A photometric study of three star fields in the southern region of M33

The 2 m RCC telescope of the Rozhen National Observatory (Bulgaria) was used to obtain the colour-magnitude and colour-colour diagrams of OB110 and OB112 associations which form the largest star grouping in the southern region of M33. The stars withV andU20.4 andB21 were measured. TheV magnitude, the coloursB - V, U - B and the respective identification charts are given. This allowed to construct the luminosity function of OB110+OB112. The group has an integrated magnitudeM _VT=–11.8 which is by 0 ^m .5 fainter than OB78 (M31). The mean absorption and the foreground were examined as well.     

A photometric study of 11 massive stars in the Magellanic Clouds

We present and discuss V BLUW photometry of eleven massive stars in the Magellanic Clouds: the SMC stars AzV121, AzV136 = HD5277 = R10, AzV197, AzV310 = R26 and AzV 369; the LMC stars GV80 = HD32034 = R62, GV91 = HDE 268 819, GV346 = HDE 269661 = R111, GV352 = HDE 269697, GV423 = HDE 269953 = R150 and GV460 = HDE 270111. Only one G0 Ia SMC supergiant is found to be variable, whereas all members of the LMC sample show definite variability. We find that roughly above M /M_⊙ = 25, supergiants become photometrically unstable. The reddening‐independent metal‐index [B –L ] is used to investigate the metallicity of the late‐type supergiants in both galaxies relative to similar supergiants in the solar neighbourhood. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A new photometric study of T Tauri stars in the infrared

We have compiled infrared photometric data from the literature of practically all T Tauri stars found up to date including 444 classical T Tauri stars (CTTSs), 1698 weak-line T Tauri stars (WTTSs) and 1258 not classified T Tauri stars (3400 in total) in addition to 196 post-T Tauri stars (PTTSs). From this data bank we extract the infrared characteristics of the different groups and discuss different origins of the infrared radiation. The observational data are taken from the AKARI, IRAS, WISE and 2MASS missions. We show that in the wavelength range 1–140 μm, all T Tauri stars have infrared excesses. CTTSs have more infrared excess than WTTSs, while PTTSs have little or no infrared excess. We found that in the 1–3 μm wavelength range the infrared emission of T Tauri stars is mainly due to thermal radiation from the photosphere and hot dust grains from circumstellar envelopes. In the 3–140 μm wavelength range the infrared emission of T Tauri stars is mainly due to radiation from dusty/gaseous disks surrounding the stars. In addition, we also make a comparison between T Tauri stars and Herbig AeBe stars (HAeBe). There are some differences between these two kinds of objects in that for HAeBe stars the infrared radiation as a rule originates in dusty/gaseous disks in the 1–3 μm wavelength range, while in the range 3–12 μm it is possibly due to PAH emission for about half of HAeBe stars. In other wavelength ranges both kinds of stars have similar infrared characteristics indicating emission from dusty/gaseous disks.     

Distribution of luminous blue stars in M33

M₃₃ luminous stars with M_V ≲ -7 and U--B < o are selected in this paper. The spatial distribution of the stars shows a good agrement with the associations and HII regions. However HII regions are absent in the three youngest associations in M₃₃ (t ≈ 5 ÷ 7 × 10yr). It is supposed that the true distance modulus of M₃₃ derived from the brightest blue stars is 24.2. An age gradient across the arms is absent. The spiral arms outlined by the luminous stars differ form those in M₃₁. They are diffuse and wide. The multiarm features of M₃₃ support the stochastic self-propagating model.     

Spectrophotometric study of four bright Be stars

The spectrophotometric observations of four Be stars and one normal B-type star are reported. The continuum energy distribution data of these stars are presented in the wavelength range of 3200–8000 Å. The observations are compared with synthetic models to estimate effective temperature and to examine the behaviour of the circumstellar envelope of Be stars on their continuum energy distributions. The excess emission from the envelope affects the continua of the Be stars HR 1786 and HR 1910 strongly in the near-ultraviolet and near-infrared regions.     

A new photometric study of Herbig Ae/Be stars in the infrared

In this paper we collected almost all HAeBe stars known so far (253 sources in total) to photometrically study their infrared properties. The 2MASS, WISE, IRAS and AKARI data are employed to make analyses. It is shown from several two-color diagrams that from 1 µm to 60 µm infrared radiations from circumstellar disks with the power law distribution play a very important role for infrared excesses which are much larger than that for ordinary Be stars. In the WISE two-color diagram, (W2–W3) vs. (W1–W2), some sources show thermal emissions probably due to dust surrounded and enhanced PAH features at 3.3 and 11.3 µm. In the wavelength longer than 60 µm infrared radiations are not so influenced by the circumstellar disk, but mainly from the ISM surrounded.     

A new infrared photometric study of hydrogen-deficient carbon stars,R CrB stars and extreme helium stars in our galaxy

We have collected almost all HdC, RCB and EHe stars up to date to investigate their infrared properties, in particular, their radiation mechanisms in the infrared, using the observational data from 2MASS, WISE and IRAS missions. Because HdC stars, RCB stars and EHe stars all belong to the category of extremely hydrogen-deficient stars and they definitely have some evolutionary connections.It is found from this paper that all RCB stars have infrared excesse in the wavelength region from the near infrared to the far infrared covered by 2MASS, WISE and IRAS due to dust while almost all HdC stars and EHe stars have no or little infrared excess.From 2MASS, WISE and IRAS two-color diagrams, it is also found that the majority of these three kinds of stars are around the power law distributions in the near infrared possibly indicative of their infrared radiations from the warm dust in the disk-like envelope. It is also found that in the mid- and far infrared regions some stars are around the power law distribution perhaps due to dust from disk-like envelope while some stars are around the blackbody distribution maybe due to the cold and extended nebulosity nearby.     

UBV photometry of bright stars in the spiral arm S5 of M31

A photometric study inUBV of about 1000 bright stars outside and inside associations in S5 spiral arm is presented briefly. Characteristics of the associations (such as absorption, age and brightest stars are compared with the same characteristics of the associations in S4 spiral arm of M31, as well as in M33) are discussed.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Spectrophotometry of bright Be stars

We present new measurements of the distribution of energy in the continuum for eight Be stars in the optical region (3200-7600 Å). The effective temperatures of these stars have been estimated from their observed fluxes. It is found that, in general, pole-on stars show near-infrared excess emission. It is interesting to note that the Balmer jumps for stars having an infrared excess are systematically smaller than for those lacking the infrared excess.Variability of ultraviolet and infrared excess emissions in these stars has been discussed. The stars 59 Cyg, 66 Cyg, 28 CMa, and 27 CMa show large variations in their continuum at ultraviolet (UV) and infrared (IR) regions.     

UBV stellar photometry of bright stars in GC M5 – II. Physical parameters of horizontal branch stars

The physical parameters of the stars in the central region of the globular cluster M5 (NGC 5904) were determined from UBV photometry using Kurucz's synthetic flux distributions and some empirical relations. It is found that the bluest horizontal branch (HB) stars have higher luminosities than predicted by canonical zero-age horizontal branch models. Parameters of the mass distribution on the HB stars are determined. It is shown that the gap in the blue HB previously reported by Markov et al. in Paper I is probably a statistical fluctuation.     

A catalogue of stars suspected of bright active regions

We present a catalogue of field stars across the HR diagram suspected of bright active regions in their atmospheres.We aim at developing the first version of a database of active stars with bright regions (bright spots). Using a variety of databases and the internet we found and gathered all relevant archival data starting about 1973 and being important for developing such a catalogue. We found that the phenomenon starspot is now common to a variety of spectral type and luminosity classes. Our primary goal was to identify active solar and late type stars suspicious of bright active regions but the search offers expanded results including young T Tauri stars, eclipsing binaries with equal or mixed spectral types components (Algols,WUMa stars) and in some cases other types of objects. Moreover, the light curves analyses for eclipsing binaries offer reliable estimates for spot properties and it was found that 20% of binaries in the catalogue had a spot located near the L point (neck zone). At present, the catalogue consists of 134 stars and overall characteristics for them are organised in several files in ASCII format. The catalogue is electronically available (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The brightest blue stars in M33 galaxy as unresolved star groups

The brightest blue stars in the M33 galaxy have peculiar images. A method to resolve them into components was applied. The brightest members stars atV15–16 mag were recognized as multiple ones. Some stars up toV=17 mag have multiple structures, too. The image of the brightest blue stars consist of two or more components and probably some of them, in fact, resemble dense stellar groups such of R 136 in 30 Dor.     

Comparison of three catalogues of absolute proper motions of stars in the M33 field

Comparing absolute proper motions of stars obtained by different methods from observations with the Tautenburg Schmidt telescope (134/200/400), the Kiev long focus astrograph (40/550) and the Pulkovo normal astrograph (33/350) the external accuracy of the Tautenburg absolute proper motions was examined. It agrees well with the Tautenburg internal accuracy which is known from earlier investigations as 0″.7 per century. That accuracy was now achieved for all AGK3 stars in the M33 field including the bright stars from 7^m to 10^m.     

Calibrations for B-type stars in the Geneva photometric system

The Geneva seven-colour photometric system has been applied for almost four decades. Its data bank presently contains 345 000 measurements of 47 600 stars of all types. About 40% of the latter are of types O, B and first A. The light of these bright and massive stars is practically without exception extinguished by interstellar dust. Here, we describe various calibrations made in a three-dimensional orthogonal reddening-free representation of the system, optimised for B-stars, and that separates temperature and gravity effects. Central to all calibrations lies the empirical determination of the intrinsic colours, described here in some detail. Comparisons with synthetic photometry are made. Calibrations for effective temperature, bolometric correction, absolute magnitude are discussed as well as correlations with MK type, standard U,B,V photometry and the Strömgren β index. The unavoidable limitations imposed upon photometry by undetected causes of scatter, such as in binary systems, are evaluated. Open questions and future prospects are mentioned.     

An excess of very bright stars in the inner bulge

From an analysis of the stars remaining in central regions of the Galaxy after subtracting those belonging to the disc and the bulge, we deduce that the inner bulge must have an extra young population with respect to the rest of the bulge. It is shown that there is a higher ratio of very bright stars in the central bulge than there is in the outer bulge. This is interpreted as being an additional young component due to the presence of star formation regions near the Galactic Centre which is absent in the outer bulge.     

Near-ultraviolet observation of four bright Mn stars

Near-ultraviolet spectra, obtained with the ESRO TD-1A/S59 experiment, of the four Mn stars β Tau, γ Crv, α And, and μ Lep and six normal stars are compared. The normal stars show good agreement with synthetic spectra. The Mn stars have spectra which become hotter at shorter wavelengths. They also show strong Mnii lines and weak Mgii lines. A time-variation for Tiii λ 2828 was noted in γ Crv and α And.