- ID:
- ivo://CDS.VizieR/J/ApJ/836/167
- Title:
- K2 planetary syst. around low-mass stars. I.
- Short Name:
- J/ApJ/836/167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1-7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3-M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13R_{sun}_ (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.
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Search Results
- 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/MNRAS/468/1123
- Title:
- LAE among star-forming galaxies at z=2.5
- Short Name:
- J/MNRAS/468/1123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a deep narrow-band imaging survey with the Subaru Prime Focus Camera on the Subaru Telescope and constructed a sample of Ly{alpha} emitters (LAEs) at z=2.53 in the UDS-CANDELS field, where a sample of H{alpha} emitters (HAEs) at the same redshift is already obtained from our previous narrow-band observation at near-infrared. The deep narrow-band and multibroad-band data allow us to find LAEs of stellar masses and star formation rates (SFRs) down to >=10^8^M_{sun}_ and >=0.2 M_{sun}_/yr, respectively. We show that the LAEs are located along the same mass-SFR sequence traced by normal star-forming galaxies such as HAEs, but towards a significantly lower mass regime. Likewise, LAEs seem to share the same mass-size relation with typical star-forming galaxies, except for the massive LAEs that tend to show significantly compact sizes. We identify a vigorous mass growth in the central part of LAEs: the stellar mass density in the central region of LAEs increases as their total galaxy mass grows. On the other hand, we see no Ly{alpha} line in emission for most of the HAEs. Rather, we find that the Ly{alpha} feature is either absent or in absorption (Ly{alpha} absorbers, LAAs), and its absorption strength may increase with reddening of the UV continuum slope. We demonstrate that a deep Ly{alpha} narrow-band imaging like this study is able to search for not only LAEs but also LAAs in a certain redshift slice. This work suggests that LAEs trace normal star-forming galaxies in the low-mas
- ID:
- ivo://CDS.VizieR/J/ApJ/845/172
- Title:
- LAE candidates around bright Ly{alpha} blobs
- Short Name:
- J/ApJ/845/172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Bright Ly{alpha} blobs (LABs)-extended nebulae with sizes of ~100kpc and Ly{alpha} luminosities of ~10^44^erg/s -- often reside in overdensities of compact Ly{alpha} emitters (LAEs) that may be galaxy protoclusters. The number density, variance, and internal kinematics of LABs suggest that they themselves trace group-like halos. Here, we test this hierarchical picture, presenting deep, wide-field Ly{alpha} narrowband imaging of a 1{deg}x0.5{deg} region around a LAB pair at z=2.3 discovered previously by a blind survey. We find 183 Ly{alpha} emitters, including the original LAB pair and three new LABs with Ly{alpha} luminosities of (0.9-1.3)x10^43^erg/s and isophotal areas of 16-24arcsec^2^. Using the LAEs as tracers and a new kernel density estimation method, we discover a large-scale overdensity (Bootes J1430+3522) with a surface density contrast of {delta}_{Sigma}_=2.7, a volume density contrast of {delta}~10.4, and a projected diameter of ~20 comoving Mpc. Comparing with cosmological simulations, we conclude that this LAE overdensity will evolve into a present-day Coma-like cluster with log(M/M_{sun}_)~15.1+/-0.2. In this and three other wide-field LAE surveys re-analyzed here, the extents and peak amplitudes of the largest LAE overdensities are similar, not increasing with survey size, and implying that they were indeed the largest structures then and today evolve into rich clusters. Intriguingly, LABs favor the outskirts of the densest LAE concentrations, i.e., intermediate LAE overdensities of {delta}_{Sigma}_=1-2. We speculate that these LABs mark infalling protogroups being accreted by the more massive protocluster.
- ID:
- ivo://CDS.VizieR/J/ApJ/744/110
- Title:
- LAE galaxies between 2.1=<z<=3.1
- Short Name:
- J/ApJ/744/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the results of a new, wide-field survey for z=3.1 Ly{alpha} emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S). By using a nearly top-hat 5010{AA} filter and complementary broadband photometry from the MUSYC survey, we identify a complete sample of 141 objects with monochromatic fluxes brighter than 2.4x10^-17^erg/cm^2^/s and observers-frame equivalent widths (EWs) greater than ~80{AA} (i.e., 20{AA} in the rest frame of Ly{alpha}). The bright end of this data set is dominated by X-ray sources and foreground objects with Galaxy Evolution Explorer detections, but when these interlopers are removed, we are still left with a sample of 130 LAE candidates, 39 of which have spectroscopic confirmations. This sample overlaps the set of objects found in an earlier ECDF-S survey, but due to our filter's redder bandpass, it also includes 68 previously uncataloged sources. We confirm earlier measurements of the z=3.1 LAE emission-line luminosity function and show that an apparent anticorrelation between EW and continuum brightness is likely due to the effect of correlated errors in our heteroskedastic data set. Finally, we compare the properties of z=3.1 LAEs to LAEs found at z=2.1. We show that in the ~1Gyr after z~3, the LAE luminosity function evolved significantly, with L* fading by ~0.4mag, the number density of sources with L>1.5x10^42^erg/s declining by ~50%, and the EW scale length contracting from 70^+7^_-5_{AA} to 50^+9^_-6_{AA}. When combined with literature results, our observations demonstrate that over the redshift range z~0 to z~4, LAEs contain less than ~10% of the star formation rate density of the universe.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/762
- Title:
- LAEs at z~4.5 in the LALA Cetus field
- Short Name:
- J/ApJ/706/762
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a large sample of Ly{alpha}-emitting galaxies (LAEs) spectroscopically confirmed at redshift z~4.5, based on Inamori-Magellan Areal Camera and Spectrograph spectroscopic observations of candidate z~4.5 Ly{alpha}-emitting galaxies in the large area Lyman alpha (LALA) narrowband imaging survey Cetus field. We identify 110 of them as z~4.5 Ly{alpha} emitters based on single-line detections with no continuum emission blueward of the line. Six foreground galaxies are identified, either based on multiple lines or blueward continuum emission. The Ly{alpha} confirmation rate varies from <50% to 76% for candidates selected in different narrowband filters at slightly different redshifts. The sample includes many objects with equivalent widths (EWs)>~200{AA}. These large EW candidates are spectroscopically confirmed at the same rate as candidates with more modest EWs.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/136
- Title:
- LAEs between 0.19<z<1.25 with GALEX grism
- Short Name:
- J/ApJ/738/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical spectroscopy of two samples of Galaxy Evolution Explorer grism selected Ly{alpha} emitters (LAEs): one at z=0.195-0.44 and the other at z=0.65-1.25. We have also observed a comparison sample of galaxies in the same redshift intervals with the same UV magnitude distributions but with no detected Ly{alpha}. We use the optical spectroscopy to eliminate active galactic nuclei and to obtain the optical emission-line properties of the samples. We compare the luminosities of the LAEs in the two redshift intervals and show that there is dramatic evolution in the maximum Ly{alpha} luminosity over z=0-1. Focusing on the z=0.195-0.44 samples alone, we show that there are tightly defined relations between all of the galaxy parameters and the rest-frame equivalent width (EW) of H{alpha}. The higher EW(H{alpha}) sources all have lower metallicities, bluer colors, smaller sizes, and less extinction, consistent with their being in the early stages of the galaxy formation process.
- ID:
- ivo://CDS.VizieR/J/AJ/121/2124
- Title:
- {lambda} Ori pre-main-sequence stars photometry
- Short Name:
- J/AJ/121/2124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The {lambda} Ori star-forming region presents a snapshot of a moderate-mass giant molecular cloud 1-2Myr after cloud disruption by OB stars, with the OB stars, the low-mass stellar population, remnant molecular clouds, and the dispersed gas all still present. We have used optical photometry and multiobject spectroscopy for lithium absorption to identify 266 pre-main-sequence stars in 8deg^2^ of the region. We also present new Stroemgren photometry for the massive stars, from which we derive a distance of 450pc and a turnoff age of 6-7Myr. Using these parameters and pre-main-sequence evolutionary models, we map the star formation history of the low-mass stars. We find that low-mass star formation started throughout the region at about the same time as the birth of the massive stars, and thereafter the birth rate accelerated. Within the last 1-2Myr star formation ceased in the center of the star-forming region, near the concentration of OB stars, while it continues in dark clouds 20pc away. We suggest that a supernova 1-2Myr ago destroyed the molecular cloud core from which the OB stars formed, but it did not terminate star formation in more distant reaches of the giant molecular cloud. We find no secure evidence for triggered or sequential star formation in the outer molecular clouds. The global star formation of the {lambda} Ori region has generated the field initial mass function, but local star formation in subregions shows large deviations from the expected ratio of high- to low-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/594/A39
- Title:
- LAMOST-Kepler parameters and activity indicators
- Short Name:
- J/A+A/594/A39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A comprehensive and homogeneous determination of stellar parameters for the stars observed by the Kepler space telescope is necessary for statistical studies of their properties. As a result of the large number of stars monitored by Kepler, the largest and more complete databases of stellar parameters published to date are multiband photometric surveys. The LAMOST-Kepler survey, whose spectra are analyzed in the present paper, was the first large spectroscopic project, which started in 2011 and aimed at filling that gap. In this work we present the results of our analysis, which is focused on selecting spectra with emission lines and chromospherically active stars by means of the spectral subtraction of inactive templates. The spectroscopic determination of the atmospheric parameters for a large number of stars is a by-product of our analysis. We have used a purposely developed version of the code ROTFIT for the determination of the stellar parameters by exploiting a wide and homogeneous collection of real star spectra, namely the Indo US library. We provide a catalog with the atmospheric parameters (Teff, logg, and [Fe/H]), radial velocity (RV), and an estimate of the projected rotation velocity (vsini). For cool stars (Teff<6000K), we also calculated the H-alpha and CaII-IRT fluxes, which are important proxies of chromospheric activity. We have derived the RV and atmospheric parameters for 61753 spectra of 51385 stars. The average uncertainties, which we estimate from the stars observed more than once, are about 12km/s, 1.3%, 0.05dex, and 0.06dex for RV, Teff, logg, and [Fe/H], respectively, although they are larger for the spectra with a very low signal-to-noise ratio. Literature data for a few hundred stars (mainly from high-resolution spectroscopy) were used to peform quality control of our results. The final accuracy of the RV is about 14km/s. The accuracy of the Teff, logg, and [Fe/H] measurements is about 3.5%, 0.3dex, and 0.2dex, respectively. However, while the Teff values are in very good agreement with the literature, we noted some issues with the determination of [Fe/H] of metal poor stars and the tendency, for logg, to cluster around the values typical for main-sequence and red giant stars. We propose correction relations based on these comparisons and we show that this does not have a significant effect on the determination of the chromospheric fluxes. The RV distribution is asymmetric and shows an excess of stars with negative RVs that are larger at low metallicities. Despite the rather low LAMOST resolution, we were able to identify interesting and peculiar objects, such as stars with variable RV, ultrafast rotators, and emission-line objects. Based on the H-alpha and CaII-IRT fluxes, we found 442 chromospherically active stars, one of which is a likely accreting object. The availability of precise rotation periods from the Kepler photometry allowed us to study the dependency of these chromospheric fluxes on the rotation rate for a very large sample of field stars.
- ID:
- ivo://CDS.VizieR/J/AJ/155/189
- Title:
- LAMOST Quasar Survey: quasar properties from DR2&3
- Short Name:
- J/AJ/155/189
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second installment for the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Quasar Survey, which includes quasars observed from 2013 September to 2015 June. There are 9024 confirmed quasars in DR2 and 10911 in DR3. After cross-match with the Sloan Digital Sky Survey (SDSS) quasar catalogs and NED, 12126 quasars are discovered independently. Among them, 2225 quasars were released by SDSS DR12 QSO catalog in 2014 after we finalized the survey candidates. 1801 sources were identified by SDSS DR14 as QSOs. The remaining 8100 quasars are considered as newly founded, and among them, 6887 quasars can be given reliable emission line measurements and the estimated black hole masses. Quasars found in LAMOST are mostly located at low-to-moderate redshifts, with a mean value of 1.5. The highest redshift observed in DR2 and DR3 is 5. We applied emission line measurements to H{alpha}, H{beta}, Mg II, and C IV. We deduced the monochromatic continuum luminosities using photometry data, and estimated the virial black hole masses for the newly discovered quasars. Results are compiled into a quasar catalog, which will be available online.
