scholarly journals Studies of variability of circumstellar H2O masers

1987 ◽  
Vol 122 ◽  
pp. 267-268
Author(s):  
G. M. Rudnitskij
Keyword(s):  
Near Infrared ◽  
Variable Stars ◽  
Lebedev Physical Institute ◽  
Phase 0 ◽  
Maser Line ◽  
Type Variable ◽  
Academy Of Sciences ◽  
Maser Radio ◽  
Observational Program ◽  
Infrared Brightness

From March 1980 to December 1983, the author took part in regular observations of variability of maser radio emission in the H2O line at 22 GHz. The observations were carried out at the 22-meter radio telescope of the P. Lebedev Physical Institute (USSR Academy of Sciences) in Pushchino (Moscow Region). The interval between consecutive observational sessions was usually 1.5–2 months. The observational program included 21 late-type variable stars (Miras and SRs): R Aql, RR Aql, RT Aql, SY Aql, U Aur, NV Aur, RX Boo, VY CMa, S CrB, KY Cyg, NML Cyg, U Her, W Hya, X Hya, R Leo, U Lyn, U Ori, UU Peg, VX Sgr, RS Vir, RT Vir. The results for eight stars ending June 1982 were published by Berulis et alt (1983). A comparison was made between the time dependences of the H2O line radio flux F and the curves of visual and near-infrared brightness of the stars. Miras (R Aql, R Leo, U Ori, U Aur), as a rule, have a rise in F connected with the visual maximum (phase 0), the maximum F occurring at phases 0.1–0.2 (see figure for an example). Not all visual maxima (only one out of each two or three) are accompanied by H2O flares. This Miras! behaviour was also noted earlier in the H2O line by Berulis et al. (1984), Gómez Balboa and Lépine (1986), as well as in the SiO maser line v=1, J=2−1 by Nyman and Olofsson (1986).

scholarly journals Multiwavelength Studies of Mira Ceti-type Variable Stars

1999 ◽  
Vol 191 ◽  
pp. 201-206 ◽  
Author(s):  
V.F. Esipov ◽  
M.I. Pashchenko ◽  
G.M. Rudnitskij ◽  
M.V. Kozin ◽  
E.E. Lekht ◽  
...  
Keyword(s):  
Time Series ◽  
Emission Intensity ◽  
Variable Stars ◽  
Optical Variability ◽  
Line Flux ◽  
Maser Line ◽  
Type Variable ◽  
Hα Emission ◽  
Ceti Type ◽  
Spectral Ranges

Since 1994, observations of a sample of about 20 Mira Ceti-type and semiregular variables have been carried out in three spectral ranges: radio (H2O maser line λ = 1.35 cm), optical (spectroscopy and UBV photometry) and infrared (JHKLM photometry). Time series of the Hα emission intensity and H2O line flux, covering several periods of the stars, have been obtained. Correlation of the intensity variations of the H2O maser with optical variability in the maser stars RR Aql, U Ori, VX Sgr and others was confirmed. One of the most interesting results is the flare of the H2O maser emission in R Leo, which happened in autumn 1997, 14 months after a flare of the Hα emission.

The Nature of Boxy/Peanut Spiral Galaxies: Overview and New Results

1997 ◽  
Vol 14 (2) ◽  
pp. 146-158 ◽  
Author(s):  
M. Bureau ◽  
K. C. Freeman
Keyword(s):  
Formation Mechanism ◽  
Vertical Structure ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Spiral Galaxies ◽  
Physical Conditions ◽  
Bar Buckling ◽  
Line Imaging ◽  
Observational Program

AbstractThe formation mechanism of boxy/peanut-shaped bulges in spiral galaxies has been a problem for many years. We briefly review here the possible formation scenarios for boxy/peanut bulges, concentrating on both the bar-buckling and accretion hypotheses, and then describe an observational program aimed at testing those various theories and studying the vertical structure of edge-on bars. Our program includes optical long-slit spectroscopy, Hiline-imaging, near-infrared imaging, and multi-band optical imaging. New spectroscopic results (both optical and Hi) are presented on seven galaxies, including five boxy/peanut-bulge spirals. Based on Kuijken & Merrifield's (1995) idea for detecting edge-on bars, we argue that these observations constitute a strong case in favour of the bar-buckling mechanism for the formation of boxy/peanut-shaped bulges, but they also raise many questions and prompt for more detailed modelling to be made. The implications of the observations concerning the determination of rotation curves and of the physical conditions in bulges are also discussed.

scholarly journals Optical properties of spray pyrolysis deposited Cds:Al thin films

2015 ◽  
Vol 39 (1) ◽  
pp. 25-30 ◽  
Author(s):  
A Hasnat Rubel ◽  
J Podder
Keyword(s):  
Thin Films ◽  
Optical Properties ◽  
Spray Pyrolysis ◽  
Near Infrared ◽  
Visible Region ◽  
Cadmium Sulphide ◽  
Infrared Region ◽  
Photo Detectors ◽  
Direct Energy ◽  
Academy Of Sciences

Aluminium doped cadmium sulphide thin films were prepared on glass substrate using aqueous solution of cadmium sulphide and thiourea salts by spray pyrolysis deposition (SPD) technique. Its optical properties were analyzed as a function of doping concentration. The direct energy band-gap of Al-doped CdS films was estimated in the range of 2.25 to 2.48 eV. The optical spectra of Cd1-xAlxS ternary system exhibit high absorption near visible region and transmission throughout the near-infrared region (600 - 1200 nm). Thus so obtained hetero-junction films are suitable for fabrication of photo detectors, solar cells and other optoelectronics devices.Journal of Bangladesh Academy of Sciences, Vol. 39, No. 1, 25-30, 2015

scholarly journals Faint Standards for ZYJHK from the UKIDSS and VISTA Surveys

2020 ◽  
Vol 493 (2) ◽  
pp. 2568-2595
Author(s):  
S K Leggett ◽  
Nicholas J G Cross ◽  
Nigel C Hambly
Keyword(s):  
Near Infrared ◽  
Variable Stars ◽  
Calibration Data ◽  
Infrared Telescope ◽  
Final Sample ◽  
Sky Survey ◽  
Data Release ◽  
Deep Survey ◽  
Large Telescopes ◽  
Astrometric Data

ABSTRACT The currently defined ‘United Kingdom Infrared Telescope (UKIRT) Faint Standards’ have JHK magnitudes between 10 and 15, with Kmedian = 11.2. These stars will be too bright for the next generation of large telescopes. We have used multi-epoch observations taken as part of the UKIRT Infrared Deep Sky Survey (UKIDSS) and the Visible and Infrared Survey Telescope for Astronomy (VISTA) surveys to identify non-variable stars with JHK magnitudes in the range 16–19. The stars were selected from the UKIDSS Deep Extragalactic Survey and Ultra Deep Survey, the WFCAM calibration data (WFCAMCAL08B), the VISTA Deep Extragalactic Observations (VIDEO), and UltraVISTA. Sources selected from the near-infrared databases were paired with the Pan-STARRS Data Release 2 of optical to near-infrared photometry and the Gaia astrometric Data Release 2. Colour indices and other measurements were used to exclude sources that did not appear to be simple single stars. From an initial selection of 169 sources, we present a final sample of 81 standard stars with ZYJHK magnitudes, or a subset, each with 20 to 600 observations in each filter. The new standards have Ksmedian = 17.5. The relative photometric uncertainty for the sample is <0.006 mag and the absolute uncertainty is estimated to be ≲ 0.02 mag. The sources are distributed equatorially and are accessible from both hemispheres.

The Spectra of U Geminorum Type Variable Stars.

1943 ◽  
Vol 97 ◽  
pp. 412 ◽  
Author(s):  
C. T. Elvey ◽  
H. W. Babcock
Keyword(s):  
Variable Stars ◽  
Type Variable

scholarly journals Variable Stars in the Globular Cluster NGC 6934

1980 ◽  
Vol 85 ◽  
pp. 455-457
Author(s):  
Helen Sawyer Hogg ◽  
Amelia Wehlau
Keyword(s):  
Globular Cluster ◽  
Variable Stars ◽  
First Time ◽  
Observational Program

In the first program of direct photography with the 72-inch telescope of the Dominion Astrophysical Observatory, 1931–1934, the compact and distant globular cluster NGC 6934 in Delphinus was searched for variables for the first time by HSH. The 51 discovered were published in 1938 (Sawyer-Hogg 1938). From 1935 to 1964 the observational program was continued with the 74-inch telescope of the David Dunlap Observatory and a total of 161 plates was accumulated. In addition, six Mount Wilson plates from 1911 to 1917 were available to us.

scholarly journals Molecular Masers in Variable Stars

2002 ◽  
Vol 19 (4) ◽  
pp. 499-504 ◽  
Author(s):  
Georgij M. Rudnitskij
Keyword(s):  
Line Emission ◽  
Variable Stars ◽  
Circumstellar Envelope ◽  
Red Giants ◽  
Circumstellar Envelopes ◽  
Emission Data ◽  
Physical Mechanisms ◽  
Stellar Pulsations ◽  
Red Giant ◽  
Maser Radio

AbstractWhen a star with a mass of one to a few solar masses enters the red giant stage of its evolution, the radius of its atmosphere reaches several astronomical units. Pulsational instability is typical for this stage. Most stars become Mira-type or semiregular variables with light cycles of a few hundred days. Red giants lose mass at a rate M = 10−7−10−5M⊙ yr−1. Extensive gas–dust circumstellar envelopes form. These envelopes contain various molecular species. Some of these molecules (OH, H2O, SiO, HCN) manifest themselves in maser radio emission. Data on the H2O maser variability and its connection with the stellar brightness variations are discussed. In the H2O line circumstellar masers can be divided into ‘stable’ (showing persistent emission — R Aql, U Her, S CrB, X Hya) and ‘transient’ (appearing in the H2O line once per 10–15 stellar light cycles — R Leo, R Cas, U Aur). Physical mechanisms of the maser variability are discussed. The most probable process explaining the observed visual–H2O correlation is the influence of shock waves on the masing region. Usually it is assumed that shocks in Mira atmospheres are driven by stellar pulsations. Here an alternative explanation is proposed. If a star during its main sequence life possessed a planetary system, similar to the solar system, the planets will be embedded in a rather dense and hot medium. Effects of a planet revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. A shock produced by the supersonic motion of a planet can account for the correlated variability of the Hα line emission and H2O maser. If the planetary orbit is highly eccentric, then the connected Hα–H2O flare episodes may be explained by the periastron passage of the planet. New tasks for the upgraded ATCA are discussed.

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