Science with a small two-band UV-photometry mission II: Observations of stars and stellar systems

We outline the impact of a small two-band UV-photometry satellite mission on the field of stellar physics, magnetospheres of stars, binaries, stellar clusters, interstellar matter, and exoplanets. On specific examples of different types of stars and stellar systems, we discuss particular requirements for such satellite missions in terms of specific mission parameters such as bandpass, precision, cadence, and mission duration. We show that such a mission may provide crucial data not only for hot stars that emit most of their light in UV, but also for cool stars, where UV traces their activity. This is important, for instance, for exoplanetary studies, because the level of stellar activity influences habitability. While the main asset of the two-band UV mission rests in time-domain astronomy, an example of open clusters proves that such a mission would be important also for the study of stellar populations. Properties of the interstellar dust are best explored when combining optical and IR information with observations in UV. It is well known that dust absorbs UV radiation efficiently. Consequently, we outline how such a UV mission can be used to detect eclipses of sufficiently hot stars by various dusty objects and study disks, rings, clouds, disintegrating exoplanets or exoasteroids. Furthermore, UV radiation can be used to study the cooling of neutron stars providing information about the extreme states of matter in the interiors of neutron stars and used for mapping heated spots on their surfaces.Comment: Submitted to Space Science Review

Study of Eclipsing Binary and Multiple Systems in OB Associations IV: Cas OB6 Member DN Cas

An early-type, massive, short-period (P-orb = 2(d).310951) eclipsing spectroscopic binary DN Cas has been re-visited with new spectral and photometric data. The masses and radii of the components have been obtained as M-1 = 19.04 +/- 0.07M circle dot, M-2 = 13.73 +/- 0.05M circle dot and R-1 = 7.22 +/- 0.06R circle dot, R-2 = 5.79 +/- 0.06 R circle dot, respectively. Both components present synchronous rotation (V-rot1 = 160 km s(-1), V-rot2 = 130 km s(-1)) with their orbit. Orbital period analysis yielded a physically bound additional component in the system with a minimum mass of M-3 = 0.88M circle dot orbiting in an eccentric orbit (e = 0.37 +/- 0.2) with an orbital period of P-12 = 42 +/- 9 yr. High precision absolute parameters of the system allowed us to derive a distance to DN Cas as 1.7 +/- 0.2 kpc which locates the system within the borders of the Cas OB6 association (d = 1.8 kpc). The space velocities and the age of DN Cas are in agreement with those of Cas OB6. The age of DN Cas (t = 3-5 Myr) is found to be 1-2 Myr older than the embedded clusters (IC 1795, IC 1805, and IC 1848) in the Cas OB6 association, which implies a sequential star formation in the association

V2107 Cyg: A Young Cyg OB1 Member Binary System With A β Cep Type Pulsating Component

V2107 Cyg is located in the direction of Cyg OB1 stellar association. The eclipsing system consists of an early-B primary and a late-B type secondary component contributing about 6% of the total light. Line profile variability and photometry suggest strongly it is a β Cep type non-radial pulsator. A signature of the faint secondary component is for the first time identified through spectra disentangling

Interrelated main-sequence mass-luminosity, mass-radius, and mass-effective temperature relations

Absolute parameters of 509 main-sequence stars selected from the components of detached eclipsing spectroscopic binaries in the solar neighbourhood are used to study mass-luminosity, mass-radius, and mass-effective temperature relations (MLR, MRR, and MTR). The MLR function is found better if expressed by a six-piece classical MLR (L proportional to M-alpha) rather than a fifth or a sixth degree polynomial within the mass range of 0.179 1.5M(circle dot). The missing part of the MRR is computed from the MLR and MTR, while the missing part of the MTR is computed from the MLR and MRR. As a result, we have interrelated the MLR, MRR, and MTR, which are useful in determining the typical absolute physical parameters of main-sequence stars of given masses. These functions are also useful to estimate typical absolute physical parameters from typical T-eff values. Thus, we were able to estimate the typical absolute physical parameters of main-sequence stars observed in the Sejong Open cluster Survey, based on that survey's published values for T-eff. Since typical absolute physical parameters of main-sequence stars cannot normally be determined in such photometric surveys, the interrelated functions are shown to be useful to compute such missing parameters from similar surveys

Long-term, orbital, and rapid variations of the Be star V923 Aql = HD 183656

We present the latest results of a long-term observational project aimed at observing, collecting from the literature, and homogenising the light, colour, and spectral variations of the well-known emission-line Be star V923 Aql. Our analysis of these parameters confirms that all of the observables exhibit cyclic changes with variable cycle length between about 1800 and 3000 days, so far documented for seven consecutive cycles. We show that these variations can be qualitatively understood within the framework of the model of one-armed oscillation of the circumstellar disk, with a wave of increased density and prograde revolution in space. We confirm the binary nature of the object with a 214.716 day period and estimate the probable system properties. We also confirm the presence of rapid light, and likely also spectral changes. However, we cannot provide any firm conclusions regarding their nature. A quantitative modelling study of long-term changes is planned as a follow-up to this work.Comment: 21 pages, 13 Figures, Astronomy and Astrophysics (in press

Catalogue of Algol type binary stars

A catalogue of (411) Algol-type (semi-detached) binary stars is presented in the form of five separate tables of information. The catalogue has developed from an earlier version by including more recent information and an improved layout. A sixth table lists (1872) candidate Algols, about which fewer details are known at present. Some issues relating to the classification and interpretation of Algol-like binaries are also discussed