122 research outputs found
Discovery of Variability of the Progenitor of SN 2011dh in M51 Using the Large Binocular Telescope
We show that the candidate progenitor of the core-collapse SN 2011dh in M51
(8 Mpc away) was fading by 0.039 +- 0.006 mag/year during the three years prior
to the supernova, and that this level of variability is moderately unusual for
other similar stars in M 51. While there are uncertainties about whether the
true progenitor was a blue companion to this candidate, the result illustrates
that there are no technical challenges to obtaining fairly high precision light
curves of supernova progenitors using ground based observations of nearby (<10
Mpc) galaxies with wide field cameras on 8m-class telescopes. While other
sources of variability may dominate, it is even possible to reach into the
range of evolution rates required by the quasi-static evolution of the stellar
envelope. For M 81, where we have many more epochs and a slightly longer time
baseline, our formal 3 sigma sensitivity to slow changes is presently 3
millimag/year for a M_V ~= -8 mag star. In short, there is no observational
barrier to determining whether the variability properties of stars in their
last phases of evolution (post Carbon ignition) are different from earlier
phases.Comment: 17 pages, 5 figures, submitted to Ap
Body weight and the medial longitudinal foot arch : high-arched foot, a hidden problem?
This study had two objectives. First, to determine the prevalence of hollow (high-arched) and flat foot among primary school children in Cracow (Poland). Second, to evaluate the relationship between the type of medial longitudinal arch (MLA; determined by the Clarke’s angle) and degree of fatness. The prevalence of underweight, overweight, and obesity was determined by means of IOTF cut-offs with respect to age and gender. A sample of 1,115 children (564 boys and 551 girls) aged between 3 and 13 years was analyzed. In all age groups, regardless of gender, high-arched foot was diagnosed in the majority of children. A distinct increase in the number of children with high-arched foot was observed between 7- and 8-year olds. Regardless of the gender, high-arched foot was more common among underweight children. In the group of obese children, the biggest differences were attributed to gender. High-arched foot was the most frequently observed among boys. In all gender and obesity level groups, the flat foot was more common among boys than among girls. Conclusions: High-arched foot is the most common foot defect among children 3–13 years old regardless of gender. Flat foot is least frequently observed in children 3–13 years old. A statistic correlation between MLA and adiposity is observed. Stronger correlation is observed among girls
On Absorption by Circumstellar Dust, With the Progenitor of SN2012aw as a Case Study
We use the progenitor of SN2012aw to illustrate the consequences of modeling
circumstellar dust using Galactic (interstellar) extinction laws that (1)
ignore dust emission in the near-IR and beyond; (2) average over dust
compositions, and (3) mis-characterize the optical/UV absorption by assuming
that scattered photons are lost to the observer. The primary consequences for
the progenitor of SN2012aw are that both the luminosity and the absorption are
significantly over-estimated. In particular, the stellar luminosity is most
likely in the range 10^4.8 < L/Lsun < 10^5.0 and the star was not extremely
massive for a Type IIP progenitor, with M < 15Msun. Given the properties of the
circumstellar dust and the early X-ray/radio detections of SN2012aw, the star
was probably obscured by an on-going wind with Mdot ~ 10^-5.5 to 10^-5.0
Msun/year at the time of the explosion, roughly consistent with the expected
mass loss rates for a star of its temperature (T_* ~ 3600K) and luminosity. In
the spirit of Galactic extinction laws, we supply simple interpolation formulas
for circumstellar extinction by dusty graphitic and silicate shells as a
function of wavelength (>0.3 micron) and total (absorption plus scattering)
V-band optical depth (tau < 20). These do not include the contributions of dust
emission, but provide a simple, physical alternative to incorrectly using
interstellar extinction laws.Comment: Submitted to Ap
The Absolute Magnitude of RRc Variables From Statistical Parallax
We present the first definitive measurement of the absolute magnitude of RR
Lyrae c-type variable stars (RRc) determined purely from statistical parallax.
We use a sample of 247 RRc selected from the All Sky Automated Survey (ASAS)
for which high-quality light curves, photometry and proper motions are
available. We obtain high-resolution echelle spectra for these objects to
determine radial velocities and abundances as part of the Carnegie RR Lyrae
Survey (CARRS). We find that M_(V,RRc) = 0.52 +/- 0.11 at a mean metallicity of
[Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars
(M_(V,RRab) = 0.75 +/- 0.13 and the only direct measurement of an RRc absolute
magnitude (RZ Cephei, M_(V, RRc) = 0.27 +/- 0.17). We find the bulk velocity of
the halo to be (W_pi, W_theta, W_z) = (10.9,34.9,7.2) km/s in the radial,
rotational and vertical directions with dispersions (sigma_(W_pi),
sigma_(W_theta), sigma_(W_z)) = (154.7, 103.6, 93.8) km/s. For the disk, we
find (W_pi, W_theta, W_z) = (8.5, 213.2, -22.1) km/s with dispersions
(sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (63.5, 49.6, 51.3) km/s.
Finally, we suggest that UCAC2 proper motion errors may be overestimated by
about 25%Comment: Submitted to ApJ. 11 pages including 6 figure
The Mid-IR Contribution Of Dust Enshrouded Stars In Six Nearby Galaxies
We measure the integrated contributions of dusty AGB stars and other luminous
red mid-IR sources to the mid-IR luminosities of 6 galaxies (M81, NGC 2403, NGC
300, M33 and the Magellanic Clouds). We find the dusty AGB stars whose mid-IR
fluxes are dominated by dust rather than photospheric emission contribute from
0.6% (M81) to 5.6% (SMC) of the 3.6 micron flux and 1.0% (M81) to 10.1% (SMC)
of the 4.5 micron flux. We find a trend of decreasing AGB contribution with
increasing galaxy metallicity, luminosity and mass and decreasing SSFR.
However, these galaxy properties are strongly correlated in our sample and the
simplest explanation of the trend is galaxy metallicity. Bright, red sources
other than dusty AGB stars represent a smaller fraction of the luminosity,
~1.2% at 3.6 microns, however their dust is likely cooler and their
contributions are likely larger at longer wavelengths. Excluding the SMC, the
contribution from these red sources correlates with the specific star formation
rate as we would expect for massive stars. In total, after correcting for dust
emission at other wavelengths, the dust around AGB stars radiates 0.1-0.8% of
the bolometric luminosities of the galaxies. Thus, hot dust emission from AGB
and other luminous dusty stars represent a small fraction of the total
luminosities of the galaxies but a significant fraction of their mid-IR
emissions.Comment: 9 pages, 6 figures, published in ApJ. For a brief video explaining
the key results of this paper, see http://www.youtube.com/user/OSUAstronom
RR Lyrae variables in M32 and the disk of M31
We observed two fields near M32 with the Advanced Camera for Surveys/High
Resolution Channel (ACS/HRC) on board the Hubble Space Telescope (HST). The
main field, F1, is 1.8 arcmin from the center of M32; the second field, F2,
constrains the M31 background, and is 5.4 arcmin distant. Each field was
observed for 16-orbits in each of the F435W (narrow B) and F555W (narrow V)
filters. The duration of the observations allowed RR Lyrae stars and other
short-period variables to be detected. A population of RR Lyrae stars
determined to belong to M32 would prove the existence of an ancient population
in that galaxy, a subject of some debate. We detected 17 RR Lyrae variables in
F1 and 14 in F2. A 1-sigma upper limit of 6 RR Lyrae variables belonging to M32
is inferred from these two fields alone. Use of our two ACS/WFC parallel fields
provides better constraints on the M31 background, however, and implies that
(68 % confidence interval) RR Lyrae variables in F1 belong to
M32. We have therefore found evidence for an ancient population in M32. It
seems to be nearly indistinguishable from the ancient population of M31. The RR
Lyrae stars in the F1 and F2 fields have indistinguishable mean V-band
magnitudes, mean periods, distributions in the Bailey diagram and ratios of RRc
to RR(tot) types. However, the color distributions in the two fields are
different, with a population of red RRab variables in F1 not seen in F2. We
suggest that these might be identified with the detected M32 RR Lyrae
population, but the small number of stars rules out a definitive claim.Comment: 19 pages, 18 figures, accepted Ap
SN 2010jl in UGC 5189: Yet another luminous type IIn supernova in a metal-poor galaxy
We present ASAS data starting 25 days before the discovery of the recent type
IIn SN 2010jl, and we compare its light curve to other luminous IIn SNe,
showing that it is a luminous (M_I ~ -20.5) event. Its host galaxy, UGC 5189,
has a low gas-phase oxygen abundance (12 + log(O/H) = 8.2), which reinforces
the emerging trend that over-luminous core-collapse supernovae are found in the
low-metallicity tail of the galaxy distribution, similar to the known trend for
the hosts of long GRBs. We compile oxygen abundances from the literature and
from our own observations of UGC 5189, and we present an unpublished spectrum
of the luminous type Ic SN 2010gx that we use to estimate its host metallicity.
We discuss these in the context of host metallicity trends for different
classes of core-collapse objects. The earliest generations of stars are known
to be enhanced in [O/Fe] relative to the Solar mixture; it is therefore likely
that the stellar progenitors of these overluminous supernovae are even more
iron-poor than they are oxygen-poor. A number of mechanisms and massive star
progenitor systems have been proposed to explain the most luminous
core-collapse supernovae; any successful theory will need to include the
emerging trend that points towards low-metallicity for the massive progenitor
stars. This trend for very luminous supernovae to strongly prefer
low-metallicity galaxies should be taken into account when considering various
aspects of the evolution of the metal-poor early universe. (abridged)Comment: 27 pages, 7 figures, 2 tables. Accepted for publication in Ap
Crossing the Gould Belt in the Orion vicinity
We present a study of the large-scale spatial distribution of 6482 RASS X-ray
sources in approximately 5000 deg^2 in the direction of Orion. We examine the
astrophysical properties of a sub-sample of ~100 optical counterparts, using
optical spectroscopy. This sub-sample is used to investigate the space density
of the RASS young star candidates by comparing X-ray number counts with
Galactic model predictions. We characterize the observed sub-sample in terms of
spectral type, lithium content, radial and rotational velocities, as well as
iron abundance. A population synthesis model is then applied to analyze the
stellar content of the RASS in the studied area. We find that stars associated
with the Orion star-forming region do show a high lithium content. A population
of late-type stars with lithium equivalent widths larger than Pleiades stars of
the same spectral type (hence younger than ~70-100 Myr) is found widely spread
over the studied area. Two new young stellar aggregates, namely "X-ray Clump
0534+22" (age~2-10 Myr) and "X-ray Clump 0430-08" (age~2-20 Myr), are also
identified. The spectroscopic follow-up and comparison with Galactic model
predictions reveal that the X-ray selected stellar population in the direction
of Orion is characterized by three distinct components, namely the clustered,
the young dispersed, and the widespread field populations. The clustered
population is mainly associated with regions of recent or ongoing star
formation and correlates spatially with molecular clouds. The dispersed young
population follows a broad lane apparently coinciding spatially with the Gould
Belt, while the widespread population consists primarily of active field stars
older than 100 Myr. We expect the "bi-dimensional" picture emerging from this
study to grow in depth as soon as the distance and the kinematics of the
studied sources will become available from the future Gaia mission.Comment: 17 pages, 13 figures, 4 tables. Accepted for publication in Astronomy
and Astrophysics. Abstract shortene
A model of AW UMa
The contact binary AW UMa has an extreme mass ratio, with the more massive
component (the current primary) close to the main sequence, while the low mass
star at q ~ 0.1 (the current secondary) has a much larger radius than a main
sequence star of a comparable mass. We propose that the current secondary has
almost exhausted hydrogen in its center and is much more advanced in its
evolution, as suggested by Stepien. Presumably the current secondary lost most
of its mass during its evolution with part of it transferred to the current
primary. After losing a large fraction of its angular momentum, the binary may
evolve into a system of FK Com type.Comment: 5 pages, 6 figures, Accepted to MNRAS, content change
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