- ID:
- ivo://CDS.VizieR/J/ApJ/871/63
- Title:
- How to constrain your M dwarf. II. Nearby binaries
- Short Name:
- J/ApJ/871/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass-luminosity relation for late-type stars has long been a critical tool for estimating stellar masses. However, there is growing need for both a higher-precision relation and a better understanding of systematic effects (e.g., metallicity). Here we present an empirical relationship between M_Ks_ and M_*_ spanning 0.075M_{sun}_<M_*_<0.70M_{sun}_. The relation is derived from 62 nearby binaries, whose orbits we determine using a combination of near infra-red (Keck/NIRC2) imaging, archival adaptive optics data, and literature astrometry. From their orbital parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use these total masses, in combination with resolved Ks magnitudes and system parallaxes, to calibrate the M_Ks_-M_*_ relation. The resulting posteriors can be used to determine masses of single stars with a precision of 2%-3%, which we confirm by testing the relation on stars with individual dynamical masses from the literature. The precision is limited by scatter around the best-fit relation beyond measured M_*_ uncertainties, perhaps driven by intrinsic variation in the M_Ks_-M_*_ relation or underestimated uncertainties in the input parallaxes. We find that the effect of [Fe/H] on the M_Ks_-M_*_ relation is likely negligible for metallicities in the solar neighborhood (0.0%{+/-}2.2% change in mass per dex change in [Fe/H]). This weak effect is consistent with predictions from the Dartmouth Stellar Evolution Database, but inconsistent with those from modules for experiments in stellar astrophysics (MESA) Isochrones and Stellar Tracks (MIST) (at 5{sigma}). A sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in extreme populations (e.g., in the Galactic halo or thick disk).
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/738/186
- Title:
- HST and DEIMOS measurements of NGC 2419 stars
- Short Name:
- J/ApJ/738/186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of a kinematic data set of stars in the globular cluster NGC 2419, taken with the DEep Imaging Multi-Object Spectrograph at the Keck II telescope. Combined with a reanalysis of deep Hubble Space Telescope and Subaru Telescope imaging data, which provide an accurate luminosity profile of the cluster, we investigate the validity of a large set of dynamical models of the system, which are checked for stability via N-body simulations.
- ID:
- ivo://CDS.VizieR/J/ApJ/900/183
- Title:
- HST NIR grism sp. of strong-lensing galaxy clusters
- Short Name:
- J/ApJ/900/183
- Date:
- 15 Feb 2022 11:31:32
- Publisher:
- CDS
- Description:
- We present the hitherto largest sample of gas-phase metallicity radial gradients measured at sub-kpc resolution in star-forming galaxies in the redshift range of 1.2<z<=2.3. These measurements are enabled by the synergy of slitless spectroscopy from the Hubble Space Telescope near-infrared channels and the lensing magnification from foreground galaxy clusters. Our sample consists of 76 galaxies with stellar mass ranging from 10^7^ to 10^10^M_{sun}, an instantaneous star formation rate in the range of [1,100]M_{sun}_/yr, and global metallicity [1/12,2] of solar. At a 2{sigma} confidence level, 15/76 galaxies in our sample show negative radial gradients, whereas 7/76 show inverted gradients. Combining ours and all other metallicity gradients obtained at a similar resolution currently available in the literature, we measure a negative mass dependence of {Delta}log(O/H)/{Delta}r[dex/kpc]=(-0.020+/-0.007)+(-0.016+/-0.008) log(M_*_/10^9.4^M_{sun}_), with the intrinsic scatter being {sigma}=0.060+/-0.006 over 4 orders of magnitude in stellar mass. Our result is consistent with strong feedback, not secular processes, being the primary governor of the chemostructural evolution of star-forming galaxies during the disk mass assembly at cosmic noon. We also find that the intrinsic scatter of metallicity gradients increases with decreasing stellar mass and increasing specific star formation rate. This increase in the intrinsic scatter is likely caused by the combined effect of cold-mode gas accretion and merger-induced starbursts, with the latter more predominant in the dwarf mass regime of M_*_<~10^9^M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/777/79
- Title:
- HST photometry of Cepheid candidates in M101
- Short Name:
- J/ApJ/777/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The impact of metallicity on the Cepheid period-luminosity (P-L) relation is investigated using Hubble Space Telescope Advanced Camera for Surveys V and I images of M101. Variations in the reddening-free Wesenheit parameter (W), which is employed as a proxy for luminosity, are examined as a function of the radial distance from the center of M101 (and thus metallicity). We determine that there is no dependence of the slope on metallicity. However, the intercept is found to depend on metallicity by {gamma}_VI_=-0.33+/-0.12mag.dex^-1^ and {gamma}_VI_=-0.71+/-0.17mag.dex^-1^ using 2{sigma} and 3{sigma} rejection criteria, respectively. Sigma-clipping impacts the derived metallicity dependence, and the 2{sigma} criterion applied likely mitigates blending, particularly in the crowded inner regions of M101. A metallicity-corrected distance for M101 is obtained from 619 Cepheids ({mu}=28.96+/-0.11), a result that agrees with the recently determined SN Ia distance. The metallicity effects described can be bypassed by working at near and mid-infrared wavelengths (e.g., the Carnegie Hubble Program).
- ID:
- ivo://CDS.VizieR/J/A+A/391/945
- Title:
- HST photometry of 74 galactic globular clusters
- Short Name:
- J/A+A/391/945
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the complete photometric database and the color-magnitude diagrams for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the F439W and F555W bands. A detailed discussion of the various reduction steps is also presented, and of the procedures to transform instrumental magnitudes into both the HST F439W and F555W flight system and the standard Johnson B and V systems. We also describe the artificial star experiments which have been performed to derive the star count completeness in all the relevant branches of the color magnitude diagram. The entire photometric database and the completeness function will be made available on the Web immediately after the publication of the present paper.
- ID:
- ivo://CDS.VizieR/J/ApJ/827/12
- Title:
- HSTPROMO catalogs of GCs. IV. Blue straggler stars
- Short Name:
- J/ApJ/827/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We make use of the Hubble Space Telescope proper-motion catalogs derived by Bellini et al. (Paper I, 2014, J/ApJ/797/115) to produce the first radial velocity dispersion profiles {sigma}(R) for blue straggler stars (BSSs) in Galactic globular clusters (GCs), as well as the first dynamical estimates for the average mass of the entire BSS population. We show that BSSs typically have lower velocity dispersions than stars with mass equal to the main-sequence turnoff mass, as one would expect for a more massive population of stars. Since GCs are expected to experience some degree of energy equipartition, we use the relation {sigma}{propto}M^-{eta}^, where {eta} is related to the degree of energy equipartition, along with our velocity dispersion profiles to estimate BSS masses. We estimate {eta} as a function of cluster relaxation from recent Monte Carlo cluster simulations by Bianchini+ (2016MNRAS.458.3644B) and then derive an average mass ratio M_BSS_/M_MSTO_=1.50+/-0.14 and an average mass M_BSS_=1.22+/-0.12M_{sun}_ from 598 BSSs across 19 GCs. The final error bars include any systematic errors that are random between different clusters, but not any potential biases inherent to our methodology. Our results are in good agreement with the average mass of M_BSS_=1.22+/-0.06M_{sun}_ for the 35 BSSs in Galactic GCs in the literature with properties that have allowed individual mass determination.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A25
- Title:
- HST WFC3 photometry of NGC 2419
- Short Name:
- J/A+A/624/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new deep imaging of the central regions of the remote globular cluster NGC 2419, obtained with the F343N and F336W filters of the Wide Field Camera 3 on board the Hubble Space Telescope. The new data are combined with archival imaging to constrain nitrogen and helium abundance variations within the cluster. We find a clearly bimodal distribution of the nitrogen-sensitive F336W-F343N colours of red giants, from which we estimate that about 55% of the giants belong to a population with about normal (field-like) nitrogen abundances (P1), while the remaining 45% belong to a nitrogen-rich population (P2). On average, the P2 stars are more He-rich than the P1 stars, with an estimated mean difference of {Delta}Y~=0.05, but the P2 stars exhibit a significant spread in He content and some may reach {Delta}Y~=0.13. A smaller He spread may also be present for the P1 stars. Additionally, stars with spectroscopically determined low Mg abundances ([Mg/Fe]<0) are generally associated with P2. We find the P2 stars to be slightly more centrally concentrated in NGC 2419 with a projected half-number radius of about 10% less than for the P1 stars, but the difference is not highly significant (p~=0.05). Using published radial velocities, we find evidence of rotation for the P1 stars, whereas the results are inconclusive for the P2 stars, which are consistent with no rotation as well as the same average rotation found for the P1 stars. Because of the long relaxation time scale of NGC 2419, the radial trends and kinematic properties of the populations are expected to be relatively unaffected by dynamical evolution. Hence, they provide constraints on formation scenarios for multiple populations, which must account not only for the presence of He spreads within sub-populations identified via CNO variations, but also for the relatively modest differences in the spatial distributions and kinematics of the populations.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/39
- Title:
- Hydra I wide-field imaging and spectroscopy obs.
- Short Name:
- J/ApJ/818/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d~10kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (~5-6Gyr) and metallicity ([Fe/H]=-0.9dex). We measure statistically significant spreads in both the iron and alpha-element abundances of {sigma}_[Fe/H]_=0.13+/-0.02dex and {sigma}_[{alpha}/Fe]_=0.09+/-0.03dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H] --as well as its low [{alpha}/Fe], apparent [Fe/H] spread, and present-day low luminosity-- suggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass.
- ID:
- ivo://CDS.VizieR/J/MNRAS/431/1005
- Title:
- IC 2391 and Argus young stars
- Short Name:
- J/MNRAS/431/1005
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the possible connection between the open cluster IC 2391 and the unbound Argus association identified by the search for associations containing young stars survey. In addition to common kinematics and ages between these two systems, here we explore their chemical abundance patterns to confirm if the two substructures shared a common origin. We carry out a homogeneous high-resolution elemental abundance study of eight confirmed members of IC 2391 as well as six members of the Argus association using UVES spectra. We derive spectroscopic stellar parameters and abundances for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba. All stars in the open cluster and Argus association were found to share similar abundances with the scatter well within the uncertainties, where [Fe/H]=-0.04+/-0.03 for cluster stars and [Fe/H]=-0.06+/-0.05 for Argus stars. Effects of overionization/excitation were seen for stars cooler than roughly 5200K as previously noted in the literature. Also, enhanced Ba abundances of around 0.6dex were observed in both systems. The common ages, kinematics and chemical abundances strongly support the fact that the Argus association stars originated from the open cluster IC 2391. Simple modelling of this system finds this dissolution to be consistent with two-body interactions.
- ID:
- ivo://CDS.VizieR/J/A+A/556/A121
- Title:
- Identification of metal-poor stars with ANN
- Short Name:
- J/A+A/556/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Identification of metal-poor stars among field stars is extremely useful for studying the structure and evolution of the Galaxy and of external galaxies. We search for metal-poor stars using the artificial neural network (ANN) and extend its usage to determine absolute magnitudes. We have constructed a library of 167 medium-resolution stellar spectra (R~1200) covering the stellar temperature range of 4200 to 8000K, logg range of 0.5 to 5.0, and [Fe/H] range of -3.0 to dex. This empirical spectral library was used to train ANNs, yielding an accuracy of 0.3dex in [Fe/H], 200K in temperature, and 0.3dex in logg. We found that the independent calibrations of near-solar metallicity stars and metal-poor stars decreases the errors in Teff and logg by nearly a factor of two.
