scholarly journals Surface gravity and effective temperature of the K5 subdwarf G 224-58 A and Arcturus from the fits to Ti and MgH lines

2016 ◽  
Vol 6 (1) ◽  
pp. 16-19
Author(s):  
I. Kushniruk ◽  
Ya. Pavlenko ◽  
M. Gálvez-Ortiz ◽  
Z. Zhang
Keyword(s):  
The Sun ◽  
Late Type ◽  
Selected Lines ◽  
Synthetic Spectra ◽  
Self Consistent ◽  
Minimization Procedure ◽  
Effective Temperatures ◽  
Red Giant ◽  
Consistent Approach

We discuss here the results obtained in the determination of effective temperatures and metallicities of late-type stars. We provide the abundances of MgH, TiI and TiII, with a list of selected lines, for the red giant of Arcturus and the metal-poor K subdwarf G 224-58 A. The Sun was used as a template star. After computing synthetic spectra for model atmospheres with different Teff and logg values, we used minimization procedures to determine the best fits to the observed features. The determination of Ti abundances was carried out in the framework of a self-consistent approach developed by Pavlenko et al. (2012). In the case of MgH we used similar minimization procedure. We present here the combination of two different approaches based on the fits performed to Ti and MgH, respectively. The resulting effective temperatures are Teff=4300 K for Arcturus and Teff=4600 K for G 224-58 A, where both solutions are degenerated with logg.

Galactic Infrared Astronomy

1971 ◽  
Vol 2 (1) ◽  
pp. 14-20 ◽  
Author(s):  
A. R. Hyland
Keyword(s):  
Interstellar Extinction ◽  
Infrared Astronomy ◽  
The Sun ◽  
Late Type ◽  
Infrared Observations ◽  
Effective Temperatures

Until the last six years few infrared observations of astronomical objects (other than the Sun and planets) had been attempted. Those few were primarily concerned with obtaining bolometric corrections and effective temperatures, the variation of bolometric magnitudes of late-type variables, and the derivation of the laws of interstellar extinction.

scholarly journals Applications of Narrow-Band Photometry in the Study of Peculiar Red Giants

2000 ◽  
Vol 177 ◽  
pp. 127-140
Author(s):  
Robert F. Wing
Keyword(s):  
Near Infrared ◽  
Narrow Band ◽  
Red Giants ◽  
Late Type ◽  
Energy Distributions ◽  
Synthetic Spectra ◽  
Continuum Energy ◽  
Qualitative Classification ◽  
Effective Temperatures ◽  
Classification Recognition

Narrow-band photometry, carried out with filters or spectrum scanners, is useful for measuring molecular bandstrengths and continuum energy distributions in late-type stars. This review emphasizes observations by the writer on three different multicolor photometric systems in the near infrared (0.75 − 4.0 μm); a summary of available data is given. While applications to date have been primarily qualitative (classification, recognition of peculiarities, relative temperatures), future applications are expected to be quantitative (determinations of effective temperatures, luminosities, and abundances) and based upon comparison with synthetic spectra.

scholarly journals Abundances in the atmosphere of the metal-rich planet-host star HD 77338

2014 ◽  
Vol 4 (1-2) ◽  
pp. 20-24 ◽  
Author(s):  
I. Kushniruk ◽  
Ya. Pavlenko ◽  
J. Jenkins ◽  
H.R.A. Jones
Keyword(s):  
Single Star ◽  
Self Consistent ◽  
Iron Abundance ◽  
Consistent Approach

Abundances of Fe, Si, Ni, Ti, Na, Mg, Cu, Zn, Mn, Cr and Ca in the atmosphere of the K-dwarf HD 77338 are determined and discussed. HD 77338 hosts a hot Uranus-like planet and is currently the most metal-rich single star to host any planet. Determination of abundances was carried out in the framework of a self-consistent approach developed by Pavlenko et al. (2012). Abundances were computed iteratively by the ABEL8 code, and the process converged after 4 iterations. We find that most elements follow the iron abundance, however some of the iron peak elements are found to be over-abundant in this star.

scholarly journals Spectroscopic distances to late-type stars

2012 ◽  
Vol 8 (S289) ◽  
pp. 83-86
Author(s):  
Maria Bergemann ◽  
Aldo Serenelli ◽  
Gregory Ruchti
Keyword(s):  
Stellar Evolution ◽  
Large Scale ◽  
Local Thermodynamic Equilibrium ◽  
Systematic Errors ◽  
Spectroscopic Techniques ◽  
The Sun ◽  
Late Type ◽  
Non Local ◽  
Ionization Balance

AbstractA common approach to determining distances to stars without astrometric information is to compare stellar evolution models with parameters obtained from spectroscopic techniques. This method is routinely applied in the context of large-scale stellar surveys out to distances of several kpc. However, systematic errors may arise because of inaccurate spectroscopic parameters. We explore the effects of non-local thermodynamic equilibrium (NLTE) on the determination of surface gravities and metallicities for a large sample of metal-poor stars within approximately 10 kpc of the Sun. Using the improved Teff scale, we then show that stellar parameters estimated based on the widely used method of 1D LTE excitation-ionization balance of Fe results in distances which are systematically in error. For metal-poor giants, [Fe/H] ~ −2 dex, the distances can be overestimated by up to 70%. We compare the results with those from the Radial Velocity Experiment Survey catalogue (rave) for the stars in common, and find similar offsets.

scholarly journals Inflection point in the power spectrum of stellar brightness variations

2020 ◽  
Vol 642 ◽  
pp. A225
Author(s):  
E. M. Amazo-Gómez ◽  
A. I. Shapiro ◽  
S. K. Solanki ◽  
G. Kopp ◽  
M. Oshagh ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Inflection Point ◽  
Active Regions ◽  
Light Curves ◽  
The Sun ◽  
Stellar Rotation ◽  
Rotation Periods ◽  
Active Stars ◽  
Effective Temperatures

Context. Stellar rotation periods can be determined by observing brightness variations caused by active magnetic regions transiting visible stellar disk as the star rotates. Successful stellar photometric surveys stemming from the Kepler and TESS observations have led to the determination of rotation periods in tens of thousands of young and active stars. However, there is still a lack of information on the rotation periods of older and less active stars like the Sun. The irregular temporal profiles of light curves caused by the decay times of active regions, which are comparable to, or even shorter than, stellar rotation periods, in combination with the random emergence of active regions make period determination for such stars very difficult. Aims. We tested the performance of a new method for the determination of stellar rotation periods against stars with previously determined rotation periods. The method is based on calculating the gradient of the power spectrum (GPS) and identifying the position of the inflection point (i.e. point with the highest gradient). The GPS method is specifically aimed at determining rotation periods of low-activity stars like the Sun. Methods. We applied the GPS method to 1047 Sun-like stars observed by the Kepler telescope. We considered two stellar samples individually: one with near-solar rotation periods (24–27.4 d) and a broad range of effective temperatures (5000–6000 K) and the other with near-solar effective temperatures (5700–5900 K) and a broad range of rotation periods (15–40 d). Results. We show that the GPS method returns precise values for stellar rotation periods. Furthermore, it allows us to constrain the ratio between facular and spot areas of active regions at the moment of their emergence. We also show that the relative facular area decreases with the stellar rotation rate. Conclusions. Our results suggest that the GPS method can be successfully applied to retrieve the periods of stars with both regular and non-regular light curves.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

A Search for Dyson Spheres around Late-Type Stars in the Solar Neighborhood II

1997 ◽  
Vol 161 ◽  
pp. 707-709 ◽  
Author(s):  
Jun Jugaku ◽  
Shiro Nishimura
Keyword(s):  
Solar Neighborhood ◽  
The Sun ◽  
Late Type ◽  
Solar Type

AbstractWe continued our search for partial (incomplete) Dyson spheres associated with 50 solar-type stars (spectral classes F, G, and K) within 25 pc of the Sun. No candidate objects were found.

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