Photometry of the bright stars inside and outside associations in the spiral arm S5 of the andromeda galaxy

Photometry of more than 1000 bright stars of 20 associations and some fields in its vicinity is made, usingUBV plates taken with a 2-m Ritchey-Chrétien telescope of the National Observatory at the Bulgarian Academy of Sciences with limited magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitude and colour-colour diagrams of 12 associations and 8 fields are constructed and the brightest blue and red stars colour excesses, ages, and integrated luminosities of the associations are determined. The composite diagrams for all association and nonassociation measured stars are constructed too. Inside associations bright stars as well as non-stellar objects occur more often than outside. The brightest stars in S5 are withM _v7 and do not differ considerably from the brightest ones in the spiral arm S4 of M31. Approximately the same are the absolute magnitudes of the brightest stars in our Galaxy and M33. A small difference between the brightest stars of the latter galaxy with those of M31 is possible because the stars in M33 are younger. This is in agreement with the concept that Sc galaxies (for example M33) are younger than Sb ones (for example M31). The same could be the reason for the smaller ratio of blue to red supergiants in M33 than in M31. The age estimations of the associations in S5 together with those in S4 in M31 show that they are older than the associations in M33 which is in agreement with the above mentioned concept.     

Spectroscopic and photometric characteristics of stars in the field of the cluster vdB 130

The observational data for 24 stars toward the young cluster vdB 130 are analyzed. The spectroscopic and photometric BV RIJHK observations have been carried out with the following telescopes: 6-m at the Special Astrophysical Observatory of the Russian Academy of Sciences, 60-cm at the Southern Station of the Moscow State University, and 2.5-m at the Caucasus Observatory of the Sternberg Astronomical Institute of theMoscow State University. Nine stars previously selected as cluster members have been found to belong to different subtypes of type B. A minimum color excess toward the cluster, E(B ? V) = 0.9 mag, has been revealed for the vdB 130 stars lying outside the molecular cloud. Maximum color excesses, E(B ? V) = 1.3?1.4 mag, have been found in the spectra of cluster stars 1r and 5r observed in dust blobs. Inside the cluster R _v is shown to differ from the standard one. The overwhelming majority of the remaining investigated stars belong to late types and have minor color excesses (≤0.3) typical of close distances.     

The stellar content of binary star clusters in the LMC

The bright stellar content for fifteen binary star clusters and their adjoining fields in the Large Magellanic Cloud (LMC) were studied here. Film copies of plates taken with the 1.2 U.K. Schmidt telescope were used for deriving the spectral types of the stars in the studied regions. All classified stars are brighter thanV=17.5 mag and situated in large areas around each pair and in a neighbouring field. Seven of the pairs, the brightest and most populous are young clusters (located mainly at the north part of the parent galaxy). The derived distributions of spectral types of their stars give strong evidence that each pair consists of similar stellar content with ages 0.6–8×10⁷ yr.Eight more binary star clusters were studied as well, selected among the rest of the binaries in the LMC. It is found that their stars were faint for our limit of detection so the poor statistics did not allow a comparison among the two cluster members of each pair. However the bright limit of their stars implies ages >6×10⁸ yr. Considering that these objects were randomly selected it is unlikely that all are projected pairs. So it seems that binarity in star clusters is a phenomenon (favourable in the LMC) which did not happen only once in the life of this galaxy.     

Models of pulsating low-massive yellow supergiants

The nonlinear self-excited oscillations of the envelopes of low-massive highly luminous stars are described. The parameters for these models wereM=0.8M ,M _bol=–5.5, –5.84 mag,T _eff=4500, 5000, 5500 K. The oscillations have been found to consist of the standing wave pulsation near the envelope bottom and running waves in outer layers. The ratio of the standing wave frequency _s to the average frequency of the running waves _r increases with the stellar luminosity: _s / _r =1.7 whenM _bol=–5.5 mag and _s / _r =2.4 whenM _bol=–5.84 mag. The frequency of oscillations near the photosphere is found to be in close agreement with the critical frequency for running waves. Mass loss from these stars is caused by shocks. It has been shown that agreement between FG Sge's period change observed during the last decade and the period-luminosity relation for double shell stars takes place when FG Sge's luminosity isM _bol=–5.96 mag.     

Search for HH Objects and Emission Stars in Star Formation Regions. III. PMS Stars in NGC 7129

Slitless spectroscopy is used to discover 22 emission stars in the central and northwest regions of the cluster located in the NGC 7129 nebula. 16 of them are found for the first time. This sample is essentially complete up to V 20.0. The emission stars are distributed nonuniformly over the field of the cluster and are concentrated toward its center. Photometry in the V, R, and I bands is conducted on more than a hundred stars in the cluster. This yields an average absorption coefficient A _V=1.7±0.27 for this region. Based on their positions in color diagrams for the optical and near IR ranges, most of the emission stars can be regarded as T Tau objects.     

Spectrophotometric studies of Am stars

The relationships among the various physical parameters-namely, the effective temperatures, radii and bolometric magnitudes, determined on the basis of the energy distribution curves of 25 Am stars — have been studied. Their effective temperatures are in the range of 7200 K to 9700 K; the radii, 1.5R to 2.5R ; the bolometric magnitudes, 0.75 mag. to 2.25 mag.; and the masses, 1.5M to 2.25M . The Am stars in general, appear redder than their normal counterparts, the blanketing in the blue andUV regions being the major cause. For the relatively cooler stars, the (B-V) colours are found to be less affected by blanketing. They are located in the neighbourhood of the upper edge of the zero-age Main Sequence band and show a fairly wide range in the evolutionary status among themselves. The bolometric corrections which are independent of the uncertainties in the parallax measurements, follow the same trend as that of the Ap stars, with reference to the temperature.     

A colour-agnitude diagram of the Pisces dwarf galaxy

We present B, V and R band CCD images of the dwarf galaxy LGS-3 (Pisces dwarf). About 180 stars and diffuse objects were found and processed in these frames. The colour-magnitude diagram shows a prominent red giant branch and a few blue stars only. Details of the morphological properties and colour-agnitude diagram indicate to an intermediate (between dIrr and dSph) type of LGS-3. We estimate the galaxy distance modulus to be about (m - M)₀ = 23.9 ± 0.3 mag on the basis of the tip of the red giant branch. We measured the galaxy colour to be about B–V = 0.8 mag and the linear diameter 700 pc, which is the smallest one in the Local group.     

The oldest galactic open clusters: New CCD photometry and colour-magnitude diagrams

We present CCD photometry for stars in three fields centered on the old open cluster NGC 188 and in four fields on the intermediate-age cluster NGC 7789, which has been performed with the aim of investigating the HR diagram distribution of the cluster's Main-Sequence (MS) stars. A sufficiently well-defined sequence of subgiant, turn-off (TO), and MS stars have been detected, extending the observed lower MS down to aboutV=20 mag.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.     

CCD photometry of BM Orionis and other trapezium stars

New light curves have been obtained for the eclipsing binary BM Orionis in theuvbyRI filter regions. The observations were made from 1988 to 1990 using the CCD photometer of the Behlen Observatory of the University of Nebraska. Reduction of all image data to magnitudes for BM Orionis and for each of the five other brightest stars in the ¹ Orionis group known as the Trapezium was accomplished by use of Stetson's DAOPHOT crowded-field photometry program. Differential magnitudes and light curves for BM Orionis and V1016 Orionis have been constructed using star D of the group as the primary comparison star. Possible indications of variability have also been looked for in the member stars C, E, and F with negative results for stars C and F and positive results for star E. The same CCD frames also contained the stars ² Orionis A and B. A light curve of the possibly-eclipsing spectroscopic binary ² Orionis A folded on its spectroscopic period does show some variability, but no obvious eclipses.     

Stellar populations as a function of radius in giant elliptical galaxies

Accurate surface photometry has been obtained inJ andK for 12 giant elliptical galaxies. Ellipses have been fitted, to obtain luminosity, ellipticity, and major axis position angle profiles. The results have been combined with visual profiles from CCD observations. We find that elliptical galaxies become bluer inV - K on the average by 0.3 (mag/sq xr _e) going outward from the nucleus. Radial colour gradients inV - K correlate strongly with those inU - V andB - V. By modelling, using theoretical isochrones, it is found that the observed colour gradients can be explained by a gradient in metallicity, if in addition the proportion of hot stars rises very rapidly with decreasing metallicity.     

Distances to galaxies from the brightest stars in the Universe

Blue Supergiants (BSGs) are the brightest stars in the universe at visual light with absolute magnitudes up to M _V =−10 mag. They are ideal stellar objects for the determination of extragalactic distances, in particular, because the perennial uncertainties troubling most of the other stellar distance indicators, interstellar extinction and metallicity, do not affect them. The quantitative spectral analysis of low resolution spectra of individual BSGs provides accurate stellar parameters and chemical composition, which are then used to determine accurate reddening and extinction from photometry for each individual object. Accurate distances can be determined from stellar gravities and effective temperatures using the “Flux Weighted Gravity–Luminosity Relationship (FGLR)”.     

Deep CCD photometry of stars in the globular cluster M3

Preliminary results on new CCD photometry inV andB bands of approximately 5000 stars in four overlapping fields in the globular cluster M3 are presented. The colour-magnitude diagram shows a very well-defined sequence with a small scatter, going fainter than previously published work on this cluster. The turn-off point found atV=19.1±0.2 mag and (B-V)=0.445±0.01, is slightly redder than those obtained in previous studies.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.     

Lichtelektrische Untersuchungen von sieben Ap-Sternen - Mitgliedern von spektroskopischen Doppelsternsystemen

Preliminary results are given for seven Ap components of spectroscopic double stars in the B, V system. In all cases the amplitudes are smaller than 0.025 mag. For no system of these seven Ap stars there was found a light variation with the period of the orbit.     

The irregular galaxy Cassiopeia 1 – a new member of the Local group

A photometry in the V, R, I (Cousins) system has been performed for stars in the galaxy Cassiopeia 1. The resulting colour-agnitude (CM) diagram of Cas 1 reveals the existence of blue stars and the absence of red ones. From an analysis of the CM diagram of the galaxy it is concluded that A_v = 4.0 mag, and the distance modulus (m – M)_o = 24.5 mag, corresponding to a distance of 790 kpc. The visual magnitude of the galaxy is V = 14^m.62 (M_v = −13^m.8) and the colour index (V – R) = 0.89 mag. From the distance determination the galaxy Cassiopeia 1 is a member of the Local group.     

Photometry of young starlike objects in the dwarf galaxy NGC 2976— age and metallicity

We present BVI_c photometry of the brightest stars andcompact star clusters in NGC 2976, a dwarf galaxy in the interacting M81/M82 group. Deep CCD images of the galaxy were obtained with the 6m‐Telescope of the Special Astrophysical Observatory (Russia) at arcsec resolution. About 290 young stars and concentrated young clusters were measured. Supplementary data in the ultraviolet are taken from the literature. The extinction to the measured objects is comparatively low, E(B — V) ∼ 0.15 .. 0.20 mag. We estimate the ages of youngest resolved stars and concentrated star clusters to be ∼5 · 10⁶ years. This population is concentrated in a broad stripe facing M81. In the central disk the population is a bit older, about 8 · 10⁶ years, this may be a hint to an outward spreading star formation process. The metallicity of the disk population is estimatedas solar (z ∼ 0.02) from a fitting to Padova theoretical stellar isochrones.     

Photometric information on globular cluster stars from the Palomar Sky Survey prints

Photometric information that can be taken from the Palomar Sky Survey prints can be used to discriminate among the various evolutionary stages of stars that are members of globular clusters, as well as to obtain some idea of the HR diagram for vary faint stars. For a test case, it is shown that in a check analysis forM3 the known turn-off luminosity is given to within about 0.5 mag. The globular cluster NGC 5466 is examined and it is concluded that no turn-off occurs beforeP20 mag.     

Johnson‐Cousins magnitudes of comparison stars in the fields of ten Seyfert galaxies

We present UBVR_CI_C magnitudes of 49 comparison stars in the fields of the Seyfert galaxies Mrk 335, Mrk 79, Mrk 279, Mrk 506, 3C 382, 3C 390.3, NGC 6814, Mrk 304, Ark 564, and NGC 7469 in order to facilitate the photometric monitoring of these objects; 36 of the stars have not been calibrated before. The comparison stars are situated in 5 × 5 arcmin fields centred on the Seyfert galaxies, their V band flux ranges from 11.7 to 18.2 mag with a median value of 16.3 mag, and their B – V colour index ranges from 0.4 to 1.6 mag with a median value of 0.8 mag. The median errors of the calibrated UBVR_CI_C magnitudes are 0.08, 0.04, 0.03, 0.04, and 0.06 mag, respectively. Comparison stars were calibrated for the first time in three of the fields (Mrk 506, 3C 382, and Mrk 304). The comparison sequences in the other fields were improved in various aspects. Extra stars were calibrated in four fields (Mrk 335, Mrk 79, NGC 6814, and NGC 7469) – most of these stars are fainter and are situated closer to the Seyfert galaxies compared to the existing comparison stars. The passband coverage of the sequences in five fields (Mrk 335, Mrk 79, Mrk 279, NGC 6814, and Ark 564) was complemented with the U band. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric variability of stars belonging to the Trapezium-type systems

We report the variability of 21 stars belonging to 17 systems considered to be Trapezium-type systems by Allenet al. (1977a). In order to avoid serious problems due to possible light contamination by neighbouring stars, we have only considered systems with angular separations between components equal or greater than five seconds of arc. Among the new variables here reported there are five having V variations greater than 0 ^m .3. For six systems we have spectrograms of the individual components. Three of the six systems are probably optical configurations and only two of the variables in the remaining three systems may be physical companions.     

Absolute magnitude calibration for red clump stars

We combined the (K _s , J?K _s ) data in Laney et al. (Mon. Not. R. Astron. Soc. 419:1637, 2012) with the V apparent magnitudes and trigonometric parallaxes taken from the Hipparcos catalogue and used them to fit the $M_{K_{s}}$ absolute magnitude to a linear polynomial in terms of V?K _s colour. The mean and standard deviation of the absolute magnitude residuals, ?0.001 and 0.195 mag, respectively, estimated for 224 red clump stars in Laney et al. (2012) are (absolutely) smaller than the corresponding ones estimated by the procedure which adopts a mean $M_{K_{s}}=-1.613~\mbox{mag}$ absolute magnitude for all red clump stars, ?0.053 and 0.218 mag, respectively. The statistics estimated by applying the linear equation to the data of 282 red clump stars in Alves (Astrophys. J. 539:732, 2000) are larger, $\Delta M_{K_{s}}=0.209$ and σ=0.524 mag, which can be explained by a different absolute magnitude trend, i.e. condensation along a horizontal distribution.     

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.