- ID:
- ivo://CDS.VizieR/J/ApJ/816/70
- Title:
- High resolution spectra of 3 NGC104 member stars
- Short Name:
- J/ApJ/816/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters are known to host peculiar objects named blue straggler stars (BSSs), significantly heavier than the normal stellar population. While these stars can be easily identified during their core hydrogen-burning phase, they are photometrically indistinguishable from their low-mass sisters in advanced stages of the subsequent evolution. A clear-cut identification of these objects would require the direct measurement of the stellar mass. We used the detailed comparison between chemical abundances derived from neutral and from ionized spectral lines as a powerful stellar "weighing device" to measure stellar mass and to identify an evolved BSS in 47Tucanae. In particular, high-resolution spectra of three bright stars, located slightly above the level of the "canonical" horizontal branch (HB) sequence in the color-magnitude diagram of 47 Tucanae, have been obtained with the UVES spectrograph. The measurements of iron and titanium abundances performed separately from neutral and ionized lines reveal that two targets have stellar parameters fully consistent with those expected for low-mass post-HB objects, while for the other target the elemental ionization balance is obtained only by assuming a mass of ~1.4M_{sun}_, which is significantly larger than the main sequence turn-off mass of the cluster (~0.85M_{sun}_). The comparison with theoretical stellar tracks suggests that this is a BSS descendant possibly experiencing its core helium-burning phase. The large applicability of the proposed method to most of the globular clusters in our Galaxy opens the possibility to initiate systematic searches for evolved BSSs, thus giving access to still unexplored phases of their evolution.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/846/23
- Title:
- High-resolution spectra of 9 RGB stars in NGC6681
- Short Name:
- J/ApJ/846/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain high-resolution spectra of nine red giant branch stars in NGC 6681 and perform the first detailed abundance analysis of stars in this cluster. We confirm cluster membership for these stars based on consistent radial velocities of 214.5+/-3.7km/s and find a mean [Fe/H]=-1.63+/-0.07dex and [{alpha}/Fe]=0.42+/-0.11dex. Additionally, we confirm the existence of a Na-O anti-correlation in NGC 6681 and identify two populations of stars with unique abundance trends. With the use of HST photometry from Sarajedini+ (2007AJ....133.1658S) and Piotto+ (2015AJ....149...91P) we are able to identify these two populations as discrete sequences in the cluster CMD. Although we cannot confirm the nature of the polluter stars responsible for the abundance differences in these populations, these results do help put constraints on possible polluter candidates.
- ID:
- ivo://CDS.VizieR/J/ApJS/248/19
- Title:
- High-resolution spectroscopy of TESS stars
- Short Name:
- J/ApJS/248/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate atmospheric parameters and chemical composition of stars play a vital role in characterizing physical parameters of exoplanetary systems and understanding of their formation. A full asteroseismic characterization of a star is also possible if its main atmospheric parameters are known. The NASA Transiting Exoplanet Survey Satellite (TESS) space telescope will play a very important role in searching of exoplanets around bright stars and stellar asteroseismic variability research. We have observed all 302 bright (V<8mag) and cooler than F5 spectral class stars in the northern TESS continuous viewing zone with a 1.65m telescope at the Moletai Astronomical Observatory of Vilnius University and the high-resolution Vilnius University Echelle Spectrograph. We uniformly determined the main atmospheric parameters, ages, orbital parameters, velocity components, and precise abundances of 24 chemical species (C(C2), N(CN), [OI], NaI, MgI, AlI, SiI, SiII, CaI, CaII, ScI, ScII, TiI, TiII, VI, CrI, CrII, MnI, FeI, FeII, CoI, NiI, CuI, and ZnI) for 277 slowly rotating single stars in the field. About 83% of the sample stars exhibit the Mg/Si ratios greater than 1.0 and may potentially harbor rocky planets in their systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/848/18
- Title:
- High-res. spectroscopic obs. of 2 Herbig stars
- Short Name:
- J/ApJ/848/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent observational work has indicated that mechanisms for accretion and outflow in Herbig Ae/Be star-disk systems may differ from magnetospheric accretion (MA) as it is thought to occur in T Tauri star-disk systems. In this work, we assess the temporal evolution of spectral lines probing accretion and mass loss in Herbig Ae/Be systems and test for consistency with the MA paradigm. For two Herbig Ae/Be stars, HD 98922 (B9e) and V1295 Aql (A2e), we have gathered multi-epoch (~years) and high-cadence (~minutes) high-resolution optical spectra to probe a wide range of kinematic processes. Employing a line equivalent width evolution correlation metric introduced here, we identify species co-evolving (indicative of common line origin) via novel visualization. We interferometrically constrain often problematically degenerate parameters, inclination and inner-disk radius, allowing us to focus on the structure of the wind, magnetosphere, and inner gaseous disk in radiative transfer models. Over all timescales sampled, the strongest variability occurs within the blueshifted absorption components of the Balmer series lines; the strength of variability increases with the cadence of the observations. Finally, high-resolution spectra allow us to probe substructure within the Balmer series' blueshifted absorption components: we observe static, low-velocity features and time-evolving features at higher velocities. Overall, we find the observed line morphologies and variability are inconsistent with a scaled-up T Tauri MA scenario. We suggest that as magnetic field structure and strength change dramatically with increasing stellar mass from T Tauri to Herbig Ae/Be stars, so too may accretion and outflow processes.
- ID:
- ivo://CDS.VizieR/J/ApJ/877/104
- Title:
- High-res. spectroscopy of LAMOST Li-rich giants
- Short Name:
- J/ApJ/877/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of Li-rich giants has introduced a new challenge for standard stellar evolution models. To resolve this issue, the number of this type of object has been rapidly increased through the development of worldwide surveys. Taking advantage of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, 44 new Li-rich giants are reported, which are confirmed with high-resolution observations. Based on the high-resolution and high signal-to-noise spectra, we derived the atmospheric parameters and elemental abundances with the spectral synthesis method. We performed a detailed analysis of their evolutionary stages, infrared excess, projected rotational velocity (vsini), and stellar population. We find that (1) the Li-rich giants concentrate at the evolutionary status of the red giant branch bump, red clump, and asymptotic giant branch; (2) three of them are fast rotators and none exhibit infrared excess. Our results imply that the origins of Li enrichment are most likely to be associated with the extra mixing in the stellar interior, and the external sources might only make a minor contribution. Moreover, various Li-rich episodes take place at different evolutionary stages.
- ID:
- ivo://CDS.VizieR/J/ApJS/252/3
- Title:
- High-velocity stars in the Gal. halo from LAMOST & Gaia
- Short Name:
- J/ApJS/252/3
- Date:
- 03 Mar 2022 11:59:54
- Publisher:
- CDS
- Description:
- In this paper, we report 591 high-velocity star candidates (HiVelSCs) selected from over 10 million spectra of Data Release 7 (DR7) of the Large Sky Area Multi-object Fiber Spectroscopic Telescope and the second Gaia data release, with three-dimensional velocities in the Galactic rest frame larger than 445km/s. We show that at least 43 HiVelSCs are unbound to the Galaxy with escape probabilities larger than 50%, and this number decreases to eight if the possible parallax zero-point error is corrected. Most of these HiVelSCs are metal-poor and slightly {alpha}-enhanced inner halo stars. Only 14% of them have [Fe/H]>-1, which may be the metal-rich "in situ" stars in the halo formed in the initial collapse of the Milky Way or metal-rich stars formed in the disk or bulge but kinematically heated. The low ratio of 14% implies that the bulk of the stellar halo was formed from the accretion and tidal disruption of satellite galaxies. In addition, HiVelSCs on retrograde orbits have slightly lower metallicities on average compared with those on prograde orbits; meanwhile, metal-poor HiVelSCs with [Fe/H]{<}-1 have an even faster mean retrograde velocity compared with metal-rich HiVelSCs. To investigate the origins of HiVelSCs, we perform orbit integrations and divide them into four types, i.e., hypervelocity stars, hyper-runaway stars, runaway stars and fast halo stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/594/1
- Title:
- High-z supernovae VRI mag and distances
- Short Name:
- J/ApJ/594/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The High-z Supernova Search Team has discovered and observed eight new supernovae in the redshift interval z=0.3-1.2. These independent observations, analyzed by similar but distinct methods, confirm the results of Riess (1998AJ....116.1009R) and Perlmutter (1999ApJ...517..565P) and coworkers that supernova luminosity distances imply an accelerating universe.
- ID:
- ivo://CDS.VizieR/J/A+A/476/89
- Title:
- HII galaxies narrow-band Hbeta images
- Short Name:
- J/A+A/476/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aims is to create a catalog of images of HII galaxies and their individual star-formation regions in order to study the distribution of the gas emission and their underlying stellar continuum. We have used H{beta} narrow-band images of 43 selected HII galaxies obtained at ESO NTT 3.58m telescope using the SUSI2 camera. Surface photometric H{beta} fluxes and equivalent widths for all objects and star-formation regions are presented in this catalog.
- ID:
- ivo://CDS.VizieR/J/MNRAS/297/255
- Title:
- HII region catalogue of M100
- Short Name:
- J/MNRAS/297/255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From a new mosaic image in the H-{alpha} line of the complete disc of the spiral galaxy M100, a catalogue is composed listing 1948 individual HII regions. For each HII region, the catalogue gives its position relative to the centre of the galaxy, its deprojected distance to the centre, its radius, and its calibrated luminosity. An indication is included as to whether the HII region is located in the arms, between them, or in the circumnuclear star-forming region. The H-{alpha} image of M100 was obtained during two observing runs with the 4.2m WHT on La Palma, using the TAURUS camera in imaging mode. Since the field of view in this setup is limited by the filter size to around 5' diameter, four fields of the galaxy were imaged, two (eastern half of M100) during the night of 27 May 1991, and two (western half) during the night of 14 March 1992. Narrow band redshifted H-{alpha} filters with width of 15{AA} were used for the observations, centred at 6601{AA} for the H-{alpha} line observations (redshifted using the galaxy's systemic velocity of 1571km/s) and at 6577{AA} and 6565{AA} for the continuum. Exposure times were 1200 seconds for both the on-line and the continuum image on the first night, and 2x900 seconds on the second night. An EEV CCD chip was used during both observing runs, with a projected pixel size of 0.279arcsec, and a size of 1180x1280 pixels.
- ID:
- ivo://CDS.VizieR/J/A+AS/135/145
- Title:
- HII region catalogue of NGC 7479
- Short Name:
- J/A+AS/135/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HII region catalogue of the barred galaxy NGC 7479. The catalogue contains the position, mean radius and the calibrated H-alpha luminosity of each HII region. The HII region catalogue has been composed using a new semi-automated technique applied to a high quality continuum-subtracted H-alpha image of the galaxy obtained from observations through the TAURUS camera in imaging mode with the 4.2m WHT on La Palma. An EEV CCD 7 detector was used with a projected pixel size of 0.279". More details about the reduction and the catalogue production procedures are given in the paper.
