17 research outputs found
Testing the Disk Regulation Paradigm with Spitzer Observations. II. A Clear Signature of Star-Disk Interaction in NGC 2264 and the Orion Nebula Cluster
Observations of PMS star rotation periods reveal slow rotators in young
clusters of various ages, indicating that angular momentum is somehow removed
from these rotating masses. The mechanism by which spin-up is regulated as
young stars contract has been one of the longest-standing problems in star
formation. Attempts to observationally confirm the prevailing theory that
magnetic interaction between the star and its circumstellar disk regulates
these rotation periods have produced mixed results. In this paper, we use the
unprecedented disk identification capability of the Spitzer Space Telescope to
test the star-disk interaction paradigm in two young clusters, NGC 2264 and the
Orion Nebula Cluster (ONC). We show that once mass effects and sensitivity
biases are removed, a clear increase in the disk fraction with period can be
observed in both clusters across the entire period range populated by cluster
members. We also show that the long-period peak (P 8 days) of the bimodal
distribution observed for high-mass stars in the ONC is dominated by a
population of stars possessing a disk, while the short-period peak (P 2
days) is dominated by a population of stars without a disk. Our results
represent the strongest evidence to date that star-disk interaction regulates
the angular momentum of these young stars. This study will make possible
quantitative comparisons between the observed period distributions of stars
with and without a disk and numerical models of the angular momentum evolution
of young stars.Comment: 31 pages, 7 figures, 2 tables. Accepted for publication in Ap
TrES-3: A Nearby, Massive, Transiting Hot Jupiter in a 31-Hour Orbit
We describe the discovery of a massive transiting hot Jupiter with a very
short orbital period (1.30619 d), which we name TrES-3. From spectroscopy of
the host star GSC 03089-00929, we measure T_eff = 5720 +- 150 K, logg=4.6 +-
0.3, and vsini < 2 km/s, and derive a stellar mass of 0.90 +- 0.15 M_sun. We
estimate a planetary mass of 1.92 +- 0.23 M_Jup, based on the sinusoidal
variation of our high-precision radial velocity measurements. This variation
has a period and phase consistent with our transit photometry. Our spectra show
no evidence of line bisector variations that would indicate a blended eclipsing
binary star. From detailed modeling of our B and z photometry of the 2.5%-deep
transits, we determine a stellar radius 0.802 +- 0.046 R_sun and a planetary
radius 1.295 +- 0.081 R_Jup. TrES-3 has one of the shortest orbital periods of
the known transiting exoplanets, facilitating studies of orbital decay and mass
loss due to evaporation, and making it an excellent target for future studies
of infrared emission and reflected starlight.Comment: v1. 14 pages, 2 figures, 3 tables. Submitted to ApJL 27 April 2007.
Accepted for publication in ApJL 14 May 200
A New Spectroscopic and Photometric Analysis of the Transiting Planet Systems TrES-3 and TrES-4
We report new spectroscopic and photometric observations of the parent stars of the recently discovered transiting planets TrES-3 and TrES-4. A detailed abundance analysis based on high-resolution spectra yields [Fe/H] = â0.19 ± 0.08, T_(eff) = 5650 ± 75 K, and log g = 4.4 ± 0.1 for TrES-3, and [Fe/H] = +0.14 ± 0.09, T_(eff) = 6200 ± 75 K, and log g = 4.0 ± 0.1 for TrES-4. The accuracy of the effective temperatures is supported by a number of independent consistency checks. The spectroscopic orbital solution for TrES-3 is improved with our new radial velocity measurements of that system, as are the light-curve parameters for both systems based on newly acquired photometry for TrES-3 and a reanalysis of existing photometry for TrES-4. We have redetermined the stellar parameters taking advantage of the strong constraint provided by the light curves in the form of the normalized separation a/R_* (related to the stellar density) in conjunction with our new temperatures and metallicities. The masses and radii we derive are M_* = 0.928^(+0.028)_(â0.048) M_â, R_* = 0.829^(+0.015)_(â0.022) R_â, and M_* = 1.404^(+0.066)_(â0.134) M_â, R_* = 1.846^(+0.096)_(â0.087) R_â for TrES-3 and TrES-4, respectively. With these revised stellar parameters, we obtain improved values for the planetary masses and radii. We find M_p = 1.910^(+0.075)_(â0.080) M_(Jup), R_p = 1.336^(+0.031)_(â0.036) R_(Jup) for TrES-3, and M_p = 0.925 ± 0.082 M_(Jup), R_p = 1.783^(+0.093)_(â0.086) R_(Jup) for TrES-4. We confirm TrES-4 as the planet with the largest radius among the currently known transiting hot Jupiters
The Lick AGN Monitoring Project: Reverberation Mapping of Optical Hydrogen and Helium Recombination Lines
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission, which we have previously reported. We present here the light
curves for the Halpha, Hgamma, HeII 4686, and HeI 5876 emission lines and the
time lags for the emission-line responses relative to changes in the continuum
flux. Combining each emission-line time lag with the measured width of the line
in the variable part of the spectrum, we determine a virial mass of the central
supermassive black hole from several independent emission lines. We find that
the masses are generally consistent within the uncertainties. The time-lag
response as a function of velocity across the Balmer line profiles is examined
for six of the AGNs. Finally we compare several trends seen in the dataset
against the predictions from photoionization calculations as presented by
Korista & Goad. We confirm several of their predictions, including an increase
in responsivity and a decrease in the mean time lag as the excitation and
ionization level for the species increases. Further confirmation of
photoionization predictions for broad-line gas behavior will require additional
monitoring programs for these AGNs while they are in different luminosity
states. [abridged]Comment: 37 pages, 18 figures and 15 tables, accepted for publication in the
Astrophysical Journa
The Lick AGN Monitoring Project: Photometric Light Curves and Optical Variability Characteristics
The Lick AGN Monitoring Project targeted 13 nearby Seyfert 1 galaxies with
the intent of measuring the masses of their central black holes using
reverberation mapping. The sample includes 12 galaxies selected to have black
holes with masses roughly in the range 10^6-10^7 solar masses, as well as the
well-studied AGN NGC 5548. In conjunction with a spectroscopic monitoring
campaign, we obtained broad-band B and V images on most nights from 2008
February through 2008 May. The imaging observations were carried out by four
telescopes: the 0.76-m Katzman Automatic Imaging Telescope (KAIT), the 2-m
Multicolor Active Galactic Nuclei Monitoring (MAGNUM) telescope, the Palomar
60-in (1.5-m) telescope, and the 0.80-m Tenagra II telescope. Having
well-sampled light curves over the course of a few months is useful for
obtaining the broad-line reverberation lag and black hole mass, and also allows
us to examine the characteristics of the continuum variability. In this paper,
we discuss the observational methods and the photometric measurements, and
present the AGN continuum light curves. We measure various variability
characteristics of each of the light curves. We do not detect any evidence for
a time lag between the B- and V-band variations, and we do not find significant
color variations for the AGNs in our sample.Comment: 16 pages, 20 figures, 8 tables, accepted for publication in ApJ
The Lick AGN Monitoring Project: Broad-Line Region Radii and Black Hole Masses from Reverberation Mapping of Hbeta
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7 M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission. We present here the light curves for the objects in this sample
and the subsequent Hbeta time lags for the nine objects where these
measurements were possible. The Hbeta lag time is directly related to the size
of the broad-line region, and by combining the lag time with the measured width
of the Hbeta emission line in the variable part of the spectrum, we determine
the virial mass of the central supermassive black hole in these nine AGNs. The
absolute calibration of the black hole masses is based on the normalization
derived by Onken et al. We also examine the time lag response as a function of
velocity across the Hbeta line profile for six of the AGNs. The analysis of
four leads to ambiguous results with relatively flat time lags as a function of
velocity. However, SBS 1116+583A exhibits a symmetric time lag response around
the line center reminiscent of simple models for circularly orbiting broad-line
region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most
easily explained by a simple gravitational infall model. Further investigation
will be necessary to fully understand the constraints placed on physical models
of the BLR by the velocity-resolved response in these objects.Comment: 24 pages, 16 figures and 13 tables, submitted to Ap
First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7 M_sun. We present here the first results from
this project -- the mass of the central black hole in Arp 151. Strong
variability throughout the campaign led to an exceptionally clean Hbeta lag
measurement in this object of 4.25(+0.68/-0.66) days in the observed frame.
Coupled with the width of the Hbeta emission line in the variable spectrum, we
determine a black hole mass of (7.1 +/- 1.2)x10^6 M_sun, assuming the Onken et
al. normalization for reverberation-based virial masses. We also find
velocity-resolved lag information within the Hbeta emission line which clearly
shows infalling gas in the Hbeta-emitting region. Further detailed analysis may
lead to a full model of the geometry and kinematics of broad line region gas
around the central black hole in Arp 151.Comment: 4 pages, 4 figures and 2 tables, accepted for publication in ApJ
Letter