- ID:
- ivo://CDS.VizieR/J/ApJS/246/15
- Title:
- K2 periodic variables in M35 & NGC2158
- Short Name:
- J/ApJS/246/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 1143 periodic variables, compiled from our image-subtracted photometric analysis of the K2 Campaign-0 super stamp. This super stamp is centered on the open clusters M35 and NGC2158. Approximately 46% of our periodic variables were previously unreported. Of the catalog variables, we find that 331 are members of M35 and 56 are members of NGC 2158 (P_m_>0.5). Our catalog contains two new transiting exoplanet candidates, both of which orbit field stars. The smaller planet candidate has a radius of 0.35+/-0.04R_J_ and orbits a K dwarf (Kp=15.4mag) with a transit depth of 2.9mmag. The larger planet candidate has a radius of 0.72+/-0.02R_J_ and orbits a late G-type star (Kp=15.7mag) with a transit depth of 2.2mmag. The larger planet candidate may be an unresolved binary or a false alarm. Our catalog includes 44 eclipsing binaries (EBs), including ten new detections. Of the EBs, one is an M35 member and five are NGC 2158 members. Our catalog contains a total of 1097 nontransiting variable stars, including a field {delta} Cepheid exhibiting double mode pulsations, 561 rotational variables, and 251 pulsating variables (primarily {gamma} Doradus and {delta} Scuti types). The periods of our catalog sources range between 43 minutes to 24 days. The known ages of our reported cluster variables will facilitate investigations of a variety of stellar evolutionary processes.
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- ID:
- ivo://CDS.VizieR/J/ApJS/222/19
- Title:
- KPNO spectroscopy of G & K dwarfs HIP stars
- Short Name:
- J/ApJS/222/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tension between the Hipparcos parallax of the Pleiades and other independent distance estimates continues even after the new reduction of the Hipparcos astrometric data and the development of a new geometric distance measurement for the cluster. A short Pleiades distance from the Hipparcos parallax predicts a number of stars in the solar neighborhood that are sub-luminous at a given photospheric abundance. We test this hypothesis using the spectroscopic abundances for a subset of stars in the Hipparcos catalog, which occupy the same region as the Pleiades in the color-magnitude diagram. We derive stellar parameters for 170 nearby G- and K-type field dwarfs in the Hipparcos catalog based on high-resolution spectra obtained using KPNO 4m echelle spectrograph. Our analysis shows that, when the Hipparcos parallaxes are adopted, most of our sample stars follow empirical color-magnitude relations. A small fraction of stars are too faint compared to main-sequence fitting relations by {Delta}M_V_>~0.3mag, but the differences are marginal at a 2{sigma} level, partly due to relatively large parallax errors. On the other hand, we find that the photometric distances of stars showing signatures of youth as determined from lithium absorption line strengths and R'_HK_ chromospheric activity indices are consistent with the Hipparcos parallaxes. Our result is contradictory to a suggestion that the Pleiades distance from main-sequence fitting is significantly altered by stellar activity and/or the young age of its stars, and provides an additional supporting evidence for the long-distance scale of the Pleiades.
- ID:
- ivo://CDS.VizieR/J/AJ/133/768
- Title:
- KPNO's UBVRI filter transmission characteristics
- Short Name:
- J/AJ/133/768
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric data on the Johnson-Kron-Cousins UBVRI broadband photometric system are provided for a set of stars that have been used as spectrophotometric standard stars for the Hubble Space Telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/528/123
- Title:
- KRI photometry of galaxies near B2 1335+28
- Short Name:
- J/ApJ/528/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We previously reported a significant clustering of red galaxies (R-K=3.56) around the radio-loud quasar B2 1335+28 at z=1.086. In this paper, we establish the existence of a rich cluster at the quasar redshift and study the properties of the cluster galaxies through further detailed analysis of the photometric data. We also list the positions, K-band magnitudes, and colors of all K<19 objects. The near-infrared (NIR) K-band imaging data presented in earlier paper, together with some additional K-band data, is newly analyzed to study the extent of the clustering of the red galaxies. We also constrain the cluster redshift by applying a robust photometric redshift estimator and find a strong peak around z=1.1. The color distribution of the galaxies in the cluster is quite broad, and the fraction of blue galaxies (70%) is much larger than in intermediate-redshift clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/879/100
- Title:
- K2 rotation periods for Hyades & Praesepe members
- Short Name:
- J/ApJ/879/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze K2 light curves for 132 low-mass (1M_{sun}_>~M*>~0.1M_{sun}_) members of the 600-800Myr old Hyades cluster and measure rotation periods (P_rot_) for 116 of these stars. These include 93 stars with no prior P_rot_ measurements; the total number of Hyads with a known P_rot_ is now 232. We then combine literature binary data with Gaia DR2 photometry and astrometry to select single-star sequences in the Hyades and its roughly coeval Praesepe open cluster and derive a new reddening value of A_V_=0.035+/-0.011 for Praesepe. Comparing the effective temperature-P_rot_ distributions for the Hyades and Praesepe, we find that solar-type Hyads rotate, on average, 0.4d slower than their Praesepe counterparts. This P_rot_ difference indicates that the Hyades is slightly older than Praesepe: we apply a new gyrochronology model tuned with Praesepe and the Sun and find an age difference between the two clusters of 57Myr. However, this P_rot_ difference decreases and eventually disappears for lower-mass stars. This provides further evidence for stalling in the rotational evolution of these stars and highlights the need for more detailed analysis of angular momentum evolution for stars of different masses and ages.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/22
- Title:
- Ks absolute magnitudes from LAMOST for OB stars
- Short Name:
- J/ApJS/253/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a data-driven method to estimate absolute magnitudes for O- and B-type stars from the LAMOST spectra, which we combine with Gaia DR2 parallaxes to infer distance and binarity. The method applies a neural network model trained on stars with precise Gaia parallax to the spectra and predicts K_s_-band absolute magnitudes M_Ks_ with a precision of 0.25mag, which corresponds to a precision of 12% in spectroscopic distance. For distant stars (e.g., >5kpc), the inclusion of constraints from spectroscopic M_Ks_ significantly improves the distance estimates compared to inferences from Gaia parallax alone. Our method accommodates for emission-line stars by first identifying them via principal component analysis reconstructions and then treating them separately for the M_Ks_ estimation. We also take into account unresolved binary/multiple stars, which we identify through deviations in the spectroscopic M_Ks_ from the geometric M_Ks_ inferred from Gaia parallax. This method of binary identification is particularly efficient for unresolved binaries with near equal-mass components and thus provides a useful supplementary way to identify unresolved binary or multiple-star systems. We present a catalog of spectroscopic M_Ks_, extinction, distance, flags for emission lines, and binary classification for 16002 OB stars from LAMOST DR5. As an illustration, we investigate the M_Ks_ of the enigmatic LB-1 system, which Liu et al. 2019Natur.575..618L had argued consists of a B star and a massive stellar-mass black hole. Our results suggest that LB-1 is a binary system that contains two luminous stars with comparable brightness, and the result is further supported by parallax from the Gaia eDR3.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/28
- Title:
- K2 star parameters from Gaia & LAMOST
- Short Name:
- J/ApJS/247/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous measurements of stellar properties for K2 stars in the Ecliptic Plane Input Catalog (EPIC) largely relied on photometry and proper motion measurements, with some added information from available spectra and parallaxes. Combining Gaia DR2 distances with spectroscopic measurements of effective temperatures, surface gravities, and metallicities from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we computed updated stellar radii and masses for 26838 K2 stars. For 195250 targets without a LAMOST spectrum, we derived stellar parameters using random forest regression on photometric colors trained on the LAMOST sample. In total, we measured spectral types, effective temperatures, surface gravities, metallicities, radii, and masses for 222088 A, F, G, K, and M-type K2 stars. With these new stellar radii, we performed a simple reanalysis of 299 confirmed and 517 candidate K2 planet radii from Campaigns 1-13, elucidating a distinct planet radius valley around 1.9R_{Earth}_, a feature thus far only conclusively identified with Kepler planets, and tentatively identified with K2 planets. These updated stellar parameters are a crucial step in the process toward computing K2 planet occurrence rates.
- ID:
- ivo://CDS.VizieR/J/AJ/160/209
- Title:
- K2 & TESS Synergy. I. Parameters & LC, 4 stars
- Short Name:
- J/AJ/160/209
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although the Transiting Exoplanet Survey Satellite (TESS) primary mission observed the northern and southern ecliptic hemispheres, generally avoiding the ecliptic, and the Kepler space telescope during the K2 mission could only observe near the ecliptic, many of the K2 fields extend far enough from the ecliptic plane that sections overlap with TESS fields. Using photometric observations from both K2 and TESS, combined with archival spectroscopic observations, we globally modeled four known planetary systems discovered by K2 that were observed in the first year of the primary TESS mission. Specifically, we provide updated ephemerides and system parameters for K2-114b, K2-167b, K2-237b, and K2-261b. These were some of the first K2 planets to be observed by TESS in the first year and include three Jovian sized planets and a sub-Neptune with orbital periods less than 12 days. In each case, the updated ephemeris significantly reduces the uncertainty in prediction of future times of transit, which is valuable for planning observations with the James Webb Space Telescope and other future facilities. The TESS extended mission is expected to observe about half of the K2 fields, providing the opportunity to perform this type of analysis on a larger number of systems.
- ID:
- ivo://CDS.VizieR/J/AJ/162/101
- Title:
- K2 ugri & H{alpha} photometry in the Lagoon Nebula
- Short Name:
- J/AJ/162/101
- Date:
- 14 Mar 2022 06:42:13
- Publisher:
- CDS
- Description:
- Space observatories have provided unprecedented depictions of the many variability behaviors typical of low-mass, young stars. However, those studies have so far largely omitted more massive objects (~2M{sun} to 4-5M{sun}) and were limited by the absence of simultaneous, multiwavelength information. We present a new study of young star variability in the ~1-2Myr old, massive Lagoon Nebula region. Our sample encompasses 278 young, late B to K-type stars, monitored with Kepler/K2. Auxiliary u, g, r, i, H{alpha} time-series photometry, simultaneous with K2, was acquired at the Paranal Observatory. We employed this comprehensive data set and archival infrared photometry to determine individual stellar parameters, assess the presence of circumstellar disks, and tie the variability behaviors to inner disk dynamics. We found significant mass-dependent trends in variability properties, with B/A stars displaying substantially reduced levels of variability compared to G/K stars for any light-curve morphology. These properties suggest different magnetic field structures at the surface of early-type and later-type stars. We also detected a dearth of some disk-driven variability behaviors, particularly dippers, among stars earlier than G. This indicates that their higher surface temperatures and more chaotic magnetic fields prevent the formation and survival of inner disk dust structures corotating with the star. Finally, we examined the characteristic variability timescales within each light curve and determined that the day-to-week timescales are predominant over the K2 time series. These reflect distinct processes and locations in the inner disk environment, from intense accretion triggered by instabilities in the innermost disk regions to variable accretion efficiency in the outer magnetosphere.
- ID:
- ivo://CDS.VizieR/J/ApJS/234/5
- Title:
- LaCoSSPAr in the Southern Galactic Cap. I.
- Short Name:
- J/ApJS/234/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic redshift catalog from the LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap (SGC), which is designed to observe all sources (Galactic and extragalactic) by using repeating observations with a limiting magnitude of r=18.1mag in two 20deg^2^ fields. The project is mainly focusing on the completeness of LAMOST ExtraGAlactic Surveys (LEGAS) in the SGC, the deficiencies of source selection methods, and the basic performance parameters of the LAMOST telescope. In both fields, more than 95% of galaxies have been observed. A post-processing has been applied to the LAMOST 1D spectrum to remove the majority of remaining sky background residuals. More than 10000 spectra have been visually inspected to measure the redshift by using combinations of different emission/absorption features with an uncertainty of {sigma}_z_/(1+z)<0.001. In total, 1528 redshifts (623 absorption and 905 emission line galaxies) in Field A and 1570 redshifts (569 absorption and 1001 emission line galaxies) in Field B have been measured. The results show that it is possible to derive redshift from low S/N galaxies with our post-processing and visual inspection. Our analysis also indicates that up to one-fourth of the input targets for a typical extragalactic spectroscopic survey might be unreliable. The multi-wavelength data analysis shows that the majority of mid-infrared-detected absorption (91.3%) and emission line galaxies (93.3%) can be well separated by an empirical criterion of W2-W3=2.4. Meanwhile, a fainter sequence paralleled to the main population of galaxies has been witnessed both in Mr/W2-W3 and M*/W2-W3 diagrams, which could be the population of luminous dwarf galaxies but contaminated by the edge-on/highly inclined galaxies (~30%).
