scholarly journals Circular Polarimetry of AM Herculis

1983 ◽  
Vol 72 ◽  
pp. 207-210
Author(s):  
V. Piirola ◽  
O. Vilhu ◽  
I. Tuominen
Keyword(s):  
Circular Polarization ◽  
Magnetic Axis ◽  
Light Curves ◽  
Short Term ◽  
Probable Explanation ◽  
Photometric Observations ◽  
Peak Value

ABSTRACTCircular polarimetry in the red and simultaneous photometric observations in the UBVRI bands during the period June 1-3, 1981, are discussed. The peak value of negative circular polarization PV ~ -15 % is stronger than observed in 1976-79. Variations in the shape of the polarization and light curves occur from night to night. The positive crossover and reversal of the sign of the circular polarization are only marginal. A probable explanation of the short term variations seems to be the changing shape and position of the accretion columns with respect to the magnetic axis

scholarly journals A Spectroscopic and Photometric Study of the Shell Star EW Lac

2000 ◽  
Vol 175 ◽  
pp. 554-557
Author(s):  
Huilai Cao ◽  
Zhongwei Li ◽  
Lin Huang ◽  
Yulian Guo
Keyword(s):  
Active Phase ◽  
Anomalous Behavior ◽  
Absorption Lines ◽  
Photometric Study ◽  
Short Term ◽  
Photometric Observations ◽  
Shell Star

AbstractWe report on combined spectroscopic and photometric observations of EW Lac during its outburst of 1983. At this time the star’s Hα and Hβ lines showed strong doubled-peaked emission profiles which were variable with time. UBV photometry exhibited a long-term and frequent erratic short-term variations. The amplitude of U, B and V variations reached about 0.3 magnitude on October 15, 1983. Both Hβ emission and the structure of the shell absorption lines of the star also displayed anomalous behavior in 1983. It is evident that this star was in a strong active phase at that time.

scholarly journals Optical photometric variable stars towards Cygnus OB7

2019 ◽  
Vol 487 (2) ◽  
pp. 1765-1776 ◽  
Author(s):  
Somnath Dutta ◽  
Soumen Mondal ◽  
Santosh Joshi ◽  
Ramkrishna Das
Keyword(s):  
Variable Stars ◽  
T Tauri Stars ◽  
Light Curves ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Rates ◽  
T Tauri ◽  
Photometric Observations ◽  
Sky Survey ◽  
Magnitude Diagram

ABSTRACT We present optical I-band light curves of the stars towards a star-forming region Cygnus OB7 from 17-night photometric observations. The light curves are generated from a total of 381 image frames with very good photometric precision. From the light curves of 1900 stars and their periodogram analyses, we detect 31 candidate variables including five previously identified. 14 out of 31 objects are periodic and exhibit the rotation rates in the range of 0.15–11.60 d. We characterize those candidate variables using optical/infrared colour–colour diagram and colour–magnitude diagram (CMD). From spectral indices of the candidate variables, it turns out that four are probably Classical T-Tauri stars (CTTSs), rest remain unclassified from present data, they are possibly field stars or discless pre-main-sequence stars towards the region. Based on their location on the various CMDs, the ages of two T Tauri Stars were estimated to be ∼5 Myr. The light curves indicate at least five of the periodic variables are eclipsing systems. The spatial distribution of young variable candidates on Planck 857 GHz (350 $\mu$m) and 2MASS (Two Micron All Sky Survey) Ks images suggest that at least two of the CTTSs are part of the active star-forming cloud Lynds 1003.

scholarly journals Optical Short-Term Variability in the X-Ray-Selected BL Lac Object IE 0317+186 and the Radio-Selected BL Lac Object ON231

1989 ◽  
Vol 134 ◽  
pp. 108-109
Author(s):  
F.Z. Cheng ◽  
J.F. Lu ◽  
G.Z. Xie ◽  
K.H. Li ◽  
Z.L. Li ◽  
...  
Keyword(s):  
Light Curves ◽  
Optical Monitoring ◽  
National Observatory ◽  
Image System ◽  
Short Term ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Ccd Image ◽  
Short Term Variability

In order to compare X-ray-selected BL Lac objects with radio-selected BL Lac objects, we have carried out optical monitoring of some of these objects for about three years at Yunnan Observatory in China. All observations have been made with a CCD-image system at the f/13.3 Cassegrain focus of the 102-cm RCC telescope. The CCD-image system was developed by Ye et al. in Kitt Peak National Observatory of USA (Ye et al., 1985). The filters used were as follows: B-GG385(2mm)+BG12(1mm)+BG18(1mm), V-GG495(2mm)+BG18(2mm). After observing many times, more complete light curves have obtained for the X-ray-selected BL Lac object IE 0317+186 and the radio-selected BL Lac object ON 231, respectively(Fig 1 and Fig 2). Fig 1 shows that IE 0317+186 has a characteristic timescale of about 4.5hours with an amplitudes of ΔV≃0.65 mag. Fig 2 indicates that a timescale of short-term variability in ON 231 is about 70 min with an amplitudes of ΔB≃0.8 mag.

scholarly journals A photometric and spectroscopic study of R Coronae Borealis stars in the LMC

1991 ◽  
Vol 148 ◽  
pp. 351-352
Author(s):  
W. A. Lawson ◽  
P. L. Cottrell ◽  
K. R. Pollard
Keyword(s):  
High Resolution ◽  
Spectroscopic Study ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Light Curves ◽  
Photometric Observations ◽  
R Coronae Borealis Stars

Over the last several years we have obtained photometric observations of the four suspected (W Men, HV 5637, HV 12671, HV 12842) R Coronae Borealis (RCB) stars in the Large Magellanic Cloud (LMC). Fourier analyses of the light curves has revealed some periodicity in HV 12842, where there appear to be at least two closely spaced periods of 55 and 60 d. High resolution spectra of HV 12842, obtained with the Ango-Australian Telescope (AAT), indicate that it has similar atmospheric properties to a number of warmer galactic RCB and hydrogen-deficient Carbon (HdC) stars, e.g. R CrB, RY Sgr and XX Cam.

Short-Term Spectral Variability of γ^{2} Velorum. Photometric Observations

1974 ◽  
Vol 187 ◽  
pp. L31 ◽  
Author(s):  
A. Sanyal ◽  
W. Weller ◽  
S. Jeffers
Keyword(s):  
Spectral Variability ◽  
Short Term ◽  
Photometric Observations

scholarly journals Surface Imaging of El Eri

1991 ◽  
Vol 130 ◽  
pp. 321-325 ◽  
Author(s):  
T. Hackman ◽  
N.E. Piskunov ◽  
M. Poutanen ◽  
K.G. Strassmeier ◽  
I. Tuominen
Keyword(s):  
Temperature Distribution ◽  
Imaging Technique ◽  
Light Curves ◽  
Surface Imaging ◽  
Photometric Observations ◽  
Temperature Maps

AbstractWe present maps of the temperature distribution on the spotted RS CVn-type binary EI Eri (HD 26337), obtained by means of the surface imaging technique described in the Colloquium (Piskunov, 1991). Images were calculated for two separate lines for two epochs of observation. For one epoch we also calculated an image using a blend of several lines. The reliability of the maps is confirmed by comparing the simultaneous photometric observations with the light curves calculated from the temperature maps.

Study of Pulsations in the Nova-like Variable KR Aur and the Intermediate Polar BG CMi

1991 ◽  
Vol 9 (2) ◽  
pp. 279-280
Author(s):  
J. Singh ◽  
P. C. Agrawal ◽  
M. V. K. Apparao ◽  
R. K. Manchanda ◽  
P. Vivekananda Rao ◽  
...  
Keyword(s):  
Neutron Star ◽  
White Dwarf ◽  
Accretion Disc ◽  
Light Curves ◽  
Pulsation Period ◽  
Variable Amplitude ◽  
X Ray ◽  
Photometric Observations ◽  
The Times ◽  
Made In

AbstractFast photometric observations of a nova-like variable KR Aurigae and the intermediate polar BG CMi (3A0729+103) were made in the B and U bands during 1984–89 to study pulsations in them. The light curves of KR Aur show large amplitude quasi-periodic pulsations with periods in the range 500–800s which can be ascribed to inhomogeneities in the accretion disc. The light curves of the X-ray emitting intermediate polar BG CMi show variable amplitude pulsations with 913s period. From the times of maxima of the pulsations obtained from observations over the period 1984–1989, the pulsation period is derived to be 0.010572966 ± 8 days and the spin-up rate to be (−5.7 ± 0.5) × 10−11 ss−1. The spin-up rate is consistent with the pulsating source being a white dwarf and not a neutron star.

scholarly journals X-ray Timing Studies of GRS 1915+105

1998 ◽  
Vol 188 ◽  
pp. 394-395
Author(s):  
B. Paul ◽  
P. C. Agrawal ◽  
A. R. Rao ◽  
M. N. Vahia ◽  
J. S. Yadav ◽  
...  
Keyword(s):  
Power Density ◽  
Light Curves ◽  
Energy Bands ◽  
X Ray ◽  
Photometric Observations ◽  
Different Types

We have made photometric observations of the galactic superluminal jet source GRS 1915+105 in the energy bands of 2-6 and 6-18 keV during 1997 June 12-29 and August 8-10. During our observations, different types of very intense, quasi-regular X-ray bursts have been observed from this source. We present here the light curves and the power density spectra of our observation of this source in its bright state.

Recent UBVR Photometry of Symbiotic Stars

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
A. Skopal ◽  
M. Vaňko ◽  
T. Pribulla ◽  
D. Chochol
Keyword(s):  
Light Curve ◽  
Active Phase ◽  
Symbiotic Stars ◽  
Short Term ◽  
Quiescent Phase ◽  
Photometric Observations ◽  
Made In

AbstractWe present recent photometric observations of Z And, BF Cyg, and AX Per made in the standard Johnson UBVR system. The main characteristics of their light behavior can be summarized as follows: Z And: our observations cover the recent active phase, from its maximum in 2000 December to the latest measurements (2003 September). BF Cyg: the minimum of the recent wave in the star’s brightness was the deepest ever observed; in 2003 February a short-term flare developed in the light curve. AX Per: from 1995 October the light curve displays signatures of a quiescent phase of the star; in 2003 May a 0.5 mag flare was detected.

scholarly journals Photometric and H-Alpha Variability in Some Be Stars

1987 ◽  
Vol 92 ◽  
pp. 101-103
Author(s):  
S. Catalano ◽  
G. Umana
Keyword(s):  
Magnetic Fields ◽  
Time Scales ◽  
Time Scale ◽  
Small Amplitude ◽  
Rotation Period ◽  
Light Curves ◽  
Radial Pulsation ◽  
Be Stars ◽  
Relative Movement ◽  
Short Term

Short-term variations, typically with small amplitude (Δm < 0.1 mag.), time-scales of hours or near one day and in many cases correlated with the rotation period have been found to be commonplace among Be stars (see Harmanec and Pavlovski 1983 for review and papers). Radial and non-radial pulsation modes have been proposed to explain this variability. However, the light curves are often double-peaked, at first suggesting the stars may have large organized dipole magnetic fields and spots not unlike those in the Ap or Bp stars (Harmanec 1983). These rotationally modulated variations are not stable, and seem to vary in both amplitude and period in the sense that intervals with well defined light curves alternate with intervals when variations are absent. This phenomenon is very reminiscent of formation and apparent relative movement in longitude of spots (groups) in some RS CVn binaries (Catalano 1983, Rodono 1986), but on a much more rapid time scale.

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