323 research outputs found
Sudden Gravitational Transition
We investigate the properties of a cosmological scenario which undergoes a gravitational phase transition at late times. In this scenario, the Universe evolves according to general relativity in the standard, hot big bang picture until a redshift zâČ1. Nonperturbative phenomena associated with a minimally-coupled scalar field catalyzes a transition, whereby an order parameter consisting of curvature quantities such as R2, RabRab, RabcdRabcd acquires a constant expectation value. The ensuing cosmic acceleration appears driven by a dark-energy component with an equation-of-state w\u3câ1. We evaluate the constraints from type 1a supernovae, the cosmic microwave background, and other cosmological observations. We find that a range of models making a sharp transition to cosmic acceleration are consistent with observations
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
The Vulcan Photometer: A Dedicated Photometer for Extrasolar Planet Searches
A small CCD photometer dedicated to the detection of extrasolar planets has been developed and put into operation at Mount Hamilton, California. It simultaneously monitors 6000 stars brighter than 13th magnitude in its 49 deg2 field of view. Observations are conducted all night every clear night of the year. A single field is monitored at a cadence of eight images per hour for a period of about 3 months. When the data are folded for the purpose of discovering low-amplitude transits, transit amplitudes of 1% are readily detected. This precision is sufficient to find Jovian-size planets orbiting solar-like stars, which have signal amplitudes from 1% to 2% depending on the inflation of the planetâs atmosphere and the size of the star. An investigation of possible noise sources indicates that neither star field crowding, scintillation noise, nor photon shot noise are the major noise sources for stars brighter than visual magnitude 11.6. Over one hundred variable stars have been found in each star field. About 50 of these stars are eclipsing binary stars, several with transit amplitudes of only a few percent. Three stars that showed only primary transits were examined with high-precision spectroscopy. Two were found to be nearly identical stars in binary pairs orbiting at double the photometric period. Spectroscopic observations showed the third star to be a high mass ratio single-lined binary. On 1999 November 22 the transit of a planet orbiting HD 209458 was observed and the predicted amplitude and immersion times were confirmed. These observations show that the photometer and the data reduction and analysis algorithms have the necessary precision to find companions with the expected area ratio for Jovian-size planets orbiting solar-like stars
A Second Giant Planet in 3:2 Mean-Motion Resonance in the HD 204313 System
We present 8 years of high-precision radial velocity (RV) data for HD 204313
from the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The star is
known to have a giant planet (M sin i = 3.5 M_J) on a ~1900-day orbit, and a
Neptune-mass planet at 0.2 AU. Using our own data in combination with the
published CORALIE RVs of Segransan et al. (2010), we discover an outer Jovian
(M sin i = 1.6 M_J) planet with P ~ 2800 days. Our orbital fit suggests the
planets are in a 3:2 mean motion resonance, which would potentially affect
their stability. We perform a detailed stability analysis, and verify the
planets must be in resonance.Comment: Accepted for publication in Ap
A Sudden Gravitational Transition
We investigate the properties of a cosmological scenario which undergoes a
gravitational phase transition at late times. In this scenario, the Universe
evolves according to general relativity in the standard, hot Big Bang picture
until a redshift z \lesssim 1. Non-perturbative phenomena associated with a
minimally-coupled scalar field catalyzes a transition, whereby an order
parameter consisting of curvature quantities such as R^2, R_{ab}R^{ab},
R_{abcd}R^{abcd} acquires a constant expectation value. The ensuing cosmic
acceleration appears driven by a dark-energy component with an
equation-of-state w < -1. We evaluate the constraints from type 1a supernovae,
the cosmic microwave background, and other cosmological observations. We find
that a range of models making a sharp transition to cosmic acceleration are
consistent with observations.Comment: 8 pages, 8 figures; added reference
Scottish Medical Imaging Service:Technical and Governance controls
Objectives
The Scottish Medical Imaging (SMI) service provides linkable, population based, âresearch-readyâ real-world medical images for researchers to develop or validate AI algorithms within the Scottish National Safe Haven. The PICTURES research programme is developing novel methods to enhance the SMI service offering through research in cybersecurity and software/data/infrastructure engineering.
Approach
Additional technical and governance controls were required to enable safe access to medical images.
The researcher is isolated from the rest of the trusted research environment (TRE) using a Project Private Zone (PPZ). This enables researchers to build and install their own software stack, and protects the TRE from malicious code.
Guidelines are under development for researchers on the safe development of algorithms and the expected relationship between the size of the model and the training dataset. There is associated work on the statistical disclosure control of models to enable safe release of trained models from the TRE.
Results
A policy enabling the use of âNon-standard softwareâ based on prior research, domain knowledge and experience gained from two contrasting research studies was developed. Additional clauses have been added to the legal control â the eDRIS User Agreement â signed by each researcher and their Head of Department. Penalties for attempting to import or use malware, remove data within models or any attempt to deceive or circumvent such controls are severe, and apply to both the individual and their institution. The process of building and deploying a PPZ has been developed allowing researchers to install their own software.
No attempt has yet been made to add additional ethical controls; however, a future service development could be validating the performance of researchersâ algorithms on our training dataset.
Conclusion
The availability to conduct research using images poses new challenges and risks for those commissioning and operating TREs. The Private Project Zone and our associated governance controls are a huge step towards supporting the needs of researchers in the 21st century
The McDonald Observatory Planet Search: New Long-Period Giant Planets, and Two Interacting Jupiters in the HD 155358 System
We present high-precision radial velocity (RV) observations of four
solar-type (F7-G5) stars - HD 79498, HD 155358, HD 197037, and HD 220773 -
taken as part of the McDonald Observatory Planet Search Program. For each of
these stars, we see evidence of Keplerian motion caused by the presence of one
or more gas giant planets in long-period orbits. We derive orbital parameters
for each system, and note the properties (composition, activity, etc.) of the
host stars. While we have previously announced the two-gas-giant HD 155358
system, we now report a shorter period for planet c. This new period is
consistent with the planets being trapped in mutual 2:1 mean-motion resonance.
We therefore perform an in-depth stability analysis, placing additional
constraints on the orbital parameters of the planets. These results demonstrate
the excellent long-term RV stability of the spectrometers on both the Harlan J.
Smith 2.7 m telescope and the Hobby-Eberly telescope.Comment: 38 pages, 10 figures, 6 tables. Accepted for publication in Ap
A 12-year activity cycle for the nearby planet host star HD 219134
The nearby (6.5 pc) star HD 219134 was recently shown by Motalebi et al. and Vogt et al. to host several planets,
the innermost of which is transiting. We present 27 years of radial velocity (RV) observations of this star from the McDonald Observatory Planet Search program, and 19 years of stellar activity data. We detect a long-period
activity cycle measured in the Ca II SHK index, with a period of 4230±100 days (11.7 years), very similar to the 11 year solar activity cycle. Although the period of the Saturn-mass planet HD 219134 h is close to half that of the activity cycle, we argue that it is not an artifact due to stellar activity. We also find a significant periodicity in the SHK data due to stellar rotation with a period of 22.8 days. This is identical to the period of planet f identified by Vogt et al., suggesting that this RV signal might be caused by rotational modulation of stellar activity rather than a
planet. Analysis of our RVs allows us to detect the long-period planet HD 219134 h and the transiting super-Earth
HD 219134 b. Finally, we use our long time baseline to constrain the presence of longer period planets in the
system, excluding to 1s objects with M sin i > 0.36MJ at 12 years (corresponding to the orbital period of Jupiter)
and M sin i > 0.72MJ at a period of 16.4 years (assuming a circular orbit for an outer companion)
Hectospec, the MMT's 300 Optical Fiber-Fed Spectrograph
The Hectospec is a 300 optical fiber fed spectrograph commissioned at the MMT
in the spring of 2004. A pair of high-speed six-axis robots move the 300 fiber
buttons between observing configurations within ~300 s and to an accuracy ~25
microns. The optical fibers run for 26 m between the MMT's focal surface and
the bench spectrograph operating at R~1000-2000. Another high dispersion bench
spectrograph offering R~5,000, Hectochelle, is also available. The system
throughput, including all losses in the telescope optics, fibers, and
spectrograph peaks at ~10% at the grating blaze in 1" FWHM seeing. Correcting
for aperture losses at the 1.5" diameter fiber entrance aperture, the system
throughput peaks at 17%. Hectospec has proven to be a workhorse
instrument at the MMT. Hectospec and Hectochelle together were scheduled for
1/3 of the available nights since its commissioning. Hectospec has returned
\~60,000 reduced spectra for 16 scientific programs during its first year of
operation.Comment: 68 pages, 28 figures, to appear in December 2005 PAS
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