- ID:
- ivo://CDS.VizieR/J/other/AstBu/72.51
- Title:
- LAMOST stars radii, masses, luminosities
- Short Name:
- J/other/AstBu/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the spectral observations of the LAMOST (DR2) survey, the radii, masses, and luminosities of 700480 stars were estimated. These stars belong to spectral types A, F, G, and K, and have metallicities between -0.845 and 0.0. To determine the properties of the stars, we used up-to-date modelsof the stellar interior structure, computed with account for the stellar evolution rate and the initial mass function. The use of evolutionary estimates for two types of stars - with and without rotation - allowed us to account for the uncertainty associated with the lack of data on the rotation velocity of the stars under consideration. The obtained stellar radii, together with the photometric estimates of interstellar extinction and angular diameters can be used to study the dependence of interstellar extinction on distance as well as to estimate the stellar distances.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/152/45
- Title:
- LAMOST survey of star clusters in M31. II.
- Short Name:
- J/AJ/152/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We select from Paper I a sample of 306 massive star clusters observed with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) in the vicinity fields of M31 and M33, and determine their metallicities, ages, and masses. Metallicities and ages are estimated by fitting the observed integrated spectra with stellar synthesis population (SSP) models with a pixel-to-pixel spectral fitting technique. Ages for most young clusters are also derived by fitting the multi-band photometric measurements with model spectral energy distributions (SEDs). The estimated cluster ages span a wide range, from several million years to the age of the universe. The numbers of clusters younger and older than 1Gyr are, respectively, 46 and 260. With ages and metallicities determined, cluster masses are then estimated by comparing the multi-band photometric measurements with SSP model SEDs. The derived masses range from ~10^3^ to ~10^7^M_{Sun}_, peaking at ~10^4.3^ and ~10^5.7^M_{Sun}_ for young (<1Gyr) and old (>1Gyr) clusters, respectively. Our estimated metallicities, ages, and masses are in good agreement with available literature values. Old clusters richer than [Fe/H]~-0.7dex have a wide range of ages. Those poorer than [Fe/H]~-0.7dex seem to be composed of two groups, as previously found for Galactic globular clusters-one of the oldest ages with all values of metallicity down to ~-2dex and another with metallicity increasing with decreasing age. The old clusters in the inner disk of M31 (0-30kpc) show a clear metallicity gradient measured at -0.038+/-0.023dex/kpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/716/993
- Title:
- LAMP: reverberation mapping of H and He lines
- Short Name:
- J/ApJ/716/993
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z<0.05) Seyfert 1 galaxies with expected masses in the range ~10^6^-10^7^M_{sun}_ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad H{beta} emission, which we have previously reported. We present here the light curves for the H{alpha}, H{gamma}, HeII{lambda}4686, and HeI{lambda}5876 emission lines and the time lags for the emission-line responses relative to changes in the continuum flux.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A8
- Title:
- L1448 and HH211 CO(6-5) velocity maps
- Short Name:
- J/A+A/555/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of CO rotational transitions in the 0.3-0.4 millimeter range, now possible from exceptional sites on the ground, provide the opportunity of studing the warm component of molecular outflows in star-forming regions. This study aims to characterize the role of the warm gas in high-velocity and collimated outflows from Class 0 low-mass protostars. We used the CHAMP+ heterodyne array on the APEX telescope to map the CO (6-5) and CO (7-6) emission in the well-known Class 0 outflows L1448-mm and HH211-mm. We complement these data with ^13^CO (6-5) observations and also with previous low-J CO observations. The CO (6-5) and (7-6) emission was detected to be tracing the outflow lobes. In L1448, extremely high-velocity (EHV) emission was detected in both transitions. In HH211, high-velocity CO (6-5) emission was detected to be tracing the regions close to the central object, but it was also found close to the bow-shock regions seen in the mid-IR. A large velocity gradient code applied to these and the complementary low-J CO data revealed the high-velocity components to be dense (10^5^cm^-3) and warm (T>200K) gas, in agreement with previous observations of shock tracers such as SiO. The high-velocity emission of these mid-J CO transitions are very good tracers of the inner highly excited part of outflows, which possibly is molecular material related to the underlying jet. In addition, these transitions are also strong at the bow-shock positions, which make them a good tool for probing these environments.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A142
- Title:
- L1544 1.2 and 2mm emission maps
- Short Name:
- J/A+A/606/A142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In dense and cold molecular clouds dust grains are surrounded by thick icy mantles. It is however not clear if dust growth and coagulation take place before the switch-on of a protostar. This is an important issue, as the presence of large grains may affect the chemical structure of dense cloud cores, including the dynamically important ionization fraction, and the future evolution of solids in protoplanetary disks. To study this further, we focus on L1544, one of the most centrally concentrated pre-stellar cores on the verge of star formation, and with a well-known physical structure. We observed L1544 at 1.2 and 2mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used data from the Herschel Space Observatory archive. We find no evidence of grain growth towards the center of L1544 at the available angular resolution. Therefore, we conclude that single dish observations do not allow us to investigate grain growth towards the pre-stellar core L1544 and high sensitivity interferometer observations are needed. We predict that dust grains can grow to 200um in size toward the central ~300au of L1544. This will imply a dust opacity change by a factor of ~2.5 at 1.2mm, which can be detected using the Atacama Large Millimeter and submillimeter Array (ALMA) at different wavelengths and with an angular resolution of 2".
- ID:
- ivo://svo.cab/cat/chiu06
- Title:
- L and T dwarf (Chiu et al. 2006)
- Short Name:
- Chiu2006
- Date:
- 03 Jun 2020 15:34:07
- Publisher:
- SVO/CAB
- Description:
- L and T dwarf (Chiu et al. 2006)
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/3651
- Title:
- L and T dwarfs from UKIDSS LAS
- Short Name:
- J/MNRAS/449/3651
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the spectroscopic analysis of a large sample of late-M, L, and T dwarfs from the United Kingdom Deep Infrared Sky Survey. Using the YJHK photometry from the Large Area Survey and the red-optical photometry from the Sloan Digital Sky Survey we selected a sample of 262 brown dwarf candidates and we have followed-up 196 of them using the echelle spectrograph X-shooter on the Very Large Telescope. The large wavelength coverage (0.30-2.48um) and moderate resolution (R~5000-9000) of X-shooter allowed us to identify peculiar objects including 22 blue L dwarfs, 2 blue T dwarfs, and 2 low-gravity M dwarfs. Using a spectral indices-based technique, we identified 27 unresolved binary candidates, for which we have determined the spectral type of the potential components via spectral deconvolution. The spectra allowed us to measure the equivalent width of the prominent absorption features and to compare them to atmospheric models. Cross-correlating the spectra with a radial velocity standard, we measured the radial velocity of our targets, and we determined the distribution of the sample, which is centred at -1.7+/-1.2km/s with a dispersion of 31.5km/s. Using our results, we estimated the space density of field brown dwarfs and compared it with the results of numerical simulations. Depending on the binary fraction, we found that there are (0.85+/-0.55)x10^-3^ to (1.00+/-0.64)x10^-3^ objects per cubic parsec in the L4-L6.5 range, (0.73+/-0.47)x10^-3^ to (0.85+/-0.55)x10^-3^ objects per cubic parsec in the L7-T0.5 range, and (0.74+/-0.48)x10^-3^ to (0.88+/-0.56)x10^-3^ objects per cubic parsec in the T1-T4.5 range. We notice that there seems to be an excess of objects in the L-T transition with respect to the late-T dwarfs, a discrepancy that could be explained assuming a higher binary fraction than expected for the L-T transition, or that objects in the high-mass end and low-mass end of this regime form in different environments, i.e. following different initial mass functions.
- ID:
- ivo://CDS.VizieR/J/ApJ/676/1281
- Title:
- L and T dwarfs in 2MASS/SDSS
- Short Name:
- J/ApJ/676/1281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report new L and T dwarfs found in a cross-match of the SDSS Data Release 1 and 2MASS. Our simultaneous search of the two databases effectively allows us to relax the criteria for object detection in either survey and to explore the combined databases to a greater completeness level. We find two new T dwarfs in addition to the 13 already known in the SDSS DR1 footprint. We also identify 22 new candidate and bona fide L dwarfs, including a new young L2 dwarf and a peculiar potentially metal-poor L2 dwarf with unusually blue near-IR colors. These discoveries underscore the utility of simultaneous database cross-correlation in searching for rare objects.
7799. L and T dwarf stars
- ID:
- ivo://CDS.VizieR/J/other/ARA+A/43.195
- Title:
- L and T dwarf stars
- Short Name:
- J/other/ARA+A/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The establishment of new spectral classes cooler than type M has had a brief, yet already rich, history. Prototypes of the new "L dwarf" and "T dwarf" classes were first found in the late 1980s to mid-1990s, with a flood of new discoveries occurring in the late 1990s with the advent of deep, large-area, digital sky surveys. Over four hundred and fifty L and T dwarfs are now catalogued. This review concentrates on the spectroscopic properties of these objects, beginning with the establishment of classification schemes rooted in the MK Process. The resulting grid of spectral types is then used as a tool to ferret out the underlying physics. The temperature ranges covered by these spectral types, the complex chemical processes responsible for the shape of their emergent spectra, their nature as either true stars or brown dwarfs, and their number density in the Galaxy are discussed. Two promising avenues for future research are also explored: the extension of the classification system to three dimensions to account for gravity- and metallicity-dependent features, and the capability of newer large-area surveys to uncover brown dwarfs cooler than those now recognized.
- ID:
- ivo://CDS.VizieR/J/ApJ/882/40
- Title:
- Lanthanide fraction distribution of metal-poor stars
- Short Name:
- J/ApJ/882/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multimessenger observations of the neutron star merger GW170817 and its kilonova proved that neutron star mergers can synthesize large quantities of r-process elements. If neutron star mergers in fact dominate all r-process element production, then the distribution of kilonova ejecta compositions should match the distribution of r-process abundance patterns observed in stars. The lanthanide fraction (X_La_) is a measurable quantity in both kilonovae and metal-poor stars, but it has not previously been explicitly calculated for stars. Here we compute the lanthanide fraction distribution of metal-poor stars ([Fe/H]{<}-2.5) to enable comparison to current and future kilonovae. The full distribution peaks at log X_La_~-1.8, but r-process-enhanced stars ([Eu/Fe]>0.7) have distinctly higher lanthanide fractions: logX_La_>~-1.5. We review observations of GW170817 and find general consensus that the total logX_La_=-2.2+/-0.5, somewhat lower than the typical metal-poor star and inconsistent with the most highly r-enhanced stars. For neutron star mergers to remain viable as the dominant r-process site, future kilonova observations should be preferentially lanthanide-rich (including a population of ~10% with logX_La_>-1.5). These high-X_La_ kilonovae may be fainter and more rapidly evolving than GW170817, posing a challenge for discovery and follow-up observations. Both optical and (mid-)infrared observations will be required to robustly constrain kilonova lanthanide fractions. If such high-X_La_ kilonovae are not found in the next few years, that likely implies that the stars with the highest r-process enhancements have a different origin for their r-process elements.