We present a study of the influence of magnetically induced control of external convection in stars of different types, in particular white dwarfs, on their thermal evolution. In the work preceding ...this study, we argued that for the cooling down white dwarf stars that have exhausted the sources of thermonuclear combustion, cessation of convection by a magnetic field significantly slows down their cooling. To test this asertion, we performed an observational program to search for new highly magnetized white dwarfs. The program is described in detail in the same issue of the journal. Our observations, together with the observations of other researchers, allowed us to construct the observed luminosity function of strongly magnetized white dwarfs with stopped convection and compare it with the well-known similar luminosity function of white dwarfs with weak fields that allow effective convective heat removal from their insides. As a result of the model analysis of these functions, the hypothesis that strongly magnetized white dwarfs cool down slower than weakly magnetic ones is confirmed. The article also qualitatively examines the effect of magnetic braking of convection in solar-type stars and cool M-dwarf stars of the Main Sequence on the periodicity of their radiation activity. The geophysical aspect of the problem and the practical application of magnetic field control of the heat removal in electrically conductive media are discussed.
We present the results of observations within the program for the search for new highly magnetized white dwarfs among evolutionary old stars of this class. The program was carried out for two years ...at the 1-m telescope of the SAO RAS. As a result, new white dwarf candidates of different ages with super-strong (several megagauss, tens, hundreds of megagauss) magnetic fields were discovered. These observations, along with the observations of other authors made it possible to make a new estimate of the frequency of occurrence of magnetic white dwarfs among old stars. Our results confirm our earlier assumptions that the frequency of occurrence of far-evolved magnetic white dwarfs with magnetic fields of several megagauss or higher and with the temperatures of less than 10 000 K is at the level of 15% or higher, while the frequency of occurrence of such stars among young white dwarfs does not exceed 4–6%. This fact means that the thermal evolution of the physical properties of magnetic white dwarfs differs from the thermal evolution of their weakly magnetic counterparts.
We discuss possible relations between different constituents of interstellar clouds, such as gas atoms (Fe i), simple molecular species (CH, CN), and the carriers of the puzzling diffuse interstellar ...bands (DIBs 5780, 5797, 5850 ) as well as dust grains. We exemplify that abundances of carriers of these spectral features, revealed by the Doppler components, may be astonishingly poorly related to each other. Spectra of interstellar clouds seem to be sensitive to the changes of the environmental parameters such as density, temperature, and irradiation from nearby stars. The diffuse bands' carriers likely do not occupy the same volumes with CH, CN, or Fe i and/or are much less sensitive to the processes related to the formation/destruction of these species.
We show that the equivalent widths of the well-known interstellar Ca II H and K lines can be used to determine the distances to OB stars in our Galaxy. The equivalent widths, measured in the spectra ...of 147 early-type stars, are strongly related to the Hipparcos parallaxes of those objects. The lines fitted to the parallax-equivalent width data are given by the formulae p = 1/2.78EW(K) + 95 and p = 1/4.58EW(H) + 102, where p is in arcseconds and EW is in milliangstroms. The form of the formulae, yielding a finite parallax even for zero absorption, shows that space within -100 pc of the Sun contains very little Ca II, which is in agreement with the known dimensions of the Local Bubble. Using Ca II lines for distance determination does not require the knowledge of the absolute magnitude of the object; it is thus well suited for targets for which the absolute calibration is either not precise (OB supergiants) or not available at all (peculiar objects). We also demonstrate that neither the reddening E(B - V) nor the equivalent widths of interstellar K I and CH lines are suitable candidates for distance estimation, their relation with parallaxes being far less tight than for Ca II.
We investigate whether there are variations of the central wavelengths or the profile shapes of diffuse interstellar bands and whether these variations are caused by different physical parameters of ...translucent clouds. For this purpose we used spectra of two stars seen through two different single clouds: HD 34078 (AE Aur) and HD 73882. The wavelength displacements of the diffuse interstellar bands at 6196 Å, 6203 Å, 6376 Å, 6379 Å and 6614 Å with respect to the well known interstellar atomic and molecular lines (KI and CH) were measured. The shift is seemingly absent in the diffuse interstellar bands at 4726 Å, 4964 Å, 4763 Å, and 4780 Å. In addition the considered profiles may show (in HD 34078) extended red wings. The observed phenomena are likely related to physical parameters of intervening clouds (rotational temperatures of molecular species) and may help in the identification of the diffuse interstellar band carriers.
We report observations of four weak absorption lines of the interstellar CN A2Π-X2Σ+ (3,0) band: R1(0) 6951.8 Å, RQ21(0) 6927.3 Å, R2(1)+RQ1(1) 6926.7 Å, QR12(1)+Q1(1) 6953.6 Å, and show that they ...provide reasonable information on column densities in sightlines towards early-type stars. The (3,0) band is always very weak and thus the saturation effect is negligible, which is particularly useful for the sightlines where the near UV-range CN bands are very strong, i.e. saturated.
We present a test how far the direct, trigonometric parallax measurements and those, based on interstellar CaII H and K lines lead to distances to OB stars similar to those, based on ...spectrophotometrically determined ones. For this we use relatively nearby objects where the extinction effects are negligible. A test is based on observations of interstellar CaII H and K lines, that determine distances, in spectra of bright, nearby objects, free of extinction effects. For these objects one can find also trigonometric parallaxes. CaII H and K lines are weak in spectra of nearby stars and thus measurable only in high S/N ratio spectra. Such spectra being at our disposal also allow us to check the spectral classification of our targets and thus to comment the observed differences between distances acquired using different methods. Using four methods, we determined distances to nearly fifty B0-5 type stars, practically free of any extinction effects. We demonstrate that direct, astrometric, CaII H and K and spectrophotometric distances agree reasonably well in the absence of substantial interstellar extinction and when spectral classification is reliable. Apparently the absolute magnitude calibration, provided by Schmidt-Kaler, appears to be correct.
Eight Exoplanet Candidates in SAO Survey Yakovlev, O. Ya; Valeev, A. F.; Valyavin, G. G. ...
Astrophysical bulletin,
03/2023, Volume:
78, Issue:
1
Journal Article
Peer reviewed
Open access
We report eight new exoplanet candidates discovered at the Special Astrophysical Observatory of the Russian Academy of Sciences using the transit technique. Photometric observations were performed ...with a 50-cm robotic telescope during the second half of 2020. Transits with depths of
and periods
were detected in
–
stars. All the stars considered are dwarfs with radii
(with an uncertainty of up to
for a single star). We use simulations to estimate the candidate radii (all are greater than 1.4 times the Jovian radius), semi-major axes of their orbits (0.012–0.035 AU), and other orbital parameters. We report the transit light curves for two stars obtained in 2022 based on individual observations.
Optical absorption bands of the interstellar CN (near 3875 Å) and CH molecules (the violet and blue ones near 4300 and 3886 Å, respectively) were applied to determine the column densities of these ...two radicals in a statistically meaningful sample of 84 reddened OB stars. Equivalent widths of the major 5780 and 5797 diffuse bands (DIBs) were measured along the lines of sight toward the same stars in spectra acquired using four echelle spectrographs situated in both the northern and southern hemispheres. The mutual relation between abundances of CH and CN molecules shows a large scatter; and especially the CN molecule abundance varies strongly from cloud to cloud. The carriers of the major 5780 and 5797 DIBs seem to be spatially correlated with column densities of CH rather than of the CN molecule. This is most likely true in the case of a narrower feature: the 5797 DIB correlates with CH column density better than 5780 does. The correlations do suggest that the DIB carriers are likely hydrocarbons. They apparently occupy molecular clouds since the H2 abundance is closely related to that of methylidyne (CH), as has already been demonstrated.
—Within the program for studying the variability of slow-rotating magnetic stars, we carried out magnetic monitoring of the Ap star HD 110066 (AX CVn), the expected variability period of which was ...estimated as 13.4 yrs. Based on our measurements of the magnetic field performed with the 1-m SAO RAS telescope and the literature data, we assumed that the most likely period of this star
days; we also estimated the parameters of the oblique rotator model describing the magnetic variability of the star HD 110066. In order to determine its chemical abundance, a high-resolution spectrum with (
) was obtained using the fiber-fed spectrometer of the 6-m telescope of SAO RAS. The chemical abundance estimates completely coincided with those from the spectrum obtained with a similar resolution with the ESPaDOnS spectrometer (CFHT, Mauna Kea, Hawaii).
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