28 research outputs found
Search for LBV Candidates in the M33 Galaxy
A total of 185 luminous blue variable (LBV) candidates with V < 18.5 and B-V
< 0.35 are selected based on the photometrical Survey of Local Group Galaxies
made by P. Massey et al. 2006. The candidates were selected using aperture
photometry of H-alpha images. The primary selection criterion is that the
prospective candidate should be a blue star with H-aplha emission. In order not
to miss appreciably reddened LBV candidates, we compose an additional list of
25 presumably reddened (0.35 < B-V < 1.2, V < 18.5) emission star candidates. A
comparison with the list of known variables in the M33 galaxy showed 29% of our
selected candidates to be photometrically variable. We also find our list to
agree well with the lists of emission-line objects obtained in earlier papers
using different methods.Comment: 6 figure
Search for Bright Massive Stars in the Galaxy IC 342
ΠΡΠ΅Π΄ΡΡΠ°Π²Π»Π΅Π½Ρ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ ΠΏΠΎΠΈΡΠΊΠ° ΡΡΠΊΠΈΡ
ΠΌΠ°ΡΡΠΈΠ²Π½ΡΡ
Π·Π²Π΅Π·Π΄ Π² Π³Π°Π»Π°ΠΊΡΠΈΠΊΠ°Ρ
Π·Π° ΠΏΡΠ΅Π΄Π΅Π»Π°ΠΌΠΈ ΠΠ΅ΡΡΠ½ΠΎΠΉ Π³ΡΡΠΏΠΏΡ Π½Π° ΠΏΡΠΈΠΌΠ΅ΡΠ΅ Π³Π°Π»Π°ΠΊΡΠΈΠΊΠΈ IC 342. ΠΡΠ»Π° ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½Π° Π·Π²Π΅Π·Π΄Π½Π°Ρ ΡΠΎΡΠΎΠΌΠ΅ΡΡΠΈΡ Π²ΠΎΡΡΠΌΠΈ ΠΏΠΎΠ»Π΅ΠΉ ΡΡΠΎΠΉ Π³Π°Π»Π°ΠΊΡΠΈΠΊΠΈ ΠΏΠΎ ΠΈΠ·ΠΎΠ±ΡΠ°ΠΆΠ΅Π½ΠΈΡΠΌ ΠΊΠΎΡΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠ΅Π»Π΅ΡΠΊΠΎΠΏΠ° Π₯Π°Π±Π±Π»Π° (HST), ΠΏΠΎΡΡΡΠΎΠ΅Π½Ρ Π‘Π-Π΄ΠΈΠ°Π³ΡΠ°ΠΌΠΌΡ. ΠΠ²Π΅Π·Π΄Π½ΡΠ΅ ΡΠΊΠΎΠΏΠ»Π΅Π½ΠΈΡ Ρ ΡΡΠΊΠΈΠΌΠΈ Π³ΠΎΠ»ΡΠ±ΡΠΌΠΈ Π·Π²Π΅Π·Π΄Π°ΠΌΠΈ, Π½Π°ΠΉΠ΄Π΅Π½Π½ΡΠ΅ ΠΏΠΎ HST-ΡΠ½ΠΈΠΌΠΊΠ°ΠΌ, ΡΡΠ°Π²Π½ΠΈΠ²Π°Π»ΠΈΡΡ Ρ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½ΠΈΠ΅ΠΌ HΞ±-ΠΎΠ±Π»Π°ΡΡΠ΅ΠΉ Π½Π° ΡΠ½ΠΈΠΌΠΊΠ°Ρ
ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΡΠ΅Π»Π΅ΡΠΊΠΎΠΏΠΎΠ². ΠΡΠΎΠ±ΡΠ°Π½ΠΎ 32 Π·Π²Π΅Π·Π΄Ρ. ΠΡΠΎΠ²Π΅Π΄Π΅Π½Ρ ΡΠΎΡΠΎΠΌΠ΅ΡΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΈ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΡΠ΅ Π½Π°Π±Π»ΡΠ΄Π΅Π½ΠΈΡ 17 ΠΎΠ±ΡΠ΅ΠΊΡΠΎΠ² Π² ΡΡΠΎΠΉ Π³Π°Π»Π°ΠΊΡΠΈΠΊΠ΅ Π½Π° 6-ΠΌΠ΅ΡΡΠΎΠ²ΠΎΠΌ ΡΠ΅Π»Π΅ΡΠΊΠΎΠΏΠ΅ ΠΠ’Π Π‘ΠΠ Π ΠΠ ΠΈ Π½Π° 3.5-ΠΌΠ΅ΡΡΠΎΠ²ΠΎΠΌ ΡΠ΅Π»Π΅ΡΠΊΠΎΠΏΠ΅ ΠΠ±ΡΠ΅ΡΠ²Π°ΡΠΎΡΠΈΠΈ ΠΠΏΠ°ΡΠΈ-ΠΠΎΠΉΠ½Ρ (Π‘Π¨Π). Π Π³Π°Π»Π°ΠΊΡΠΈΠΊΠ΅ IC 342 ΠΎΠ±Π½Π°ΡΡΠΆΠ΅Π½Ρ Π΄Π²Π° LBV-ΠΏΠΎΠ΄ΠΎΠ±Π½ΡΡ
ΠΎΠ±ΡΠ΅ΠΊΡΠ°, ΠΏΠΎΠΊΠ°Π·ΡΠ²Π°ΡΡΠΈΠ΅ ΡΠΏΠ΅ΠΊΡΡΠ°Π»ΡΠ½ΡΠ΅ ΠΈ ΡΠΎΡΠΎΠΌΠ΅ΡΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΠΈ, Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠ½ΡΠ΅ Π΄Π»Ρ ΡΠ°ΠΊΠΈΡ
Π·Π²Π΅Π·Π΄. ΠΡΠΎΠ²Π΅Π΄Π΅Π½ΠΎ ΡΡΠ°Π²Π½Π΅Π½ΠΈΠ΅ Ρ ΠΏΠΎΠ΄ΠΎΠ±Π½ΡΠΌ ΠΎΠ±ΡΠ΅ΠΊΡΠΎΠΌ Π³Π°Π»Π°ΠΊΡΠΈΠΊΠΈ Π31.The results of the search for bright massive stars in galaxies outside the Local Group are presented using the example of galaxy IC 342. Stellar photometry of eight fields of this galaxy was carried out using images from the Hubble Space Telescope (HST), CM-diagrams were constructed. Star clusters with bright blue stars found from HST images were compared with the position of HΞ± regions in the images of various telescopes. 32 stars were selected. Photometric and spectral observations of 17 objects in this galaxy were carried out on the 6-meter telescope of the BTA SAO RAS and on the 3.5-meter telescope of the Apache Point Observatory (USA). Two LBV-like objects have been found in the galaxy IC 342, showing spectral and photometric features characteristic of such stars. A comparison is made with a similar object of the galaxy M31.ΠΡ ΠΏΠΎΠ»ΡΡΠΈΠ»ΠΈ ΡΠ°ΡΡΡ Π½Π°Π±Π»ΡΠ΄Π°ΡΠ΅Π»ΡΠ½ΡΡ
Π΄Π°Π½Π½ΡΡ
Π½Π° ΡΠ½ΠΈΠΊΠ°Π»ΡΠ½ΠΎΠΉ Π½Π°ΡΡΠ½ΠΎΠΉ ΡΡΡΠ°Π½ΠΎΠ²ΠΊΠ΅ ΠΠΎΠ»ΡΡΠΎΠΉ ΡΠ΅Π»Π΅ΡΠΊΠΎΠΏ Π°Π»ΡΡ-Π°Π·ΠΈΠΌΡΡΠ°Π»ΡΠ½ΡΠΉ Π‘ΠΠ Π ΠΠ ΠΈ Π²ΡΠΏΠΎΠ»Π½ΠΈΠ»ΠΈ ΡΠ°Π±ΠΎΡΡ ΠΏΠΎ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΠ΅ ΠΈ Π°Π½Π°Π»ΠΈΠ·Ρ Π² ΡΠ°ΠΌΠΊΠ°Ρ
Π³ΡΠ°Π½ΡΠ° ΠΠΈΠ½ΠΈΡΡΠ΅ΡΡΡΠ²Π° Π½Π°ΡΠΊΠΈ ΠΈ Π²ΡΡΡΠ΅Π³ΠΎ ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΡ Π ΠΎΡΡΠΈΠΉΡΠΊΠΎΠΉ Π€Π΅Π΄Π΅ΡΠ°ΡΠΈΠΈ No 075-15-2022-262 (13.ΠΠΠΠΠ£.21.0003)
Properties of the Chandra Sources in M81
The Chandra X-ray Observatory obtained a 50-ks observation of the central
region of M81 using the ACIS-S in imaging mode. The global properties of the 97
x-ray sources detected in the inner 8.3x8.3 arcmin field of M81 are examined.
Roughly half the sources are concentrated within the central bulge. The
remainder are distributed throughout the disk with the brightest disk sources
lying preferentially along spiral arms. The average hardness ratios of both
bulge and disk sources are consistent with power law spectra of index Gamma~1.6
indicative of a population of x-ray binaries. A group of much softer sources
are also present. The background source-subtracted logN-logS distribution of
the disk follows a power law of index ~ -0.5 with no change in slope over three
decades in flux. The logN-logS distribution of the bulge follows a similar
shape but with a steeper slope above ~4.0e+37 ergs/s. There is unresolved x-ray
flux from the bulge with a radial profile similar to that of the bulge sources.
This unresolved flux is softer than the average of the bulge sources and
extrapolating the bulge logN-logS distribution towards weaker sources can only
account for 20% of the unresolved flux. No strong time variability was observed
for any source with the exception of one bright, soft source.Comment: 5 pages, 3 color PS figures, to appear in ApJ
Investigation of the New Local Group Galaxy VV 124
We present the results of our stellar photometry and spectroscopy for the new
Local Group galaxy VV 124 (UGC 4879) obtained with the 6-m BTA telescope. The
presence of a few bright supergiants in the galaxy indicates that the current
star formation process is weak. The apparent distribution of stars with
different ages in VV 124 does not differ from the analogous distributions of
stars in irregular galaxies, but the ratio of the numbers of young and old
stars indicates that VV 124 belongs to the rare Irr/Sph type of galaxies. The
old stars (red giants) form the most extended structure, a thick disk with an
exponential decrease in the star number density to the edge. Definitely, the
young population unresolvable in images makes a great contribution to the
background emission from the central galactic regions. The presence of young
stars is also confirmed by the [O III] emission line visible in the spectra
that belongs to extensive diffuse galactic regions. The mean radial velocity of
several components (two bright supergiants, the unresolvable stellar
population, and the diffuse gas) is v_h = -70+/-15 km/s and the velocity with
which VV 124 falls into the Local Group is v_LG = -12+/-15 km/s. We confirm the
distance to the galaxy D = 1.1+/-0.1 Mpc and the metallicity of red giants
([Fe/H] = -1.37) found by Kopylov et al. (2008).VV 124 is located on the
periphery of the Local Group approximately at the same distance from M 31 and
our Galaxy and is isolated from other galaxies. The galaxy LeoA nearest to it
is 0.5 Mpc away.Comment: 10 pages, 8 figures. Accepted for publication in Astronomy Letters
(2010, Vol. 36, No. 5, pp. 309-318
Instability of LBV-stars against radial oscillations
In this study we consider the nonlinear radial oscillations exciting in
LBV--stars with effective temperatures 1.5e4 K <= Teff <= 3e4 K, bolometric
luminosities 1.2e6 L_odot <= L <= 1.9e6 L_odot and masses 35.7 M_odot <= M <=
49.1 M_odot. Hydrodynamic computations were carried out with initial conditions
obtained from evolutionary sequences of population I stars (X=0.7, Z=0.02) with
initial masses from 70M_odot to 90 M_odot. All hydrodynamical models show
instability against radial oscillations with amplitude growth time comparable
with dynamical time scale of the star. Radial oscillations exist in the form of
nonlinear running waves propagating from the boundary of the compact core to
the upper boundary of the hydrodynamical model. The velocity amplitude of outer
layers is of several hundreds of km/s while the bolometric light amplitude does
not exceed 0.2 mag. Stellar oscillations are not driven by the kappa-mechanism
and are due to the instability of the gas with adiabatic exponent close to the
critical value Gamma_1 = 4/3 due to the large contribution of radiation in the
total pressure. The range of the light variation periods (6 day <= P <= 31 day)
of hydrodynamical models agrees with periods of microvariability observed in
LBV--stars.Comment: 14 pages, 5 figures, submitted to Astronomy Letter
MN112: a new Galactic candidate Luminous Blue Variable
We report the discovery of a new Galactic candidate Luminous Blue Variable
(cLBV) via detection of an infrared circular nebula and follow-up spectroscopy
of its central star. The nebula, MN112, is one of many dozens of circular
nebulae detected at m in the {\it Spitzer Space Telescope} archival
data, whose morphology is similar to that of nebulae associated with known
(c)LBVs and related evolved massive stars. Specifically, the core-halo
morphology of MN112 bears a striking resemblance to the circumstellar nebula
associated with the Galactic cLBV GAL 079.29+00.46, which suggests that both
nebulae might have a similar origin and that the central star of MN112 is a
LBV. The spectroscopy of the central star showed that its spectrum is almost
identical to that of the bona fide LBV P Cygni, which also supports the LBV
classification of the object. To further constrain the nature of MN112, we
searched for signatures of possible high-amplitude (\ga 1 mag) photometric
variability of the central star using archival and newly obtained photometric
data covering a 45 year period. We found that the B magnitude of the star was
constant ( 17.10.3 mag) over this period, while in the I band the
star brightened by mag during the last 17 years. Although the
non-detection of large photometric variability leads us to use the prefix
`candidate' in the classification of MN112, we remind that the long-term
photometric stability is not unusual for genuine LBVs and that the brightness
of P Cygni remains relatively stable during the last three centuries.Comment: 6 pages, 3 figures, accepted to MNRA
Two New LBV Candidates in the M33 Galaxy
We present two new luminous blue variable (LBV) candidate stars discovered in
the M33 galaxy. We identified these stars (Valeev et al. 2010) as massive star
candidates at the final stages of evolution, presumably with a notable
interstellar extinction. The candidates were selected from the Massey et al.
(2006) catalog based on the following criteria: emission in Halpha, V<18.5 and
0.35<(B-V)<1.2. The spectra of both stars reveal a broad and strong Halpha
emission with extended wings (770 and 1000 km/s). Based on the spectra we
estimated the main parameters of the stars. Object N45901 has a bolometric
luminosity log(L/Lsun)=6.0-6.2 with the value of interstellar extinction
Av=2.3+-0.1. The temperature of the star's photosphere is estimated as
Tstar~13000-15000K its probable mass on the Zero Age Main Sequence is
M~60-80Msun. The infrared excess in N45901 corresponds to the emission of warm
dust with the temperature Twarm~1000K, and amounts to 0.1% of the bolometric
luminosity. A comparison of stellar magnitude estimates from different catalogs
points to the probable variability of the object N45901. Bolometric luminosity
of the second object, N125093, is log(L/Lsun)=6.3-6.6, the value of
interstellar extinction is Av=2.75+-0.15. We estimate its photosphere's
temperature as Tstar~13000-16000K, the initial mass as M~90-120Msun. The
infrared excess in N125093 amounts to 5-6% of the bolometric luminosity. Its
spectral energy distribution reveals two thermal components with the
temperatures Twarm~1000K and Tcold~480K. The [CaII] lines (7291A and 7323A),
observed in LBV-like stars VarA and N93351 in M33, are also present in the
spectrum of N125093. These lines indicate relatively recent gas eruptions and
dust activity linked with them. High bolometric luminosity of these stars and
broad Halpha emissions allow classifying the studied objects as LBV candidates.Comment: 14 pages, 4 figure
Optical Identification of Four Hard X-ray Sources from the Swift All-Sky Survey
We present the results of our optical identifications of four hard X-ray
sources from the Swift all-sky survey. We obtained optical spectra for each of
the program objects with the 6-m BTA telescope (Special Astrophysical
Observatory, Russian Academy of Sciences, Nizhnii Arkhyz), which allowed their
nature to be established. Two sources (SWIFT J2237.2+6324} and SWIFT
J2341.0+7645) are shown to belong to the class of cataclysmic variables
(suspected polars or intermediate polars). The measured emission line width
turns out to be fairly large (FWHM ~ 15-25 A), suggesting the presence of
extended, rapidly rotating (v~400-600 km/s) accretion disks in the systems.
Apart from line broadening, we have detected a change in the positions of the
line centroids for SWIFT J2341.0+7645, which is most likely attributable to the
orbital motion of the white dwarf in the binary system. The other two program
objects (SWIFT J0003.3+2737 and SWIFT J0113.8+2515) are extragalactic in
origin: the first is a Seyfert 2 galaxy and the second is a blazar at redshift
z=1.594. Apart from the optical spectra, we provide the X-ray spectra for all
sources in the 0.6-10 keV energy band obtained from XRT/Swift data.Comment: 9 pages, 6 figures, will be published in Astronomy Letters, 38, No.5,
pp.281-289 (2012