Photometric observations of supersoft sources in the LMC

ABSTRACT We present the results of our BVR-band photometric and R-band polarimetric observations of ∼40 stars in the periphery of the dark cloud CB54. From different photometric data, we estimate E(B − V) and E(J − H). After involving data from other sources, we discuss the extinction variations towards CB54. We reveal two main dust layers: a foreground, E(B − V) ≈ 0.1 mag, at ∼200 pc and an extended layer, $E(B-V) \gtrsim 0.3$ mag, at ∼1.5 kpc. CB54 belongs to the latter. Based on these results, we consider the reason for the random polarization map that we have observed for CB54. We find that the foreground is characterized by low polarization ($P \lesssim 0.5$ per cent) and a magnetic field parallel to the Galactic plane. The extended layer shows high polarization (P up to 5–7 per cent). We suggest that the field in this layer is nearly perpendicular to the Galactic plane and both layers are essentially inhomogeneous. This allows us to explain the randomness of polarization vectors around CB54 generally. The data – primarily observed by us in this work for CB54, by A. K. Sen and colleagues in previous works for three dark clouds CB3, CB25 and CB39, and by other authors for a region including the B1 cloud – are analysed to explore any correlation between polarization, the near-infrared, E(J − H), and optical, E(B − V), excesses, and the distance to the background stars. If polarization and extinction are caused by the same set of dust particles, we should expect good correlations. However, we find that, for all the clouds, the correlations are not strong.

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Diva - A Small Satellite for Global Astrometry and Photometry

Highlights of Astronomy ◽

10.1017/s1539299600022413 ◽

1998 ◽

Vol 11 (1) ◽

pp. 583-583

Author(s):

S. Röser ◽

U. Bastian ◽

K.S. de Boer ◽

E. Høg ◽

E. Schilbach ◽

...

Keyword(s):

High Precision ◽

Wavelength Range ◽

Fizeau Interferometer ◽

Proper Motions ◽

Small Satellite ◽

Short Overview ◽

Photometric Observations ◽

Photometric Measurements ◽

First Time ◽

Astronomy And Astrophysics

DIVA (Double Interferometer for Visual Astrometry) is a Fizeau interferometer on a small satellite. It will perform astrometric and photometric observations of at least 4 million stars. A launch in 2002 and a minimum mission length of 24 months are aimed at. A detailed description of the experiment can be obtained from the DIVA homepage at http://www.aip.de:8080/᷉dso/diva. An overview is given by Röser et al., 1997. The limiting magnitude of DIVA is about V = 15 for spectral types earlier than M0, but drops to about V = 17.5 for stars later than M5. Table 1 gives a short overview on DIVA’s performance. DIVA will carry out a skysurvey complete to V = 12.5. For the first time this survey will comprise precise photometry in at least 8 bands in the wavelength range from 400 to 1000 nm. DIVA will improve parallaxes by a factor of 3 compared to Hipparcos; proper motions by at least a factor of 2 and, in combination with the Hipparcos observations, by a factor of 10 for Hipparcos stars. At least 30 times asmany stars as Hipparcos will be observed, and doing this DIVA will fill the gap in observations between Hipparcos and GAIA. DIVA’s combined astrometric and photometric measurements of high precision will have important impacts on astronomy and astrophysics in the next decade.

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Asteroid collisions as origin of debris disks: Asteroid shape reconstruction from BNAO Rozhen photometry

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319009426 ◽

2019 ◽

Vol 15 (S350) ◽

pp. 451-453

Author(s):

G. Apostolovska ◽

E. Vchkova Bebekovska ◽

A. Kostov ◽

Z. Donchev

Keyword(s):

Laboratory Experiments ◽

Extrasolar Planets ◽

Shape Reconstruction ◽

Inversion Method ◽

Debris Disks ◽

Shape Parameters ◽

Zodiacal Cloud ◽

Photometric Observations ◽

Different Shapes ◽

Asteroid Surface

AbstractAs a result of collisions during their lifetimes, asteroids have a large variety of different shapes. It is believed that high velocity collisions or rotational spin-up of asteroids continuously replenish the Sun’s zodiacal cloud and debris disks around extrasolar planets (Jewitt (2010)). Knowledge of the spin and shape parameters of the asteroids is very important for understanding collision asteroid processes. Lately photometric observations of asteroids showed that variations in brightness are not accompanied by variations in colour index which indicate that the shape of the lightcurve is caused by varying illuminations of the asteroid surface rather than albedo variations over the surface. This conclusion became possible when photometric investigations were combined with laboratory experiments (Dunlap (1971)). In this article using the convex lightcurve inversion method we obtained the sense of rotation, pole solutions and preliminary shape of 901 Brunsia.

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Fast Drift-Scan CCD Imaging and Photometry with Small Telescopes: Lunar Occultations and Speckle Interferometry

International Astronomical Union Colloquium ◽

10.1017/s0252921100079148 ◽

2001 ◽

Vol 183 ◽

pp. 309-314

Author(s):

Jorge Núñez ◽

Octavi Fors

Keyword(s):

Data Analysis ◽

Speckle Interferometry ◽

Close Binary ◽

Ccd Cameras ◽

Ccd Imaging ◽

Scanning Technique ◽

Photometric Observations ◽

Drift Scan ◽

Fast Drift ◽

Year 2000

AbstractIn this paper we show how inherent features of typical CCD cameras can be used for fast (in the order of milliseconds) photometric observations (FPO), even with submeter class telescopes. This is based on a modified drift-scanning technique which we show to be advantageous for such kind of observations. In particular, we successfully carried out some lunar occultations and speckle interferometry observations using this technique. During the year 2000, we registered several occultation events. In particular, we present the occultation of SAO79031. The millisecond photometry of the event allows us subsequent data analysis for stellar diameter estimation and close binary detection. We also show an example of the application of the technique to speckle interferometry observations. Finally, we present the main characteristics of our project to build a new remotely controlled observatory near Barcelona.

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Influence of Rotation on the Stellar Parameters

International Astronomical Union Colloquium ◽

10.1017/s0252921100017668 ◽

1993 ◽

Vol 137 ◽

pp. 162-164 ◽

Cited By ~ 2

Author(s):

V. Wenske ◽

D. Schönberner

Keyword(s):

Lower Surface ◽

Equatorial Region ◽

Star Formation History ◽

Rotational Rate ◽

Visible Part ◽

Photometric Observations ◽

Formation History ◽

Inclination Angles ◽

Stellar Models ◽

Stellar Masses

For several years it has become quite common to derive stellar parameters like effective temperature, Teff, and surface acceleration, g, by means of properly calibrated photometric indices, and to use these values for the derivation of important properties of stellar aggregates (viz. ages, star formation history, distances, etc.). Photometric observations, however, fail to give informations about one important property of a star: its rotational rate!The main effect of rotation is to increase the size of the star, mainly in the equatorial region, leading to lower surface temperatures and accelerations. Since in non–spherical stars Teff and g depend on the latitude, the observed values, which are, of course, averages over the visible hemisphere, depend on the angle of inclination, i. Collins & Sonneborn (1977) utilized the rigidly rotating stellar models of Sackmann and Anand (1970) to compute emergent fluxes and photometric indices for various stellar masses, inclination angles i and rotational parameters being the break–up rotational rate. These indices, viz. C0 and β, represent then averages over the visible part of the rotally distorted stellar models. Closer inspections indicated also that emergent fluxes and line profiles of rotationally distorted stars can be matched by the predictations of standard model atmospheres to a very high accuray, even for w close to unity (Wenske 1992, Diplom Thesis).

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