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Optical and X-ray Behavior of the High Mass X-ray Transient A0535+26/HDE245770 in 2014

Giovannelli F., Bisnovatyi-Kogan G. S., Bruni I., Corfini G., Martinelli F., Rossi C.

Acta Astronomica

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2015

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Vol. 65, No. 1

107--116

EN

The optical behavior of the Be star in the high-mass X-ray transient A0535+26/HDE245770 shows that at periastron the luminosity is typically enhanced by 0.02 mag to a few tenths mag, and the X-ray outburst occurs eight days after the periastron. Indeed, at the periastron an increase of the mass flux occurs. This sort of flush reaches the external part of the temporary accretion disk around the neutron star and moves to the hot central parts of the accretion disk and the neutron star's surface. The time necessary for this process is dependent on the turbulent viscosity in the accretion disk. In this paper we will show the behavior of this system in optical band around the predicted periastron passages in 2014, by using the ephemeris - JDopt-outb = JD0(2 444 944)±n(111.0±0.4) days - that we used to schedule our spectroscopic and photometric optical observations. Spectroscopic unusual activity detected in the Balmer lines and the enhancement in the emission in B, V, and R bands around the 106th periastron passage, and in V-band around the 108th periastron passage after the "zero event" 811205-E at JD 2 444 944, and the subsequent X-ray events definitively demonstrate the existence of a ≈8-day delay between optical and X-ray flares.

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A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. VI. NGC 6910

Kołaczkowski Z., Pigulski A., Kopacki G., Michalska G.

Acta Astronomica

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2004

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Vol. 54, No. 1

33--55

EN

We present results of variability search in the field of the young open cluster NGC 6910. We found four &beta Cep-type stars in the cluster, which makes it rather exceptional among the northern clusters observed in our project. Two of these &beta Cep stars show three modes with amplitudes above the detection level, in the remaining two we detect single modes. We discuss the possibility that the large number of &beta Cep stars in NGC 6910 is due to higher metallicity of the cluster. In addition, we found four other variables, one ellipsoidal or eclipsing binary and three that show irregular variations. The latter three stars have Hα in emission. We also provide VIC photometry for 139 stars down to V=16.6 mag and Hα photometry for 73 stars. Using this photometry we estimate the cluster age to be equal to 6±2 Myr, and the distance modulus, 11.0±0.3 mag. The reddening is high and variable across the cluster. In terms of the E(V-IC) color-excess it amounts to 1.25-1.7 mag, corresponding to E(B-V) between 1.0 mag and 1.4 mag. The average reddening in the central field is E(V-IC)=1.47±0.04 mag.

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Erratum: A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. III. NGC 6823

Pigulski A., Kołaczkowski Z., Kopacki G.

Acta Astronomica

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2000

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Vol. 50, No. 2

278

EN

In the paper ”A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. III. NGC 6823” (Acta Astron., 50, p. 113) the entries in the last column of Table 2 (times of maximum light) are too large by 1000 days. The correct Table 2 follows:

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A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. III. NGC 6823

Pigulski A., Kołaczkowski Z., Kopacki G.

Acta Astronomica

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2000

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Vol. 50, No. 1

113--132

EN

We present the results of variability search in the field of a very young open cluster NGC 6823. Two δ Sct stars, still at the pre-main sequence (PMS) stage of evolution, were found. These objects could be used for future testing of the evolutionary period changes in this class of variable stars. In addition, we found 13 other variables including a bright cluster eclipsing binary and an SPB candidate. A few other variables could be PMS stars of the UX Ori type. The Hα photometry, which we made for 69 brightest stars, revealed only one object with strong emission, discovered recently by the photographic methods. Two other stars announced to have Hα emission, do not show any evidence for its presence. For a number of stars in the search field, we also provide the BV(RI)C photometry. We explain how the distribution of absorbing matter along the line of sight results in the unusual morphology of the cluster color-magnitude (CM) diagram. The dereddened CM diagram is used in the calculation of the extinction map for the observed field, in which the E(R-I)C color excess varies from 0.54 to 0.72 mag, with the average value equal to 0.62 mag. It is also shown that all cluster stars with spectral types later than A0 are PMS objects. We use these stars to estimate the cluster age: 3±1 Myr. Using the cluster CM diagram, we compare and discuss the position of the two discovered δ Sct stars with respect to the theoretical instability strip for PMS stars of this type.