Different Classes Of Stars Research Articles

Li Distribution, Kinematics, and Detailed Abundance Analysis among Very Metal-poor Stars in the Galactic Halo from the HESP-GOMPA Survey

We present a study on the detailed elemental abundances of newly identified, bright, very metal-poor stars with the detection of lithium, initially observed as part of the SDSS/MARVELS pre-survey. These stars were selected for high-resolution spectroscopic follow-up as part of the HESP-GOMPA survey. In this work, we discuss the Li abundances detected for several stars in the survey, which include main-sequence stars, subgiants, and red giants. Different classes of stars are found to exhibit very similar distributions of Li, which points toward a common origin. We derive a scaling relation for the depletion of Li as a function of temperature for giants and main-sequence stars; the majority of the samples from the literature were found to fall within 1σ (0.19 and 0.12 dex K−1 for giants and dwarfs, respectively) of this relationship. We also report the existence of a slope of the Li abundance as a function of distance from the Galactic plane, indicating mixed stellar populations. Most Li-rich stars are found to be in or close to the Galactic plane. Along with Li, we have derived detailed abundances for C, odd-Z, α-, Fe-peak, and neutron-capture elements for each star. We have also used astrometric parameters from Gaia-EDR3 to complement our study, and derived kinematics to differentiate between the motions of the stars—those formed in situ and those accreted. The stellar population of the Spite plateau, including additional stars from the literature, is found to have significant contributions from stars formed in situ and through accretion. The orbits for the program stars have also been derived and studied for a period of 5 Gyr backwards in time.

Distances to Local Group Galaxies via Population II, Stellar Distance Indicators. II. The Fornax Dwarf Spheroidal* * Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5–26555. These observations are associated with program

We determine three independent Population II distance moduli to the Fornax dwarf spheroidal (dSph) galaxy, using wide-field, ground-based VI imaging acquired with the Magellan-Baade telescope at Las Campanas Observatory. After subtracting foreground stars using Gaia EDR3 proper motions, we measure an I-band tip of the red giant branch (TRGB) magnitude of mag, with a calibration based in the LMC giving a distance modulus of mag. We determine an RR Lyrae (RRL) distance from template mean magnitudes, with periods adopted from the literature. Adopting a Gaia DR2 calibration of first overtone RRL period–luminosity and period–Wesenheit relations, we find mag and mag. Finally, we determine a distance from Fornax’s horizontal branch (HB) and two galactic globular cluster calibrators, giving mag. These distances are each derived from homogeneous IMACS photometry, are anchored to independent geometric zero-points, and utilize different classes of stars. We therefore average over independent uncertainties and report the combined distance modulus 〈μ 0〉 =20.770 ± 0.042stat ± 0.024sys mag (corresponding to a distance of 143 ± 3 kpc).

Spatially resolved spectroscopy across stellar surfaces

Context. High-precision stellar analyses require hydrodynamic 3D modeling. Testing such models is feasible by retrieving spectral line shapes across stellar disks, using differential spectroscopy during exoplanet transits. Observations were presented in Papers I, II, and III, while Paper IV explored synthetic data at hyper-high spectral resolution for different classes of stars, identifying characteristic patterns for Fe I and Fe II lines. Aims. Anticipating future observations, the observability of patterns among photospheric lines of different strength, excitation potential and ionization level are examined from synthetic spectra, as observed at ordinary spectral resolutions and at different levels of noise. Time variability in 3D atmospheres induces changes in spectral-line parameters, some of which are correlated. An adequate calibration could identify proxies for the jitter in apparent radial velocity to enable adjustments to actual stellar radial motion. Methods. We used spectral-line patterns identified in synthetic spectra at hyper-high resolution in Paper IV from 3D models spanning Teff = 3964–6726 K (spectral types ~K8 V–F3 V) to simulate practically observable signals at different stellar disk positions at various lower spectral resolutions, down to λ/Δλ = 75 000. We also examined the center-to-limb temporal variability. Results. Recovery of spatially resolved line profiles with fitted widths and depths is shown for various noise levels, with gradual degradation at successively lower spectral resolutions. Signals during exoplanet transit are simulated. In addition to Rossiter-McLaughlin type signatures in apparent radial velocity, analogous effects are shown for line depths and widths. In a solar model, temporal variability in line profiles and apparent radial velocity shows correlations between jittering in apparent radial velocity and fluctuations in line depth. Conclusions. Spatially resolved spectroscopy using exoplanet transits is feasible for main-sequence stars. Overall line parameters of width, depth and wavelength position can be retrieved already with moderate efforts, but a very good signal-to-noise ratio is required to reveal the more subtle signatures between subgroups of spectral lines, where finer details of atmospheric structure are encoded. Fluctuations in line depth correlate with those in wavelength, and because both can be measured from the ground, searches for low-mass exoplanets should explore these to adjust apparent radial velocities to actual stellar motion.

Discrimination of artificial starry sky by pigeons.

Night migratory birds use the star compass for their navigation. Here, I examined discrimination of a starry sky by a nonmigratory bird, the pigeon. Four pigeons were trained in an operant chamber to discriminate between an artificial starry sky created using software (Stella Theater Pro) and a black sky without stars. After they learned the task, they received three generalization tests. Test 1 presented a starry sky with different classes of stars (i.e., the number of stars was changed). Test 2 presented a starry sky at different times (i.e., a horizontal shift of the sky). Test 3 presented a starry sky at different latitudes (i.e., a vertical shift of the sky). The pigeons displayed a clear generalization gradient with a peak shift to the sky with more stars in Test 1 and a peak close to the original sky in Test 3, but almost a flat gradient in Test 2. Therefore, pigeons demonstrated stimulus control using the pattern of the stars, and they were more sensitive to the vertical shift than to the horizontal shift.

Extinction law at a distance up to 25 kpc toward the Galactic poles

Photometry from the Tycho-2, 2MASS, and WISE catalogues for clump and branch giants at a distance up to 25 kpc toward the Galactic poles has allowed the variations of various characteristics of the infrared interstellar extinction law with distance to be analyzed. The results obtained by the extinction law extrapolation method are consistent for different classes of stars and different characteristics as well as with previous studies. The conventional extinction law with a low infrared extinction is characteristic of only a thin layer no farther than 100 pc from the Galactic plane and of two thin layers near $Z=-600$ and $+500$ pc. Far from the Galactic plane, in the Galactic halo, the infrared extinction law is different: the extinction in the $Ks$, $W1$, $W2$, $W3$, and $W4$ bands is, respectively, $0.17$, $0.16$, $0.16$, $0.07$, and $0.03$ of the extinction in the $V$ band. The accuracy of these coefficients is $0.03$. If the extinction law reflects primarily the grain size distribution, then the fraction of large dust grains far from the Galactic plane is greater than that in the circumsolar interstellar medium.

EXPLORING STELLAR EVOLUTION MODELS OF sdB STARS USING MESA

Stellar evolution calculations have had great success reproducing the observed atmospheric properties of different classes of stars. Recent detections of g-mode pulsations in evolved He burning stars allow a rare comparison of their internal structure with stellar models. Asteroseismology of subdwarf B (sdB) stars suggests convective cores of 0.22–0.28 M⊙, ≳45% of the total stellar mass. Previous studies found significantly smaller convective core masses (≲0.19 M⊙) at a comparable evolutionary stage. We evolved stellar models with Modules for Experiments in Stellar Astrophysics (MESA) to explore how well the interior structures inferred from asteroseismology can be reproduced by standard algorithms. Our qualitative evolutionary paths, position in the diagram, and model timescales are consistent with previous results. The sdB masses from our full evolutionary sequences fall within the range of the empirical sdB mass distribution, but are nearly always lower than the median. Using standard MLT with atomic diffusion we find convective core masses of ∼0.17–0.18 M⊙, averaged over the entire sdB lifetime. We can increase the convective core sizes to be as large as those inferred from asteroseismology, but only for extreme values of the overshoot parameter (overshoot gives numerically unstable and physically unrealistic behavior at the boundary). High resolution three-dimensional simulations of turbulent convection in stars suggest that the Schwarzschild criterion for convective mixing systematically underestimates the actual extent of mixing because a boundary layer forms. Accounting for this would decrease the errors in both sdB total and convective core masses.

Infrared composition of the Large Magellanic Cloud

AbstractThe evolution of galaxies and the history of star formation in the Universe are among the most important topics in today’s astrophysics. Especially, the role of small, irregular galaxies in the star-formation history of the Universe is not yet clear. Using the data from the AKARI IRC survey of the Large Magellanic Cloud at 3.2, 7, 11, 15, and 24 μm wavelengths, i.e., at the mid- and near-infrared, we have constructed a multiwavelength catalog containing data from a cross-correlation with a number of other databases at different wavelengths. We present the separation of different classes of stars in the LMC in color-color, and color-magnitude, diagrams, and analyze their contribution to the total LMC flux, related to point sources at different infrared wavelengths.

INFRARED COMPOSITION OF THE LARGE MAGELLANIC CLOUD

Understanding the birth and evolution of galaxies, and the history of star formation in them, is one of the most important problems in astronomy. Using the data from the AKARI IRC survey of the Large Magellanic Cloud at 3.2, 7, 11, 15, and , we have constructed a multi-wavelength catalog containing data from the cross-correlation with a number of other databases at different wavelengths. We present the first approach with a Support Vector Machine (SVM)-based method to separate different classes of stars in LMC in the color-color and color-magnitude diagrams.

Gravitational redshifts in main-sequence and giant stars

Gravitational redshifts in solar-type main-sequence stars are expected to be some 500 ms$^{-1}$ greater than those in giants. Such a signature is searched for between groups of open-cluster stars which share the same average space motion and thus have the same average Doppler shift. 144 main-sequence stars and cool giants were observed in the M67 open cluster using the ESO FEROS spectrograph, obtaining radial velocities by cross correlation with a spectral template. M67 dwarf and giant radial-velocity distributions are well represented by Gaussian functions, sharing the same apparent average radial velocity within $\simeq$ 100 ms$^{-1}$. In addition, dwarfs in M67 appear to be dynamically hotter ($\sigma$ = 0.90 kms$^{-1}$) than giants ($\sigma$ = 0.68 kms$^{-1}$). Explanations for the lack of an expected signal are sought: a likely cause is the differential wavelength shifts produced by different hydrodynamics in dwarf and giant atmospheres. Radial-velocity differences measured between unblended lines in low-noise averaged spectra vary with line-strength: stronger lines are more blushifted in dwarfs than in giants, apparently 'compensating' for the gravitational redshift. Synthetic high-resolution spectra are computed from 3-dimensional hydrodynamic model atmospheres for both giants and dwarfs, and synthetic wavelength shifts obtained. In agreement with observations, 3D models predict substantially smaller wavelength-shift differences than expected from gravitational redshift only. The procedures developed could be used to test 3D models for different classes of stars, but will ultimately require high-fidelity spectra for measurements of wavelength shifts in individual spectral lines.

Target star catalogue for Darwin Nearby Stellar sample for a search for terrestrial planets

In order to evaluate and develop mission concepts for a search for Terrestrial Exoplanets, we have prepared a list of potential target systems. In this paper we present and discuss the criteria for selecting potential target stars, suitable for the search for Earth-like planets, with a special emphasis on the aspects of the habitable zone for these stellar systems. Planets found within these zones would be potentially able to host complex life forms. We derive a final target star sample of potential target stars, the Darwin All Sky Star Catalogue (DASSC). The DASSC contains a sample of 2303 identified objects of which 284 are F-, 464 G-, 883 K- and 615 M-type stars and 57 stars without B-V index. Of these objects 949 objects are flagged in the DASSC as multiple systems, resulting in 1229 single main sequence stars of which 107 are F, 235 are G, 536 are K, and 351 are M type. We derive configuration dependent sub-catalogues from the DASSC for two technical designs, the initial baseline design and the advanced Emma design as well as a catalogue using an inner working angle cutoff. We discuss the selection criteria, derived parameters and completeness of sample for different classes of stars.

Target star catalogue for Darwin: Nearby Habitable Star Systems

In order to evaluate and develop mission concepts for a search for Terrestrial Exoplanets, the European Space Agency has prepared a list of potential target systems. In this paper we present the criteria for selecting potential target stars suitable for the search for Earth like planets. We also establish the habitable zone for the stellar systems. Planets found within these zones would be potentially able to host complex life forms. The Darwin target star catalogue was created from the Hipparcos catalogue by examining the information on distance, spectral classification, multiplicity and stellar variability. Additional information on the targets stars including spectral type, metallicity, X-ray luminosity, rotation and Stromgren photometry from several other catalogues are included to determine the target star sample. Design constraints of the mission are added to derive a final target star catalogue of 262 target stars excluding and 447 target stars including M stars for the Darwin mission. We also discuss the completeness of sample for different classes of stars.

Coronagraphic search for exo-planets with a hypertelescope

Following the idea developed in Boccaletti et al. (2000), a snapshot imaging interferometer is proposed as an alternative to the nulling interferometer for the NASA Origin project, “Terrestrial Planet Finder". This concept is based on hypertelescope, i.e. densified-pupil, imaging (Labeyrie [CITE]) and phase-mask coronagraphy (Rouan et al. [CITE]) to combine a very high angular resolution and a deep attenuation of starlight (10-8) as required to image extra-terrestrial planets. This article aims at presenting thorough estimations of the signal to noise ratio for different classes of stars (from F0V to M5V) and includes several sources of background noise (zodiacal and exozodiacal lights for instance). In addition, numerical simulations have been carried out and are compared to the analytical results. We find that the image of Earth-like planets can be formed with a large hypertelescope (~80 m) in the thermal infra-red for about 73% of the stars within 25pc.

Atmospheres and Abundances of Blue Horizontal Branch Stars and Related Objects

Spectroscopic analyses of blue horizontal branch stars, subluminous B- and O-stars and PG 1159 stars are reviewed. These classes of stars trace stellar evolution from the horizontal branch towards the white dwarf cooling sequence. The impact of Non-LTE model atmospheres for the analyses of sdO and PG 1159 stars is outlined. The resulting atmospheric parameters and abundances are used to obtain constraints on the evolutionary status of the different classes of stars. The sdB stars form a homogeneous group and can be identified with models of the extended horizontal branch. Abundance anomalies (deficiency of helium and some metals, enrichment of 3He) observed in Horizontal Branch stars and sdB stars do not give hints to the stars' evolutionary history but are caused by atmospheric diffusion. The class of subluminous O stars is much less homogenous and two subclasses can be defined: the “compact” sdO stars probably evolved from the extended horizontal branch and are hence successors of the sdBs, whereas some sdOs of relatively low gravity are in a post-AGB stage of evolution. The third class, the PG 1159 stars, are amongst the hottest stars known with effective temperatures exceeding 100,000 K and are immediate progenitors of the white dwarfs. The abundance pattern is dominated by carbon and helium with a significant admixture of oxygen, whereas hydrogen and nitrogen are trace elements only. As in the case of the (helium rich) sdO stars these abundances indicate that nuclear processed material is exposed at the stellar surface. The origin of the PG 1159 stars as well as of the “low gravity” sdO stars can be explained by the born-again post-AGB star scenario of Iben et al. (1983).

Contribution of Soviet-Bolivian Astronomical Observatory in the Construction of the Inertial Coordinate System

The work on photographic astrometry in Bolivia begun in 1983, when an expeditional astrograph was put there (D=23 cm, F=230 cm, working field of 4°x4°). The main purpose of the observations with this telescope is extending the inertial coordinate system to different classes of stars. For this purpose we have carried out and are currently carrying out the following observational astrometric programs:1. The preliminary catalog of precise positions of 200 000 southern stars to mag 11 with declination in the range from 0° to −90° was created. Each star was observed four times with displacement of the photoplate by 2° in δ and by 8 secδ in α. The exposure time is from 4 to 12 minutes. The accuracy of the preliminary catalog is ±0.247 arcsec and the final one is ±0.15 arcsec.2. We are not far from finishing the work on a catalog of 1900 bright stars (−90° < δ; 0°, m ≥ 6.05). Each star was observed not less than 2 times for different positions of a special filter which diminished the light of bright stars.3. The work on astrometry of equatorial stars to mag 12 in the range of declination from −20° to +20° was begun. From the beginning of the observations on 1 May 1987, 1150 astroplates were obtained. On the whole it is necessary to obtain 3840 photoplates. All three programs use the reference catalog SRS, compiled by Pulkovo and Washington astronomers, in the FK5 system.

Our Astronomical Column

INFRA-RED STELLAR SPECTRA.—Some interesting experiments on the photography of stellar spectra in the extreme red have been made by Dr. P. W. Merrill, of the Bureau of Standards, Washington (Scientific Papers, No. 318). The actual tests were made at the Harvard College Observatory, where use was made of the 24-in. reflector, combined with objective prisms of different dispersions. The plates were sensitised for the red by staining with dicyanin, and pinaverdol was added when it was desired to photograph the yellow and green in addition. A large number of spectra of typical stars was obtained, with exposures ranging from 5 to 112 minutes, reaching in some cases as far as λ870, and showing the, atmospheric absorption bands B, a, and A. Several examples are reproduced, and it is clear that results of considerable value to astronomers and physicists may be obtained in the future by this method. Among other results of interest Dr. Merrill has found a new absorption band in the spectra of the M stars at wave-length 760, which he has proved by laboratory experiments to belong to the titanium-oxide series; in Mira there is possibly still another band between 810 and 820. In stars of class N new bands have been found at 692, 708, and 723, and these differ from the characteristic bands of carbon in degenerating towards the less refrangible part of the spectrum; it is suggested that they may possibly be due to cyanogen. The great contrast in energy distribution in the different classes of stars is very strongly emphasised by the extended range of observation, For classes B and A the blue portion is much the stronger; at class K the blue and red are about equal; while for classes M and N the red is the stronger.

Our Astronomical Column

THE NEBULIE AND STELLAR EVOLUTIONA—A full report of Prof. W. W. Campbells address as retiring president of the American Association for the Advancernent,of Science is given in Science (vol. xlv., No. i 169). The subject chosen was The Nebul, and, besides giving an interesting account of the development of our knowledge of these objects, with an abundance of fine ifiustrations,. Prof. Campbell clearly stated his views as to the place of the nebuke in the cosmical scheme. As to the spiral nebuke, Prof. Campbell considers the hypothesis that they are independent stellar systems, or external universes, to be in best harmony with the known facts. As regards the gaseous nebuke, while a strong case can be made out for the evolution of planetary nebuke into stars, it cannot safely be concluded that all stars have been developed from nebuke of this class; their comparative scarcity and their relatively high velocities are decidedly against such a conclusion. A much stronger case can be made out for the hypothesis that the stars in general have evolved from irregular nehuke, which have spectra identical with those of the planetaries. These nbulai are closely related spectroscopically to the bright-line stars, and these again to the early class B stars, and from thence the sequence can be traced through the Sirian and solar types to the red stars. This is regarded by Prof. Campbell as the most probable course of stellar evolution. Facts as to the distribution of ndbulre and of the different classes of stars seem to him to be opposed to the view that some of the red stars may be at an early stage of evolution.

The Classification of Helium Stars

WHILE it is now generally admitted that the spectroscopic differences between the different classes of stars are mainly due to differences of temperature, there are two widely divergent views as to the order of celestial evolution which may be inferred. In one of them, the evolution is supposed to proceed by a continuous ecline of temperature from the white to the red stars; in the other, which has been consistently advocated by Sir Norman Lockyer during nearly thirty years, it is maintained that the progression is from stars at a low stage of temperature to the hottest stars, and from these to stars at. a low temperature, so that a given star will have the same temperature twice in the course of its evolution. The classifications of Rutherfurd, Secchi, and Vogel, and the expansion of these into the Harvard system, may be interpreted in terms of the first hypothesis, though actually they may be regarded as merely empirical and independent of any such consideration. The classification of Lockyer, on the other hand, is essentially based upon the supposition that there must be stars which are getting hotter as well as stars which are cooling, in accordance with the theory of condensing masses of gas or swarms of meteorites.