15,794 research outputs found
The VIRUS-P Exploration of Nearby Galaxies (VENGA): Survey Design, Data Processing, and Spectral Analysis Methods
We present the survey design, data reduction, and spectral fitting pipeline
for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral
field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies.
Targets span a wide range in Hubble type, star formation activity, morphology,
and inclination. The VENGA data-cubes have 5.6'' FWHM spatial resolution, ~5A
FWHM spectral resolution, sample the 3600A-6800A range, and cover large areas
typically sampling galaxies out to ~0.7 R_25. These data-cubes can be used to
produce 2D maps of the star formation rate, dust extinction, electron density,
stellar population parameters, the kinematics and chemical abundances of both
stars and ionized gas, and other physical quantities derived from the fitting
of the stellar spectrum and the measurement of nebular emission lines. To
exemplify our methods and the quality of the data, we present the VENGA
data-cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA
observations of NGC 628 are described, as well as the construction of the
data-cube, our spectral fitting method, and the fitting of the stellar and
ionized gas velocity fields. We also propose a new method to measure the
inclination of nearly face-on systems based on the matching of the stellar and
gas rotation curves using asymmetric drift corrections. VENGA will measure
relevant physical parameters across different environments within these
galaxies, allowing a series of studies on star formation, structure assembly,
stellar populations, chemical evolution, galactic feedback, nuclear activity,
and the properties of the interstellar medium in massive disk galaxies.Comment: Accepted for publication in AJ, 25 pages, 18 figures, 6 table
Galactic Rotation and Solar Motion from Stellar Kinematics
I present three methods to determine the distance to the Galactic centre R0,
the solar azimuthal velocity in the Galactic rest frame Vg,\odot and hence the
local circular speed Vc at R0. These simple, model-independent strategies
reduce the set of assumptions to near axisymmetry of the disc and are designed
for kinematically hot stars, which are less affected by spiral arms and other
effects. The first two methods use the position-dependent rotational streaming
in the heliocentric radial velocities U. The resulting rotation estimate
{\theta} from U velocities does not depend on Vg,\odot. The first approach
compares this with rotation from the galactic azimuthal velocities to constrain
Vg,\odot at an assumed R0. Both Vg,\odot and R0 can be determined using the
proper motion of Sgr A\ast as a second constraint. The second strategy makes
use of {\theta} being roughly proportional to R0. Therefore a wrong R0 can be
detected by an unphysical trend of Vg,\odot with the intrinsic rotation of
different populations. From these two strategies I estimate R0 = (8.27 \pm
0.29) kpc and Vg,\odot = (250 \pm 9) kms-1 for a stellar sample from SEGUE, or
respectively Vc = (238 \pm 9) kms-1. The result is consistent with the third
estimator, where I use the angle of the mean motion of stars, which should
follow the geometry of the Galactic disc. This method also gives the Solar
radial motion with high accuracy. The rotation effect on U velocities must not
be neglected when measuring the Solar radial velocity U\odot. It biases U\odot
in any extended sample that is lop-sided in position angle {\alpha} by of order
10 kms-1. Combining different methods I find U\odot \sim 14 kms-1, moderately
higher than previous results from the Geneva-Copenhagen Survey.Comment: Accepted by MNRAS, 15 pages, 10 figure
KOI-54: The Kepler Discovery of Tidally Excited Pulsations and Brightenings in a Highly Eccentric Binary
Kepler observations of the star HD 187091 (KIC 8112039, hereafter KOI-54) revealed a remarkable light curve exhibiting sharp periodic brightening events every 41.8 days with a superimposed set of oscillations forming a beating pattern in phase with the brightenings. Spectroscopic observations revealed that this is a binary star with a highly eccentric orbit, e = 0.83. We are able to match the Kepler light curve and radial velocities with a nearly face-on (i = 5 degrees.5) binary star model in which the brightening events are caused by tidal distortion and irradiation of nearly identical A stars during their close periastron passage. The two dominant oscillations in the light curve, responsible for the beating pattern, have frequencies that are the 91st and 90th harmonic of the orbital frequency. The power spectrum of the light curve, after removing the binary star brightening component, reveals a large number of pulsations, 30 of which have a signal-to-noise ratio greater than or similar to 7. Nearly all of these pulsations have frequencies that are either integer multiples of the orbital frequency or are tidally split multiples of the orbital frequency. This pattern of frequencies unambiguously establishes the pulsations as resonances between the dynamic tides at periastron and the free oscillation modes of one or both of the stars. KOI-54 is only the fourth star to show such a phenomenon and is by far the richest in terms of excited modes.NASA, Science Mission DirectorateNASA NNX08AR14GEuropean Research Council under the European Community 227224W.M. Keck FoundationMcDonald Observator
SOPHIE velocimetry of Kepler transit candidates XVI. Tomographic measurement of the low obliquity of KOI-12b, a warm Jupiter transiting a fast rotator
We present the detection and characterization of the transiting warm Jupiter
KOI-12b, first identified with Kepler with an orbital period of 17.86 days. We
combine the analysis of Kepler photometry with Doppler spectroscopy and
line-profile tomography of time-series spectra obtained with the SOPHIE
spectrograph to establish its planetary nature and derive its properties. To
derive reliable estimates for the uncertainties on the tomographic model
parameters, we devised an empirical method to calculate statistically
independent error bars on the time-series spectra. KOI-12b has a radius of
1.430.13 and a 3 upper mass limit of
10. It orbits a fast-rotating star (sin =
60.00.9 km s) with mass and radius of 1.450.09
and 1.630.15 , located at 42640 pc
from the Earth. Doppler tomography allowed a higher precision on the obliquity
to be reached by comparison with the analysis of the Rossiter-McLaughlin radial
velocity anomaly, and we found that KOI-12b lies on a prograde, slightly
misaligned orbit with a low sky-projected obliquity =
12.6. The properties of this planetary system,
with a 11.4 magnitude host-star, make of KOI-12b a precious target for future
atmospheric characterization.Comment: 19 pages, 10 figure
The Lyman-alpha Forest Power Spectrum from the Sloan Digital Sky Survey
We measure the power spectrum, P_F(k,z), of the transmitted flux in the
Ly-alpha forest using 3035 high redshift quasar spectra from the Sloan Digital
Sky Survey. This sample is almost two orders of magnitude larger than any
previously available data set, yielding statistical errors of ~0.6% and ~0.005
on, respectively, the overall amplitude and logarithmic slope of P_F(k,z). This
unprecedented statistical power requires a correspondingly careful analysis of
the data and of possible systematic contaminations in it. For this purpose we
reanalyze the raw spectra to make use of information not preserved by the
standard pipeline. We investigate the details of the noise in the data,
resolution of the spectrograph, sky subtraction, quasar continuum, and metal
absorption. We find that background sources such as metals contribute
significantly to the total power and have to be subtracted properly. We also
find clear evidence for SiIII correlations with the Ly-alpha forest and suggest
a simple model to account for this contribution to the power. While it is
likely that our newly developed analysis technique does not eliminate all
systematic errors in the P_F(k,z) measurement below the level of the
statistical errors, our tests indicate that any residual systematics in the
analysis are unlikely to affect the inference of cosmological parameters from
P_F(k,z). These results should provide an essential ingredient for all future
attempts to constrain modeling of structure formation, cosmological parameters,
and theories for the origin of primordial fluctuations.Comment: 92 pages, 45 of them figures, submitted to ApJ, data available at
http://feynman.princeton.edu/~pmcdonal/LyaF/sdss.htm
The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves
In the Spring of 2011 we carried out a 2.5 month reverberation mapping
campaign using the 3 m Shane telescope at Lick Observatory, monitoring 15
low-redshift Seyfert 1 galaxies. This paper describes the observations,
reductions and measurements, and data products from the spectroscopic campaign.
The reduced spectra were fitted with a multicomponent model in order to isolate
the contributions of various continuum and emission-line components. We present
light curves of broad emission lines and the AGN continuum, and measurements of
the broad H-beta line widths in mean and root-mean square (rms) spectra. For
the most highly variable AGNs we also measured broad H-beta line widths and
velocity centroids from the nightly spectra. In four AGNs exhibiting the
highest variability amplitudes, we detect anticorrelations between broad H-beta
width and luminosity, demonstrating that the broad-line region "breathes" on
short timescales of days to weeks in response to continuum variations. We also
find that broad H-beta velocity centroids can undergo substantial changes in
response to continuum variations; in NGC 4593 the broad H-beta velocity shifted
by ~250 km/s over a one-month duration. This reverberation-induced velocity
shift effect is likely to contribute a significant source of confusion noise to
binary black hole searches that use multi-epoch quasar spectroscopy to detect
binary orbital motion. We also present results from simulations that examine
biases that can occur in measurement of broad-line widths from rms spectra due
to the contributions of continuum variations and photon-counting noise.Comment: 33 pages, 28 figures, accepted for publication in ApJ Supplement
Serie
Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 from the Nuclear Stellar Dynamics
We analyze the nuclear stellar dynamics of the SB0 galaxy NGC 1023, utilizing
observational data both from the Space Telescope Imaging Spectrograph aboard
the Hubble Space Telescope and from the ground. The stellar kinematics measured
from these long-slit spectra show rapid rotation (V = 70 km/s at a distance of
0.1 arcsec = 4.9 pc from the nucleus) and increasing velocity dispersion toward
the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar
kinematics assuming an axisymmetric mass distribution with both two and three
integrals of motion. Both modeling techniques point to the presence of a
central dark compact mass (which presumably is a supermassive black hole) with
confidence > 99%. The isotropic two-integral models yield a best-fitting black
hole mass of (6.0 +/- 1.4) x 10^7 M_sun and mass-to-light ratio (M/L_V) of 5.38
+/- 0.08, and the goodness-of-fit (chi^2) is insensitive to reasonable values
for the galaxy's inclination. The three-integral models, which
non-parametrically fit the observed line-of-sight velocity distribution as a
function of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4)
x 10^7 M_sun and M/L_V of 5.56 +/- 0.02 (internal errors), and the edge-on
models are vastly superior fits over models at other inclinations. The internal
dynamics in NGC 1023 as suggested by our best-fit three-integral model shows
that the velocity distribution function at the nucleus is tangentially
anisotropic, suggesting the presence of a nuclear stellar disk. The nuclear
line of sight velocity distribution has enhanced wings at velocities >= 600
km/s from systemic, suggesting that perhaps we have detected a group of stars
very close to the central dark mass.Comment: 21 pages, 12 figures, accepted in the Astrophysical Journa
Systematic Uncertainties in Black Hole Masses Determined from Single Epoch Spectra
We explore the nature of systematic errors that can arise in measurement of
black hole masses from single-epoch spectra of active galactic nuclei (AGNs) by
utilizing the many epochs available for NGC 5548 and PG1229+204 from
reverberation mapping databases. In particular, we examine systematics due to
AGN variability, contamination due to constant spectral components (i.e.,
narrow lines and host galaxy flux), data quality (i.e., signal-to-noise ratio,
S/N), and blending of spectral features by comparing the precision and accuracy
of single-epoch mass measurements to those of recent reverberation mapping
studies. We calculate masses by characterizing the broad Hbeta emission line by
both the full width at half maximum and the line dispersion and demonstrate the
importance of removing narrow emission-line components and host starlight. We
find that the reliability of line width measurements rapidly decreases for S/N
lower than ~10 to 20 (per pixel) and that fitting the line profiles instead of
direct measurement of the data does not mitigate this problem but can, in fact,
introduce systematic errors. We also conclude that a full spectral
decomposition to deblend the AGN and galaxy spectral features is unnecessary
except to judge the contribution of the host galaxy to the luminosity and to
deblend any emission lines that may inhibit accurate line width measurements.
Finally, we present an error budget which summarizes the minimum observable
uncertainties as well as the amount of additional scatter and/or systematic
offset that can be expected from the individual sources of error investigated.
In particular, we find that the minimum observable uncertainty in single-epoch
mass estimates due to variability is ~ 20 per pixel)
spectra.Comment: 60 pages, 20 figures, accepted for publication in Ap
Broad Band Polarimetry of Supernovae: SN1994D, SN1994Y, SN1994ae, SN1995D and SN 1995H
We have made polarimetric observations of three Type Ia supernovae (SN Ia)
and two type II supernovae (SN II). No significant polarization was detected
for any of the SN Ia down to the level of 0.2\%, while polarization of order
was detected for the two SN II 1994Y and 1995H. A catalog of all the
SNe with polarization data is compiled that shows a distinct trend that all the
5 SN II with sufficient polarimetric data show polarizations at about 1\%,
while none of the 9 SN Ia in the sample show intrinsic polarization. This
systematic difference in polarization of supernovae, if confirmed, raises many
interesting questions concerning the mechanisms leading to supernova
explosions. Our observations enhance the use of SN Ia as tools for determining
the distance scale through various techniques, but suggest that one must be
very cautious in utilizing Type II for distance determinations. However, we
caution that the link between the asphericity of a supernova and the measured
``intrinsic'' polarization is complicated by reflected light from the
circumstellar material and the intervening interstellar material, the so-called
light echo. This effect may contribute more substantially to SN II than to SN
Ia. The tight limits on polarization of SN Ia may constrain progenitor models
with extensive scattering nebulae such as symbiotic stars and other systems of
extensive mass loss.Comment: 27 pages, 3 Postscript figure
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