
- J/ApJ/632/894
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic analysis of HST STIS and FOS low- and intermediate-resolution spectroscopy of 55 stars in four globular clusters (47 Tucanae, M3, NGC 6752, and NGC 6397). Stars hotter than T_eff_=5750K and with a signal-to-noise ratio larger than 15 were analyzed with non-local thermodynamic equilibrium model atmospheres, and values for their effective temperatures and gravities were obtained. Using photometric fluxes, we also obtained radii, luminosities, and spectroscopic masses. Twenty-four stars in our sample are blue stragglers (BSs). Their photometric colors and magnitudes place these BSs above and redward of the clusters' zero-age main sequence: this is consistent with the gravities we find for these stars, which are lower than zero-age main-sequence gravities. A comparison with stellar evolutionary tracks shows that almost all of our BSs are in the Hertzsprung gap. This is contrary to theory, because of the short timescale expected for stars in this evolutionary phase. The mean BS mass is 1.04M_{sun}_for 14 nonvariable stars, or 1.07M_{sun}_counting all 24 BSs in our sample. For the nonvariable stars the mean BS masses for individual clusters are 1.73, 1.01, 0.95, and 0.72M_{sun}_for NGC 6397, NGC 6752, 47 Tuc, and M3, respectively. Adding the variable stars (which improves the statistics but increases the uncertainty), the mean masses become 1.27, 1.05, 0.99, and 0.99M_{sun}_, respectively. Although there is considerable scatter, the BS spectroscopic masses correlate with both effective temperature and brightness of the stars, as expected. The mean nonvariable turnoff star mass (0.58M_{sun}_) is significantly below the values determined for the BSs and below the main-sequence turnoff mass. The mean nonvariable horizontal-branch (HB) star mass is higher than expected (0.79M_{sun}_). In particular, several HB stars have masses well above the main-sequence turnoff mass. Some of these HB stars are suspected of actually being BSs, since most of them reside at ambiguous locations on the CMD, making them prone to misclassification. Values and limits to the stellar rotation rates (vsini) are imposed by fitting weak metal lines, the Ca II K line wings, or the helium lines for the hotter stars. Five BSs with reasonably constrained rotations show average and median vsini values of 109 and 100km/s, respectively, suggesting v~160km/s. At least some GC BSs are very rapid rotators, but this information cannot yet constrain their origin as stellar collision or binary mergers because of the lack of clear theoretical predictions. Six extreme HB stars have rotation rates vsini between 50 and 200km/s, which are high for these stars and might indicate a binary origin. De Marco et al. found that four BSs and two HB stars in our sample have Balmer jumps that are too large for the effective temperatures implied by the slopes of their Paschen continua. Two additional HB stars are now identified in the current study as having the same feature. For these stars, the presence of a disk of partly ionized material is suspected, although high stellar rotation rates could also partly explain the data.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/507/1699
- Title:
- Blue straggler stars in open clusters with Gaia
- Short Name:
- J/MNRAS/507/1699
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Blue straggler stars (BSSs) are the most massive stars in a cluster formed via binary or higher-order stellar interactions. Though the exact nature of such formation scenarios is difficult to pin down, we provide observational constraints on the different possible mechanism. In this quest, we first produce a catalogue of BSSs using Gaia DR2 data. Among the 670 clusters older than 300Myr, we identified 868 BSSs in 228 clusters and 500 BSS candidates in 208 clusters. In general, all clusters older than 1Gyr and massive than 1000M_{sun}_ have BSSs. The average number of BSSs increases with cluster age and mass, and there is a power-law relation between the cluster mass and the maximum number of BSSs in the cluster. We introduce the term fractional mass excess (Me) for BSSs. We find that at least 54% of BSSs have Me<0.5 (likely to have gained mass through a binary mass transfer (MT)), 30% in the 1.0<Me<0.5 range (likely to have gained mass through a merger) and up to 16% with Me>1.0 (likely from multiple mergers/MT). We also find that the percentage of low Me BSSs increases with age, beyond 1-2Gyr, suggesting an increase in formation through MT in older clusters. The BSSs are radially segregated, and the extent of segregation depends on the dynamical relaxation of the cluster. The statistics and trends presented here are expected to constrain the BSS formation models in open clusters.
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/3073
- Title:
- CALIFA galaxies hosting an AGN
- Short Name:
- J/MNRAS/492/3073
- Date:
- 02 Feb 2022 07:33:25
- Publisher:
- CDS
- Description:
- We study the presence of optically-selected Active Galactic Nuclei (AGNs) within a sample of 867 galaxies extracted from the extended Calar-Alto Legacy Integral Field spectroscopy Area (eCALIFA) spanning all morphological classes. We identify 10 Type-I and 24 Type-II AGNs, amounting to ~4 per cent of our sample, similar to the fraction reported by previous explorations in the same redshift range. We compare the integrated properties of the ionized and molecular gas, and stellar population of AGN hosts and their non-active counterparts, combining them with morphological information. The AGN hosts are found in transitory parts (i.e. green-valley) in almost all analysed properties which present bimodal distributions (i.e. a region where reside star-forming galaxies and another with quiescent/retired ones). Regarding morphology, we find AGN hosts among the most massive galaxies, with enhanced central stellar-mass surface density in comparison to the average population at each morphological type. Moreover, their distribution peaks at the Sab-Sb classes and none are found among very late-type galaxies (>Scd). Finally, we inspect how the AGN could act in heir hosts regarding the quenching of star-formation. The main role of the AGN in the quenching process appears to be the removal (or heating) of molecular gas, rather than an additional suppression of the already observed decrease of the star-formation efficiency from late-to-early type galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/848/87
- Title:
- CALIFA SFRs. II. Bulges, bars & disks
- Short Name:
- J/ApJ/848/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We estimate the current extinction-corrected H{alpha} star formation rate (SFR) of the different morphological components that shape galaxies (bulges, bars, and disks). We use a multicomponent photometric decomposition based on Sloan Digital Sky Survey imaging to Calar Alto Legacy Integral Field Area Integral Field Spectroscopy (IFS) datacubes for a sample of 219 galaxies. This analysis reveals an enhancement of the central SFR and specific SFR (sSFR = SFR/M*) in barred galaxies. Along the main sequence, we find that more massive galaxies in total have undergone efficient suppression (quenching) of their star formation, in agreement with many studies. We discover that more massive disks have had their star formation quenched as well. We evaluate which mechanisms might be responsible for this quenching process. The presence of type 2 AGNs plays a role at damping the sSFR in bulges and less efficiently in disks. Also, the decrease in the sSFR of the disk component becomes more noticeable for stellar masses around 10^10.5^M_{sun}_; for bulges, it is already present at ~10^9.5^M_{sun}_. The analysis of the line- of-sight stellar velocity dispersions ({sigma}) for the bulge component and of the corresponding Faber-Jackson relation shows that AGNs tend to have slightly higher {sigma} values than star-forming galaxies for the same mass. Finally, the impact of environment is evaluated by means of the projected galaxy density, {Sigma}5. We find that the SFR of both bulges and disks decreases in intermediate- to high-density environments. This work reflects the potential of combining IFS data with 2D multicomponent decompositions to shed light on the processes that regulate the SFR.
- ID:
- ivo://CDS.VizieR/J/AJ/154/108
- Title:
- California-Kepler Survey (CKS). II. Properties
- Short Name:
- J/AJ/154/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar and planetary properties for 1305 Kepler Objects of Interest hosting 2025 planet candidates observed as part of the California-Kepler Survey. We combine spectroscopic constraints, presented in Paper I, with stellar interior modeling to estimate stellar masses, radii, and ages. Stellar radii are typically constrained to 11%, compared to 40% when only photometric constraints are used. Stellar masses are constrained to 4%, and ages are constrained to 30%. We verify the integrity of the stellar parameters through comparisons with asteroseismic studies and Gaia parallaxes. We also recompute planetary radii for 2025 planet candidates. Because knowledge of planetary radii is often limited by uncertainties in stellar size, we improve the uncertainties in planet radii from typically 42% to 12%. We also leverage improved knowledge of stellar effective temperature to recompute incident stellar fluxes for the planets, now precise to 21%, compared to a factor of two when derived from photometry.
- ID:
- ivo://CDS.VizieR/J/AJ/155/48
- Title:
- California-Kepler Survey (CKS). V. Masses and radii
- Short Name:
- J/AJ/155/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have established precise planet radii, semimajor axes, incident stellar fluxes, and stellar masses for 909 planets in 355 multi-planet systems discovered by Kepler. In this sample, we find that planets within a single multi-planet system have correlated sizes: each planet is more likely to be the size of its neighbor than a size drawn at random from the distribution of observed planet sizes. In systems with three or more planets, the planets tend to have a regular spacing: the orbital period ratios of adjacent pairs of planets are correlated. Furthermore, the orbital period ratios are smaller in systems with smaller planets, suggesting that the patterns in planet sizes and spacing are linked through formation and/or subsequent orbital dynamics. Yet, we find that essentially no planets have orbital period ratios smaller than 1.2, regardless of planet size. Using empirical mass-radius relationships, we estimate the mutual Hill separations of planet pairs. We find that 93% of the planet pairs are at least 10 mutual Hill radii apart, and that a spacing of ~20 mutual Hill radii is most common. We also find that when comparing planet sizes, the outer planet is larger in 65%+/-0.4% of cases, and the typical ratio of the outer to inner planet size is positively correlated with the temperature difference between the planets. This could be the result of photo-evaporation.
- ID:
- ivo://CDS.VizieR/J/AJ/156/264
- Title:
- California-Kepler Survey. VII. Planet radius gap
- Short Name:
- J/AJ/156/264
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of planet sizes encodes details of planet formation and evolution. We present the most precise planet size distribution to date based on Gaia parallaxes, Kepler photometry, and spectroscopic temperatures from the California-Kepler Survey. Previously, we measured stellar radii to 11% precision using high-resolution spectroscopy; by adding Gaia astrometry, the errors are now 3%. Planet radius measurements are, in turn, improved to 5% precision. With a catalog of ~1000 planets with precise properties, we probed in fine detail the gap in the planet size distribution that separates two classes of small planets, rocky super-Earths and gas-dominated sub-Neptunes. Our previous study and others suggested that the gap may be observationally under-resolved and inherently flat-bottomed, with a band of forbidden planet sizes. Analysis based on our new catalog refutes this; the gap is partially filled in. Two other important factors that sculpt the distribution are a planet's orbital distance and its host-star mass, both of which are related to a planet's X-ray/UV irradiation history. For lower-mass stars, the bimodal planet distribution shifts to smaller sizes, consistent with smaller stars producing smaller planet cores. Details of the size distribution including the extent of the "sub-Neptune desert" and the width and slope of the gap support the view that photoevaporation of low-density atmospheres is the dominant evolutionary determinant of the planet size distribution.
- ID:
- ivo://CDS.VizieR/J/AJ/156/254
- Title:
- California-Kepler Survey.VI. Kepler multis & singles
- Short Name:
- J/AJ/156/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The California-Kepler Survey (CKS) catalog contains precise stellar and planetary properties for the Kepler planet candidates, including systems with multiple detected transiting planets ("multis") and systems with just one detected transiting planet ("singles", although additional planets could exist). We compared the stellar and planetary properties of the multis and singles in a homogeneous subset of the full CKS-Gaia catalog. We found that sub-Neptune-sized singles and multis do not differ in their stellar properties or planet radii. In particular: (1) The distributions of stellar properties M_*_, [Fe/H], and vsini for the Kepler sub-Neptune-sized singles and multis are statistically indistinguishable. (2) The radius distributions of the sub-Neptune-sized singles and multis with P>3 days are indistinguishable, and both have a valley at ~1.8 R_{Earth}_. However, there are significantly more detected short-period (P<3 days), sub-Neptune-sized singles than multis. The similarity of the host-star properties, planet radii, and radius valley for singles and multis suggests a common origin. The similar radius valley, which is likely sculpted by photo-evaporation from the host star within the first 100 Myr, suggests that planets in both singles and multis spend much of the first 100 Myr near their present, close-in locations. One explanation that is consistent with the similar fundamental properties of singles and multis is that many of the singles are members of multi-planet systems that underwent planet-planet scattering.
- ID:
- ivo://CDS.VizieR/J/ApJ/770/90
- Title:
- Candidate planets in the habitable zones
- Short Name:
- J/ApJ/770/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A key goal of the Kepler mission is the discovery of Earth-size transiting planets in "habitable zones" where stellar irradiance maintains a temperate climate on an Earth-like planet. Robust estimates of planet radius and irradiance require accurate stellar parameters, but most Kepler systems are faint, making spectroscopy difficult and prioritization of targets desirable. The parameters of 2035 host stars were estimated by Bayesian analysis and the probabilities p_HZ_ that 2738 candidate or confirmed planets orbit in the habitable zone were calculated. Dartmouth Stellar Evolution Program models were compared to photometry from the Kepler Input Catalog, priors for stellar mass, age, metallicity and distance, and planet transit duration. The analysis yielded probability density functions for calculating confidence intervals of planet radius and stellar irradiance, as well as p_HZ_. Sixty-two planets have p_HZ_>0.5 and a most probable stellar irradiance within habitable zone limits. Fourteen of these have radii less than twice the Earth; the objects most resembling Earth in terms of radius and irradiance are KOIs 2626.01 and 3010.01, which orbit late K/M-type dwarf stars. The fraction of Kepler dwarf stars with Earth-size planets in the habitable zone ({eta}_{Earth}_) is 0.46, with a 95% confidence interval of 0.31-0.64. Parallaxes from the Gaia mission will reduce uncertainties by more than a factor of five and permit definitive assignments of transiting planets to the habitable zones of Kepler stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/281
- Title:
- Candidate rotating M dwarfs from PS1-MDS
- Short Name:
- J/ApJ/833/281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on an ongoing project to investigate activity in the M dwarf stellar population observed by the Pan-STARRS1 Medium-Deep Survey (PS1-MDS). Using a custom-built pipeline, we refine an initial sample of ~4 million sources in PS1-MDS to a sample of 184148 candidate cool stars using color cuts. Motivated by the well-known relationship between rotation and stellar activity, we use a multiband periodogram analysis and visual vetting to identify 270 sources that are likely rotating M dwarfs. We derive a new set of polynomials relating M dwarf PS1 colors to fundamental stellar parameters and use them to estimate the masses, distances, effective temperatures, and bolometric luminosities of our sample. We present a catalog containing these values, our measured rotation periods, and cross-matches to other surveys. Our final sample spans periods of <~1-130 days in stars with estimated effective temperatures of ~2700-4000K. Twenty-two of our sources have X-ray cross-matches, and they are found to be relatively X-ray bright as would be expected from selection effects. Our data set provides evidence that Kepler-based searches have not been sensitive to very slowly rotating stars (P_rot_>~70 day), implying that the observed emergence of very slow rotators in studies of low-mass stars may be a systematic effect. We also see a lack of low-amplitude (<2%) variability in objects with intermediate (10-40 day) rotation periods, which, considered in conjunction with other observational results, may be a signpost of a loss of magnetic complexity associated with a phase of rapid spin-down in intermediate-age M dwarfs. This work represents just a first step in exploring stellar variability in data from the PS1-MDS and, in the farther future, Large Synoptic Survey Telescope.
