17 research outputs found
SDSS surface photometry of M 31 with absorption corrections
The objective of this work is to obtain an extinction-corrected distribution
of optical surface brightness and colour indices of the large nearby galaxy M
31 using homogeneous observational data and a model for intrinsic extinction.
We process the Sloan Digital Sky Survey (SDSS) images in ugriz passbands and
construct corresponding mosaic images, taking special care of subtracting the
varying sky background. We apply the galactic model developed in Tempel et al.
(2010) and far-infrared imaging to correct the photometry for intrinsic dust
effects.
We obtain observed and dust-corrected distributions of the surface brightness
of M 31 and a map of line-of-sight extinctions inside the galaxy. Our
extinction model suggests that either M 31 is intrinsically non-symmetric along
the minor axis or the dust properties differ from those of the Milky Way.
Assuming the latter case, we present the surface brightness distributions and
integral photometry for the Sloan filters as well as the standard UBVRI system.
We find the following intrinsic integral colour indices for M 31: (U-B)_0=0.35;
(B-V)_0=0.86; (V-R)_0=0.63; (R-I)_0=0.53; the total intrinsic
absorption-corrected luminosities of M 31 in the B and the V filters are 4.10
and 3.24 mag, respectively.Comment: 6 pages, 8 figures, accepted for publication in A&A. The
high-resolution zoomable colour image of M 31 can be seen at
http://www.aai.ee/~elmo/m31
Variability survey of brightest stars in selected OB associations
The stellar evolution theory of massive stars remains uncalibrated with
high-precision photometric observational data mainly due to a small number of
luminous stars that are monitored from space. Automated all-sky surveys have
revealed numerous variable stars but most of the luminous stars are often
overexposed. Targeted campaigns can improve the time base of photometric data
for those objects.
The aim of this investigation is to study the variability of luminous stars
at different timescales in young open clusters and OB associations.
We monitored 22 open clusters and associations from 2011 to 2013 using a
0.25-m telescope. Variable stars were detected by comparing the overall
light-curve scatter with measurement uncertainties. Variability was analysed by
the light curve feature extraction tool FATS. Periods of pulsating stars were
determined using the discrete Fourier transform code SigSpec. We then
classified the variable stars based on their pulsation periods and available
spectral information.
We obtained light curves for more than 20000 sources of which 354 were found
to be variable. Amongst them we find 80 eclipsing binaries, 31 Cyg, 13
Cep, 62 Be, 16 slowly pulsating B, 7 Cepheid, 1 Doradus, 3
Wolf-Rayet and 63 late-type variable stars. Up to 55% of these stars are
potential new discoveries as they are not present in the Variable Star Index
(VSX) database. We find the cluster membership fraction for variable stars to
be 13% with an upper limit of 35%.Comment: 36 pages, 11 figures, catalogue in appendix
Period change of massive binaries from combined photometric and spectroscopic data in Cygnus OB2
Context. Mass loss is an important property in evolution models of massive
stars. As up to 90% of the massive stars have a visual or spectroscopic
companion and many of them exhibit mass exchange, mass-loss rates can be
acquired through the period study of massive binaries.
Aims. Using our own photometric observations as well as archival data, we
look for variations in orbital periods of seven massive eclipsing binary
systems in the Cygnus OB2 association and estimate their mass-loss rates and
stellar parameters.
Methods. We use a Bayesian parameter estimation method to simultaneously fit
the period and period change to all available data and a stellar modelling tool
to model the binary parameters from photometric and radial-velocity data.
Results. Four out of the seven selected binaries show non-zero period change
values at two-sigma confidence level. We also report for the first time the
eclipsing nature of a star MT059.Comment: 12 pages, 18 figures, accepted for publication in A&
Spiral arms and disc stability in the Andromeda galaxy
Aims: Density waves are often considered as the triggering mechanism of star
formation in spiral galaxies. Our aim is to study relations between different
star formation tracers (stellar UV and near-IR radiation and emission from HI,
CO and cold dust) in the spiral arms of M31, to calculate stability conditions
in the galaxy disc and to draw conclusions about possible star formation
triggering mechanisms.
Methods: We select fourteen spiral arm segments from the de-projected data
maps and compare emission distributions along the cross sections of the
segments in different datasets to each other, in order to detect spatial
offsets between young stellar populations and the star forming medium. By using
the disc stability condition as a function of perturbation wavelength and
distance from the galaxy centre we calculate the effective disc stability
parameters and the least stable wavelengths at different distances. For this we
utilise a mass distribution model of M31 with four disc components (old and
young stellar discs, cold and warm gaseous discs) embedded within the external
potential of the bulge, the stellar halo and the dark matter halo. Each
component is considered to have a realistic finite thickness.
Results: No systematic offsets between the observed UV and CO/far-IR emission
across the spiral segments are detected. The calculated effective stability
parameter has a minimal value Q_{eff} ~ 1.8 at galactocentric distances 12 - 13
kpc. The least stable wavelengths are rather long, with the minimal values
starting from ~ 3 kpc at distances R > 11 kpc.
Conclusions: The classical density wave theory is not a realistic explanation
for the spiral structure of M31. Instead, external causes should be considered,
e.g. interactions with massive gas clouds or dwarf companions of M31.Comment: 12 pages, 8 figures, Astron & Astrophys accepte
Quantifying torque from the Milky Way bar using Gaia DR2
We determine the mass of the Milky Way bar and the torque it causes, using
Gaia DR2, by applying the orbital arc method. Based on this, we have found that
the gravitational acceleration is not directed towards the centre of our Galaxy
but a few degrees away from it. We propose that the tangential acceleration
component is caused by the bar of the Galaxy. Calculations based on our model
suggest that the torque experienced by the region around the Sun is per solar mass. The mass estimate for the bar is . Using greatly improved data from Gaia DR2, we
have computed the acceleration field to great accuracy by adapting the oPDF
method (Han et al. 2016) locally and used the phase space coordinates of stars within a distance of 0.5 kpc from the Sun. In the orbital
arc method, the first step is to guess an acceleration field and then
reconstruct the stellar orbits using this acceleration for all the stars within
a specified region. Next, the stars are redistributed along orbits to check if
the overall phase space distribution has changed. We repeat this process until
we find an acceleration field that results in a new phase space distribution
that is the same as the one that we started with; we have then recovered the
true underlying acceleration.Comment: 12 pages, 6 figures, accepted to MNRA
Multiscale cosmic web detachments, connectivity, and preprocessing in the supercluster SClA2142 cocoon
We study the properties, connectivity, and galaxy content of groups and
filaments in the low-density region (cocoon) around A2142 supercluster
(SClA2142). We traced the SClA2142 cocoon boundaries by the lowest
luminosity-density regions that separate SClA2142 from other superclusters. We
determined galaxy filaments and groups in the cocoon and analysed the
connectivity of groups, the high density core (HDC) of the supercluster, and
the whole of the supercluster. We compared the distribution and properties of
galaxies with different star-formation properties in the supercluster and in
the cocoon. SClA2142 and the long filament that is connected to it forms the
longest straight structure in the Universe detected so far, with a length of
Mpc. The connectivity of the supercluster is C = 6 - 7; poor
groups have C = 1 - 2. Long filaments around the supercluster's main body are
detached from it at the turnaround region. Galaxies with very old stellar
populations lie in systems across a wide range of richness from the richest
cluster to poorest groups and single galaxies. They lie even at local densities
as low as in the supercluster.
Recently quenched galaxies lie in the cocoon mainly in one region and their
properties are different in the cocoon and in the supercluster. The
star-formation properties of single galaxies are similar across all
environments. The collapsing main body of SClA2142 with the detached long
filaments near it are evidence of an important epoch in the supercluster
evolution. Further studies are needed to understand the reasons of similarity
of galaxies with very old stellar populations in extremely different
environments. The presence of long, straight structures in the cosmic web may
serve as a test for cosmological models.Comment: 20 pages, 14 figures, accepted for publication in A&
Multiscale cosmic web detachments, connectivity, and preprocessing in the supercluster SCl A2142 cocoon
Context. Superclusters of galaxies and their surrounding low-density regions (cocoons) represent dynamically evolving environments in which galaxies and their systems form and evolve. While evolutionary processes of galaxies in dense environments are extensively studied at present, galaxy evolution in low-density regions has received less attention.Aims. We study the properties, connectivity, and galaxy content of groups and filaments in the A2142 supercluster (SCl A2142) cocoon to understand the evolution of the supercluster with its surrounding structures and the galaxies within them.Methods. We calculated the luminosity-density field of SDSS galaxies and traced the SCl A2142 cocoon boundaries by the lowest luminosity-density regions that separate SCl A2142 from other superclusters. We determined galaxy filaments and groups in the cocoon and analysed the connectivity of groups, the high density core (HDC) of the supercluster, and the whole of the supercluster. We compared the distribution and properties of galaxies with different star-formation properties in the supercluster and in the cocoon.Results. The supercluster A2142 and the long filament that is connected to it forms the longest straight structure in the Universe detected so far, with a length of approximately 75 h(-1) Mpc. The connectivity of the cluster A2142 and the whole supercluster is C=6-7; poor groups exhibit C=1-2. Long filaments around the supercluster's main body are detached from it at the turnaround region. Among various local and global environmental trends with regard to the properties of galaxies and groups, we find that galaxies with very old stellar populations lie in systems across a wide range of richness from the richest cluster to poorest groups and single galaxies. They lie even at local densities as low as D1 800 in the supercluster. Recently quenched galaxies lie in the cocoon mainly in one region and their properties are different in the cocoon and in the supercluster. The star-formation properties of single galaxies are similar across all environments.Conclusions. The collapsing main body of SCl A2142 with the detached long filaments near it are evidence of an important epoch in the supercluster evolution. There is a need for further studies to explore possible reasons behind the similarities between galaxies with very old stellar populations in extremely different environments, as well as mechanisms for galaxy quenching at very low densities. The presence of long, straight structures in the cosmic web may serve as a test for cosmological models
Quantifying torque from the Milky Way bar using Gaia DR2
We determine the mass of the Milky Way bar and the torque it causes, using Gaia DR2, by applying the orbital arc method. Based on this, we have found that the gravitational acceleration is not directed towards the centre of our Galaxy but a few degrees away from it. We propose that the tangential acceleration component is caused by the bar of the Galaxy. Calculations based on our model suggest that the torque experienced by the region around the Sun is per solar mass. The mass estimate for the bar is . Using greatly improved data from Gaia DR2, we have computed the acceleration field to great accuracy by adapting the orbital Probability Density Function (oPDF) method (Han et al. 2016) locally and used the phase space coordinates of ∼4 × 105 stars within a distance of 0.5 kpc from the Sun. In the orbital arc method, the first step is to guess an acceleration field and then reconstruct the stellar orbits using this acceleration for all the stars within a specified region. Next, the stars are redistributed along orbits to check if the overall phase space distribution has changed. We repeat this process until we find an acceleration field that results in a new phase space distribution that is the same as the one that we started with; we have then recovered the true underlying acceleration