155 research outputs found
A New Z=0 Metagalactic Ultraviolet Background Limit
We present new integral-field spectroscopy in the outskirts of two nearby, edge-on, late-type galaxies to search for the H alpha emission that is expected from the exposure of their hydrogen gas to the metagalactic ultraviolet background (UVB). Despite the sensitivity of the VIRUS-P spectrograph on the McDonald 2.7 m telescope to low surface brightness emission and the large field of view, we do not detect H alpha to 5 sigma upper limits of 6.4 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 7321 and of 25 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 1281 in each of the hundreds of independent spatial elements (fibers). We fit gas distribution models from overlapping 21 cm data of HI, extrapolate one scale length beyond the HI data, and estimate predicted H alpha surface brightness maps. We analyze three types of limits from the data with stacks formed from increasingly large spatial regions and compare to the model predictions: (1) single fibers, (2) convolution of the fiber grid with a Gaussian, circular kernel (10('') full width at half-maximum), and (3) the co-added spectra from a few hundred fibers over the brightest model regions. None of these methods produce a significant detection (>5 sigma) with the most stringent constraints on the Hi photoionization rate of Gamma(z = 0) < 1.7 x 10(-14) s(-1) in UGC 7321 and Gamma(z = 0) < 14 x 10(-14) s(-1) in UGC 1281. The UGC 7321 limit is below previous measurement limits and also below current theoretical models. Restricting the analysis to the fibers bound by the HI data leads to a comparable limit; the limit is Gamma(z = 0) < 2.3 x 10(-14) s(-1) in UGC 7321. We discuss how a low Lyman limit escape fraction in z similar to 0 redshift star-forming galaxies might explain this lower than predicted UVB strength and the prospects of deeper data to make a direct detection.U.S. Government NAG W-2166National Science FoundationUT David BrutonTexas Norman Hackerman Advanced Research Program 003658-0295-2007Cynthia and George Mitchell FoundationMcDonald Observator
Secretly Eccentric: The Giant Planet and Activity Cycle of GJ 328
We announce the discovery of a ~2 Jupiter-mass planet in an eccentric 11-year
orbit around the K7/M0 dwarf GJ 328. Our result is based on 10 years' worth of
radial velocity (RV) data from the Hobby-Eberly and Harlan J. Smith telescopes
at McDonald Observatory, and from the Keck Telescope at Mauna Kea. Our analysis
of GJ 328's magnetic activity via the Na I D features reveals a long-period
stellar activity cycle, which creates an additional signal in the star's RV
curve with amplitude 6-10 m/s. After correcting for this stellar RV
contribution, we see that the orbit of the planet is more eccentric than
suggested by the raw RV data. GJ 328b is currently the most massive,
longest-period planet discovered around a low-mass dwarf.Comment: Accepted for publication in Ap
B2 0902+34: A Collapsing Protogiant Elliptical Galaxy at z=3.4
We have used the visible integral-field replicable unit spectrograph
prototype (VIRUS-P), a new integral field spectrograph, to study the spatially
and spectrally resolved Lyman-alpha emission line structure in the radio galaxy
B2 0902+34 at z=3.4. We observe a halo of Lyman-alpha emission with a velocity
dispersion of 250 km/s extending to a radius of 50 kpc. A second feature is
revealed in a spatially resolved region where the line profile shows
blueshifted structure. This may be viewed as either HI absorption at -450 km/s
or secondary emission at -900 km/s from the primary peak. Our new data, in
combination with the 21 cm absorption, suggest two important and unexplained
discrepancies. First, nowhere in the line profiles of the Lyman-alpha halo is
the 21 cm absorber population evident. Second, the 21 cm absorption redshift is
higher than the Lyman-alpha emission redshift. In an effort to explain these
two traits, we have undertaken the first three dimensional Monte Carlo
simulations of resonant scattering in radio galaxies. Though simple, the model
produces the features in the Lyman-alpha data and predicts the 21 cm
properties. To reach agreement between this model and the data, global infall
of the HI is strictly necessary. The amount of gas necessary to match the model
and data is surprisingly high, >= 10E12 solar masses, an order of magnitude
larger than the stellar mass. The collapsing structure and large gas mass lead
us to interpret B2 0902+34 as a protogiant elliptical galaxy.Comment: 30 pages, 8 figures, 4 tables, accepted in Ap
Stellar Activity and its Implications for Exoplanet Detection on GJ 176
We present an in-depth analysis of stellar activity and its effects on radial
velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10 years from
the High Resolution Spectrograph on the Hobby-Eberly Telescope. These data are
supplemented with spectra from previous observations with the HIRES and HARPS
spectrographs, and V- and R-band photometry taken over 6 years at the Dyer and
Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth
exoplanet in an 8.8-day orbit. However, the velocities of this star are also
known to be contaminated by activity, particularly at the 39-day stellar
rotation period. We have examined the magnetic activity of GJ 176 using the
sodium I D lines, which have been shown to be a sensitive activity tracer in
cool stars. In addition to rotational modulation, we see evidence of a
long-term trend in our Na I D index, which may be part of a long-period
activity cycle. The sodium index is well correlated with our RVs, and we show
that this activity trend drives a corresponding slope in RV. Interestingly, the
rotation signal remains in phase in photometry, but not in the spectral
activity indicators. We interpret this phenomenon as the result of one or more
large spot complexes or active regions which dominate the photometric
variability, while the spectral indices are driven by the overall magnetic
activity across the stellar surface. In light of these results, we discuss the
potential for correcting activity signals in the RVs of M dwarfs.Comment: Accepted for publication in Ap
Revisiting rho 1 Cancri e: A New Mass Determination Of The Transiting super-Earth
We present a mass determination for the transiting super-Earth rho 1 Cancri e
based on nearly 700 precise radial velocity (RV) measurements. This extensive
RV data set consists of data collected by the McDonald Observatory planet
search and published data from Lick and Keck observatories (Fischer et al.
2008). We obtained 212 RV measurements with the Tull Coude Spectrograph at the
Harlan J. Smith 2.7 m Telescope and combined them with a new Doppler reduction
of the 131 spectra that we have taken in 2003-2004 with the
High-Resolution-Spectrograph (HRS) at the Hobby-Eberly Telescope (HET) for the
original discovery of rho 1 Cancri e. Using this large data set we obtain a
5-planet Keplerian orbital solution for the system and measure an RV
semi-amplitude of K = 6.29 +/- 0.21 m/s for rho 1 Cnc e and determine a mass of
8.37 +/- 0.38 M_Earth. The uncertainty in mass is thus less than 5%. This
planet was previously found to transit its parent star (Winn et al. 2011,
Demory et al. 2011), which allowed them to estimate its radius. Combined with
the latest radius estimate from Gillon et al. (2012), we obtain a mean density
of rho = 4.50 +/- 0.20 g/cm^3. The location of rho 1 Cnc e in the mass-radius
diagram suggests that the planet contains a significant amount of volitales,
possibly a water-rich envelope surrounding a rocky core.Comment: 16 pages, 5 figures, accepted for publication in the Astrophysical
Journal (the 300+ RV measurements will be published as online tables or can
be obtained from the author
Radial Velocity Observations and Light Curve Noise Modeling Confirm That Kepler-91b is a Giant Planet Orbiting a Giant Star
Kepler-91b is a rare example of a transiting hot Jupiter around a red giant
star, providing the possibility to study the formation and composition of hot
Jupiters under different conditions compared to main-sequence stars. However,
the planetary nature of Kepler-91b, which was confirmed using phase-curve
variations by Lillo-Box et al., was recently called into question based on a
re-analysis of Kepler data. We have obtained ground-based radial velocity
observations from the Hobby-Eberly Telescope and unambiguously confirm the
planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial
velocity data. The star exhibits temporally correlated noise due to stellar
granulation which we model as a Gaussian Process. We hypothesize that it is
this noise component that led previous studies to suspect Kepler-91b to be a
false positive. Our work confirms the conclusions presented by Lillo-Box et al.
that Kepler-91b is a 0.73+/-0.13 Mjup planet orbiting a red giant star.Comment: Published in Ap
A Dedicated M-Dwarf Planet Search Using The Hobby-Eberly Telescope
We present first results of our planet search program using the 9.2 meter
Hobby-Eberly Telescope (HET) at McDonald Observatory to detect planets around
M-type dwarf stars via high-precision radial velocity (RV) measurements.
Although more than 100 extrasolar planets have been found around solar-type
stars of spectral type F to K, there is only a single M-dwarf (GJ 876, Delfosse
et al. 1998; Marcy et al. 1998; Marcy et al. 2001) known to harbor a planetary
system. With the current incompleteness of Doppler surveys with respect to
M-dwarfs, it is not yet possible to decide whether this is due to a fundamental
difference in the formation history and overall frequency of planetary systems
in the low-mass regime of the Hertzsprung-Russell diagram, or simply an
observational bias. Our HET M-dwarf survey plans to survey 100 M-dwarfs in the
next 3 to 4 years with the primary goal to answer this question. Here we
present the results from the first year of the survey which show that our
routine RV-precision for M-dwarfs is 6 m/s. We found that GJ 864 and GJ 913 are
binary systems with yet undetermined periods, while 5 out of 39 M-dwarfs reveal
a high RV-scatter and represent candidates for having short-periodic planetary
companions. For one of them, GJ 436 (rms = 20.6 m/s), we have already obtained
follow-up observations but no periodic signal is present in the RV-data.Comment: 12 pages, 14 figures, accepted for publication in the Astronomical
Journa
The Influence of Motion and Stress on Optical Fibers
We report on extensive testing carried out on the optical fibers for the
VIRUS instrument. The primary result of this work explores how 10+ years of
simulated wear on a VIRUS fiber bundle affects both transmission and focal
ratio degradation (FRD) of the optical fibers. During the accelerated lifetime
tests we continuously monitored the fibers for signs of FRD. We find that
transient FRD events were common during the portions of the tests when motion
was at telescope slew rates, but dropped to negligible levels during rates of
motion typical for science observation. Tests of fiber transmission and FRD
conducted both before and after the lifetime tests reveal that while
transmission values do not change over the 10+ years of simulated wear, a clear
increase in FRD is seen in all 18 fibers tested. This increase in FRD is likely
due to microfractures that develop over time from repeated flexure of the fiber
bundle, and stands in contrast to the transient FRD events that stem from
localized stress and subsequent modal diffusion of light within the fibers.
There was no measurable wavelength dependence on the increase in FRD over 350
nm to 600 nm. We also report on bend radius tests conducted on individual
fibers and find the 266 microns VIRUS fibers to be immune to bending-induced
FRD at bend radii of R > 10cm. Below this bend radius FRD increases slightly
with decreasing radius. Lastly, we give details of a degradation seen in the
fiber bundle currently deployed on the Mitchell Spectrograph (formally VIRUS-P)
at McDonald Observatory. The degradation is shown to be caused by a localized
shear in a select number of optical fibers that leads to an explosive form of
FRD. In a few fibers, the overall transmission loss through the instrument can
exceed 80%.Comment: 19 pages, 22 figure
The VIRUS-P Exploration of Nearby Galaxies (VENGA): Survey Design and First Results
VENGA is a large-scale extragalactic IFU survey, which maps the bulges, bars
and large parts of the outer disks of 32 nearby normal spiral galaxies. The
targets are chosen to span a wide range in Hubble types, star formation
activities, morphologies, and inclinations, at the same time of having vast
available multi-wavelength coverage from the far-UV to the mid-IR, and
available CO and 21cm mapping. The VENGA dataset will provide 2D maps of the
SFR, stellar and gas kinematics, chemical abundances, ISM density and
ionization states, dust extinction and stellar populations for these 32
galaxies. The uniqueness of the VIRUS-P large field of view permits these
large-scale mappings to be performed. VENGA will allow us to correlate all
these important quantities throughout the different environments present in
galactic disks, allowing the conduction of a large number of studies in star
formation, structure assembly, galactic feedback and ISM in galaxies.Comment: 7 pages, 3 figures, proceedings of the "Third Biennial Frank N. Bash
Symposium, New Horizons in Astronomy" held in Austin, TX, Oct. 2009. To be
published in the Astronomical Society of the Pacific Conference Series, eds.
L. Stanford, L. Hao, Y. Mao, J. Gree
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