- ID:
- ivo://CDS.VizieR/J/ApJ/689/1295
- Title:
- Lithium test implications for brown dwarfs
- Short Name:
- J/ApJ/689/1295
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a large sample of optical spectra of late-type dwarfs, we identify a subset of late-M through L field dwarfs that, because of the presence of low-gravity features in their spectra, are believed to be unusually young. From a combined sample of 303 field L dwarfs, we find observationally that 7.6+/-1.6% are younger than 100Myr. This percentage is in agreement with theoretical predictions once observing biases are taken into account. We find that these young L dwarfs tend to fall in the southern hemisphere (DEC<0{deg}) and may be previously unrecognized, low-mass members of nearby, young associations like Tucana-Horologium, TW Hydrae, {beta} Pictoris, and AB Doradus. We use a homogeneously observed sample of ~150 optical spectra to examine lithium strength as a function of L/T spectral type and further corroborate the trends noted by Kirkpatrick and coworkers. We use our low-gravity spectra to investigate lithium strength as a function of age. The data weakly suggest that for early- to mid-L dwarfs the line strength reaches a maximum for a fewx100Myr, whereas for much older (few Gyr) and much younger (<100Myr) L dwarfs the line is weaker or undetectable.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/128/1233
- Title:
- LkH{alpha} 101 and the young cluster in NGC 1579
- Short Name:
- J/AJ/128/1233
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The central region of the dark cloud L1482 is illuminated by LkH{alpha} 101, a heavily reddened (A_V_~10mag) high-luminosity (>=8x10^3^L_Sun_) star having an unusual emission-line spectrum plus a featureless continuum. About 35 much fainter (mostly between R=16 and >21) H{alpha} emitters have been found in the cloud. Their color-magnitude distribution suggests a median age of about 0.5Myr, with considerable dispersion. There are also at least five bright B-type stars in the cloud, presumably of about the same age; none show the peculiarities expected of HAeBe stars. Dereddened, their apparent V magnitudes lead to a distance of about 700pc. Radio observations suggest that the optical object LkH{alpha} 101 is in fact a hot star surrounded by a small H II region, both inside an optically thick dust shell.
- ID:
- ivo://CDS.VizieR/J/AJ/158/104
- Title:
- LL Com BVR bands photometry & times of light minimum
- Short Name:
- J/AJ/158/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite the discovery of LL Com, a Lyrae-type eclipsing binary system, approximately 60 yr ago, little has been found concerning its detailed photometry and orbital-period change until now. In this paper, we present the first multi-band charge-coupled-device photometric light curves, from which a significant luminosity reduction around the primary eclipse is revealed. Based on LAMOST data, we first determined LL Com's spectrum as F1V and then analyzed the light curves with the 2015 version of the Wilson-Devinney code. The fact that LL Com is a near-contact binary system with a semi-detached configuration, where the secondary component only fills its Roche lobe and the primary component fills more than 95% of its Roche lobe, is suggested through the photometric solution. In addition, according to archival photometry and previously published times of minima, a secular period increase at a rate of P=2.62x10^-7^ day/yr was found, which implies a continuous mass transfer from the secondary to the primary. Utilizing the photometric solution and the simulations of single-particle trajectories, we propose the existence of a cool spot on the surface of the primary component. This cool spot can be naturally produced by the impacts that occur during mass flow, and it also successfully interprets the luminosity reduction in the light curves. Finally, with the combination of thermal relaxation oscillation theory and the Roche-Lobe model, we conclude that LL Com is transitioning from the semi-detached to the detached phase.
- ID:
- ivo://CDS.VizieR/J/A+A/433/117
- Title:
- L- & M-band imaging of the Galactic Center
- Short Name:
- J/A+A/433/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometric data of the sources detected in NAOS/CONICA H- and K-band (1.6 and 2.1{mu}m) and ISAAC L- and M-band (3.8 and 4.7{mu}m) images of the Galactic Center, obtained in May and August 2002, are presented. For each source, name (if relevant), position offset, H-, K-, L- and M-band magnitude (if available) and observed colors (H-K, K-L and L-M) are given. The position zero-point is RA = 17:45:40.26, DE = -29:00:29.91 (IRS 16NE) in the J2000 system, with an offset of 2.83" (RA) and -0.91" (DE) from Sgr A*. The total photometric accuracy is +/-0.25mag in H- and K-band, +/-0.15mag in L- and M-band, positional accuracy is +/-0.09".
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/2307
- Title:
- LMC anomalous Cepheid Ks light curves
- Short Name:
- J/MNRAS/437/2307
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The VISTA near-infrared YJKs survey of the Magellanic Clouds System (VMC, PI M.-R. L. Cioni) is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we present for the first time Ks-band light curves for anomalous Cepheid (AC) variables. In particular, we have analysed a sample of 48 Large Magellanic Cloud ACs, for which identification and optical magnitudes were obtained from the OGLE III and IV catalogues. The VMC Ks-band light curves for ACs are well sampled, with the number of epochs ranging from 8 to 16, and allowing us to obtain very precise mean Ks magnitudes with errors on average of the order of 0.01mag. The <Ks> values were used to build the first period-luminosity and period-Wesenheit relations in the near-infrared for fundamental mode and first overtone ACs. At the same time we exploited the optical (V, I) OGLE data to build accurate period-luminosity, period-luminosity-colour and period-Wesenheit relations both for fundamental mode and first overtone ACs. For the first time, these relations were derived from a sample of pulsators which uniformly cover the whole AC instability strip. The application of the optical period-Wesenheit relation to a sample of dwarf galaxies hosting a significant population of ACs revealed that this relation is a valuable tool for deriving distances within the Local Group. Due to its lower dispersion, we expect the Ks period-Wesenheit relations first derived in this paper to represent a valuable tool for measuring accurate distances to galaxies hosting ACs when more data in near-infrared filters become available.
- ID:
- ivo://CDS.VizieR/J/AJ/154/102
- Title:
- LMC blue supergiants spectroscopic observations
- Short Name:
- J/AJ/154/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-quality spectra of 90 blue supergiant stars in the Large Magellanic Cloud are analyzed with respect to effective temperature, gravity, metallicity, reddening, extinction, and extinction law. An average metallicity, based on Fe and Mg abundances, relative to the Sun of [Z]=-0.35+/-0.09 dex is obtained. The reddening distribution peaks at E(B-V)=0.08 mag, but significantly larger values are also encountered. A wide distribution of the ratio of extinction to reddening is found ranging from R_V_=2 to 6. The results are used to investigate the blue supergiant relationship between flux-weighted gravity, g_F_=g/T_eff_^4^, and absolute bolometric magnitude M_bol_. The existence of a tight relationship, the Flux-weighted Gravity-Luminosity Relationship (FGLR), is confirmed. However, in contrast to previous work, the observations reveal that the FGLR is divided into two parts with a different slope. For flux-weighted gravities larger than 1.30 dex, the slope is similar to that found in previous work, but the relationship becomes significantly steeper for smaller values of the flux-weighted gravity. A new calibration of the FGLR for extragalactic distance determinations is provided.
- ID:
- ivo://CDS.VizieR/J/AJ/124/2039
- Title:
- LMC Blue variable stars from MACHO
- Short Name:
- J/AJ/124/2039
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the photometric properties of 1280 blue variable stars within the Large Megallanic Cloud. Photometry is derived from the MACHO database. The light curves of the sample exhibit a variety of quasi-periodic and aperiodic outburst behavior. A characteristic feature of the photometric variation is that the objects are reddest when at maximum outburst. A subset of 102 objects were examined spectroscopically. Within this subset, 91% exhibited Balmer emission in at least one epoch, in some cases with spectacular spectral variability. The variability observed in the sample is consistent with the establishment and maintenance of the Be phenomenon.
- ID:
- ivo://CDS.VizieR/J/AJ/149/117
- Title:
- LMC infrared survey. I. Photometry of Cepheids
- Short Name:
- J/AJ/149/117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observational details and first results of a near-infrared (JHK_s_) synoptic survey of the central region of the Large Magellanic Cloud (LMC) using the CPAPIR camera at the CTIO 1.5m telescope. We covered 18 square degrees to a depth of K_s_~16.5mag and obtained an average of 16 epochs in each band at any given location. Our catalog contains more than 3.5x10^6^ sources, including 1417 Cepheid variables previously studied at optical wavelengths by the OGLE survey. Our sample of fundamental-mode pulsators represents a nine-fold increase in the number of these variables with time-resolved, multi-band near-infrared photometry. We combine our large Cepheid sample and a recent precise determination of the distance to the LMC to derive a robust absolute calibration of the near-infrared Leavitt Law for fundamental-mode and first-overtone Cepheids with 10x better constraints on the slopes relative to previous work. We also obtain calibrations for the tip of the red giant branch and the red clump based on our ensemble photometry which are in good agreement with previous determinations.
- ID:
- ivo://CDS.VizieR/J/AJ/153/154
- Title:
- LMC NIR survey. IV. Type II Cepheid variables
- Short Name:
- J/AJ/153/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present time-series observations of Population II Cepheids in the Large Magellanic Cloud at near-infrared (JHK_s_) wavelengths. Our sample consists of 81 variables with accurate periods and optical (VI) magnitudes from the OGLE survey, covering various subtypes of pulsators (BL Herculis, W Virginis, and RV Tauri). We generate light-curve templates using high-quality I-band data in the LMC from OGLE and K_s_-band data in the Galactic bulge from VISTA Variables in Via Lactea survey (2010NewA...15..433M) and use them to obtain robust mean magnitudes. We derive period-luminosity (P-L) relations in the near-infrared and Period-Wesenheit (P-W) relations by combining optical and near-infrared data. Our P-L and P-W relations are consistent with published work when excluding long-period RV Tauris. We find that Pop II Cepheids and RR Lyraes follow the same P-L relations in the LMC. Therefore, we use trigonometric parallax from the Gaia DR1 (Cat. I/337) for VY Pyx and the Hubble Space Telescope parallaxes for k Pav and 5 RR Lyrae variables to obtain an absolute calibration of the Galactic K_s_-band P-L relation, resulting in a distance modulus to the LMC of {mu}_LMC_=18.54+/-0.08 mag. We update the mean magnitudes of Pop II Cepheids in Galactic globular clusters using our light-curve templates and obtain distance estimates to those systems, anchored to a precise late-type eclipsing binary distance to the LMC. We find that the distances to these globular clusters based on Pop II Cepheids are consistent (within 2{sigma}) with estimates based on the M_V_-[Fe/H] relation for horizontal branch stars.
- ID:
- ivo://CDS.VizieR/J/AJ/151/88
- Title:
- LMC NIR Synoptic Survey. II. Wesenheit relations
- Short Name:
- J/AJ/151/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new near-infrared (NIR) Cepheid period-Wesenheit (P-W) relations in the LMC using time-series observations from the Large Magellanic Cloud NIR Synoptic Survey. We also derive optical+NIR P-W relations using V and I magnitudes from the Optical Gravitational Lensing Experiment. We employ our new JHK_s_ data to determine an independent distance to the LMC of {mu}_LMC_=18.47+/-0.07 (statistical) mag, using an absolute calibration of the Galactic relations based on several distance determination methods and accounting for the intrinsic scatter of each technique. We also derive new NIR period-luminosity and Wesenheit relations for Cepheids in M31 using observations from the Panchromatic Hubble Andromeda Treasury survey. We use the absolute calibrations of the Galactic and LMC W_J,H_ relations to determine the distance modulus of M31, {mu}_M31_=24.46+/-0.20 mag. We apply a simultaneous fit to Cepheids in several Local Group galaxies covering a range of metallicities (7.7<12+log[O/H]<8.6 dex) to determine a global slope of -3.244+/-0.016 mag/dex for the W_J,H_ relation and obtain robust distance estimates. Our distances are in good agreement with recent TRGB based distance estimates and we do not find any evidence for a metallicity dependence in the NIR P-W relations.
