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Jeff A. Valenti

Bio: Jeff A. Valenti is an academic researcher from Space Telescope Science Institute. The author has contributed to research in topics: Stars & T Tauri star. The author has an hindex of 25, co-authored 49 publications receiving 5339 citations. Previous affiliations of Jeff A. Valenti include University of Texas at Austin & University of Hawaii.
Topics: Stars, T Tauri star, Planet, Exoplanet, Spectral line

Papers
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K. C. Chambers, E. A. Magnier, Nigel Metcalfe, H. Flewelling, M. E. Huber, Christopher Waters, L. Denneau, Peter W. Draper, Daniel J. Farrow, D. P. Finkbeiner, C. Holmberg, J. Koppenhoefer, P. A. Price, A. Rest, Roberto P. Saglia, Edward F. Schlafly, Stephen J. Smartt, W. E. Sweeney, R. J. Wainscoat, W. S. Burgett, S. Chastel, T. Grav, J. N. Heasley, Klaus W. Hodapp, Robert Jedicke, Nick Kaiser, R. P. Kudritzki, G. A. Luppino, Robert H. Lupton, David G. Monet, John Morgan, Peter M. Onaka, Bernie Shiao, Christopher W. Stubbs, John L. Tonry, R. L. White, Eduardo Bañados, Eric F. Bell, Ralf Bender, Edouard J. Bernard, M. Boegner, F. Boffi, M. T. Botticella, Annalisa Calamida, Stefano Casertano, W.-P. Chen, X. Chen, Shaun Cole, Niall R. Deacon, C. Frenk, Alan Fitzsimmons, Suvi Gezari, V. Gibbs, C. Goessl, T. Goggia, R. Gourgue, Bertrand Goldman, Phillip Grant, Eva K. Grebel, Nigel Hambly, G. Hasinger, Alan Heavens, Timothy M. Heckman, Robert Henderson, Th. Henning, M. J. Holman, Ulrich Hopp, Wing-Huen Ip, S. Isani, M. Jackson, C. D. Keyes, Anton M. Koekemoer, Rubina Kotak, D. Le, D. Liska, K. S. Long, John R. Lucey, M. Liu, Nicolas F. Martin, G. Masci, Brian McLean, E. Mindel, P. Misra, E. Morganson, David Murphy, A. Obaika, Gautham Narayan, M. Nieto-Santisteban, Peder Norberg, John A. Peacock, E. A. Pier, Marc Postman, N. Primak, C. Rae, A. Rai, Adam G. Riess, A. Riffeser, H. W. Rix, Siegfried Röser, R. Russel, L. Rutz, Elena Schilbach, A. S. B. Schultz, Daniel Scolnic, Louis Gregory Strolger, Alexander S. Szalay, Stella Seitz, E. Small, K. W. Smith, D. R. Soderblom, P. Taylor, Robert R. Thomson, Andy Taylor, A. R. Thakar, J. Thiel, D. A. Thilker, D. Unger, Yuji Urata, Jeff A. Valenti, J. Wagner, T. Walder, Fabian Walter, S. Watters, S. Werner, W. M. Wood-Vasey, R. F. G. Wyse 
TL;DR: Pan-STARRS1 has carried out a set of distinct synoptic imaging sky surveys including the 3ππ$ Steradian Survey and the Medium Deep Survey in 5 bands as mentioned in this paper.
Abstract: Pan-STARRS1 has carried out a set of distinct synoptic imaging sky surveys including the $3\pi$ Steradian Survey and the Medium Deep Survey in 5 bands ($grizy_{P1}$). The mean 5$\sigma$ point source limiting sensitivities in the stacked 3$\pi$ Steradian Survey in $grizy_{P1}$ are (23.3, 23.2, 23.1, 22.3, 21.4) respectively. The upper bound on the systematic uncertainty in the photometric calibration across the sky is 7-12 millimag depending on the bandpass. The systematic uncertainty of the astrometric calibration using the Gaia frame comes from a comparison of the results with Gaia: the standard deviation of the mean and median residuals ($ \Delta ra, \Delta dec $) are (2.3, 1.7) milliarcsec, and (3.1, 4.8) milliarcsec respectively. The Pan-STARRS system and the design of the PS1 surveys are described and an overview of the resulting image and catalog data products and their basic characteristics are described together with a summary of important results. The images, reduced data products, and derived data products from the Pan-STARRS1 surveys are available to the community from the Mikulski Archive for Space Telescopes (MAST) at STScI.

1,257 citations

Journal ArticleDOI
TL;DR: In this article, a nonlinear least squares algorithm is used to solve for any subset of allowed parameters, which include atomic data (loggf and van der Waals damping constants), model atmosphere specications (Te,l og g), elemental abundances, and radial, turbulent, and rotational velocities.
Abstract: We describe a new software package that may be used to determine stellar and atomic parameters by matching observed spectra with synthetic spectra generated from parameterized atmospheres. A nonlinear least squares algorithm is used to solve for any subset of allowed parameters, which include atomic data (loggf and van der Waals damping constants), model atmosphere specications (Te ,l og g), elemental abundances, and radial, turbulent, and rotational velocities. LTE synthesis software handles discontiguous spectral intervals and complex atomic blends. As a demonstration, we t 26 Fe I lines in the NSO Solar Atlas (Kurucz et al. 1984), determining various solar and atomic parameters.

896 citations

Journal ArticleDOI
TL;DR: In this paper, the mass of the star HD 149026 was derived based on interpolation of stellar evolutionary models and the Doppler amplitude, K=43.3 m s^-1, and orbital radius of 0.042 AU.
Abstract: Doppler measurements from Subaru and Keck have revealed radial velocity variations in the V=8.15, G0IV star HD 149026 consistent with a Saturn-Mass planet in a 2.8766 day orbit. Photometric observations at Fairborn Observatory have detected three complete transit events with depths of 0.003 mag at the predicted times of conjunction. HD 149026 is now the second brightest star with a transiting extrasolar planet. The mass of the star, based on interpolation of stellar evolutionary models, is 1.3 +/- 0.1 solar masses; together with the Doppler amplitude, K=43.3 m s^-1, we derive a planet mass Msin(i)=0.36 Mjup, and orbital radius of 0.042 AU. HD 149026 is chromospherically inactive and metal-rich with spectroscopically derived [Fe/H]=+0.36, Teff=6147 K, log g=4.26 and vsin(i)=6.0 km s^-1. Based on Teff and the stellar luminosity of 2.72 Lsun, we derive a stellar radius of 1.45 Rsun. Modeling of the three photometric transits provides an orbital inclination of 85.3 +/- 1.0 degrees and (including the uncertainty in the stellar radius) a planet radius of 0.725 +/- 0.05 Rjup. Models for this planet mass and radius suggest the presence of a ~67 Mearth core composed of elements heavier than hydrogen and helium. This substantial planet core would be difficult to construct by gravitational instability.

347 citations

Journal ArticleDOI
TL;DR: The database is described in detail, including the construction of the database, the provenance of the data, the schema, and how the database tables are related.
Abstract: This paper describes the organization of the database and the catalog data products from the Pan-STARRS1 $3\pi$ Steradian Survey. The catalog data products are available in the form of an SQL-based relational database from MAST, the Mikulski Archive for Space Telescopes at STScI. The database is described in detail, including the construction of the database, the provenance of the data, the schema, and how the database tables are related. Examples of queries for a range of science goals are included. The catalog data products are available in the form of an SQL-based relational database from MAST, the Mikulski Archive for Space Telescopes at STScI.

315 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined several theories that describe how stellar magnetic fields on T T Tauri stars interact with their surrounding accretion disks, and demonstrated that these theories require magnetic field strengths ranging from a few hundred to several thousand gauss, depending on which model is used and more importantly on the properties of individual systems.
Abstract: We examine several theories that describe how stellar magnetic fields on classical T Tauri stars (CTTSs) interact with their surrounding accretion disks. We demonstrate that these theories require magnetic field strengths ranging from a few hundred to several thousand gauss, depending on which model is used and more importantly on the properties of individual systems. For example, the CTTS BP Tau is predicted to have a relatively strong magnetic field (1.4-4.1 kG), which should be detectable. We present infrared (IR) and optical echelle spectra of BP Tau and several reference stars of similar spectral class. Using detailed spectrum synthesis and the latest model atmospheres, we fitted 12 absorption features in the optical spectrum, including the strong titanium oxide (TiO) band head at 7055 A. For BP Tau we determine key stellar parameters: effective temperature (Teff=4055 ± 112 K), gravity (log g=3.67 ± 0.50), metallicity ([M/H]=0.18 ± 0.11), projected rotational velocity (v sin i=10.2 ± 1.8 km s-1), and optical veiling (r=0.00-0.15). A similar analysis of 61 Cyg B (K7 V) is used to validate the methodology. We then use the IR spectra to look for Zeeman broadening, which has a more pronounced effect at longer wavelengths. A Zeeman sensitive Ti I line at 2.2233 μm appears significantly broadened in BP Tau, relative to several rotationally broadened standard stars. The observed line is also significantly broader than predictions based on our optical analysis. Interpreting this excess broadening as Zeeman splitting of the Ti I line, we fitted the spectrum and find a distribution of field strengths whose surface averaged mean is =2.6 ± 0.3 kG. We did not use the Zeeman sensitive Fe I line at 8468.4 A when determining stellar or magnetic parameters for BP Tau, so this line provides a test of our results. The observed line profile is indeed broader than the nonmagnetic prediction, but the 8468.4 A line gives a magnetic flux lower than what was obtained in the IR, perhaps indicating that strong fields are concentrated into cool spots. Finally, we investigate an ad hoc model in which the IR line is assumed to form in the accretion disk itself. We discuss several reasons why the magnetic model is preferred, but the disk atmosphere example illustrates that our magnetic field measurement must still be tested using several IR lines with a range of Zeeman sensitivities.

289 citations


Cited by
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TL;DR: The second Gaia data release, Gaia DR2 as mentioned in this paper, is a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products.
Abstract: Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims: A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods: The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results: Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the GBP (330-680 nm) and GRP (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions: Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.

8,308 citations

Journal ArticleDOI
TL;DR: In this article, a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors.
Abstract: On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim$1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg$^2$ at a luminosity distance of $40^{+8}_{-8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Msun. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim$40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over $\sim$10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position $\sim$9 and $\sim$16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. (Abridged)

3,180 citations

Journal ArticleDOI
TL;DR: Modules for Experiments in Stellar Astrophysics (MESA) as discussed by the authors is an open source software package for modeling the evolution of stellar structures and composition. But it is not suitable for large-scale systems such as supernovae.
Abstract: We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ? stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results.

2,761 citations

Journal ArticleDOI
TL;DR: In this article, an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, is presented.
Abstract: Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. Methods. The most recent version of the MARCS program is used. Results. We present a grid of about 104 model atmospheres for stars with 2500K <= T-eff <= 8000 K, -1 <= log g = log (GM/R-2) <= 5 (cgs) with various masses and radii, -5 <= [Me/H] <= + 1, with [alpha/Fe] = 0.0 and 0.4 and different choices of C and N abundances. This includes "CN-cycled" models with C/N=4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 <= xi(t) = 5km s(-1). We also list thermodynamic quantities (T, P-g, P-e, rho, partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with planeparallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate "rules of thumb" concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.

2,411 citations

Journal ArticleDOI
TL;DR: In this paper, the authors identify a subset of 850 stars that have Doppler observations sufficient to detect uniformly all planets with radial velocity semiamplitudes K > 30 m s-1 and orbital periods shorter than 4 yr, and determine that fewer than 3% of stars with -0.5 + 0.3 dex, 25% of observed stars have detected gas giant planets.
Abstract: We have recently carried out spectral synthesis modeling to determine Teff, log g, v sin i, and [Fe/H] for 1040 FGK-type stars on the Keck, Lick, and Anglo-Australian Telescope planet search programs. This is the first time that a single, uniform spectroscopic analysis has been made for every star on a large Doppler planet search survey. We identify a subset of 850 stars that have Doppler observations sufficient to detect uniformly all planets with radial velocity semiamplitudes K > 30 m s-1 and orbital periods shorter than 4 yr. From this subset of stars, we determine that fewer than 3% of stars with -0.5 +0.3 dex, 25% of observed stars have detected gas giant planets. A power-law fit to these data relates the formation probability for gas giant planets to the square of the number of metal atoms. High stellar metallicity also appears to be correlated with the presence of multiple-planet systems and with the total detected planet mass. This data set was examined to better understand the origin of high metallicity in stars with planets. None of the expected fossil signatures of accretion are observed in stars with planets relative to the general sample: (1) metallicity does not appear to increase as the mass of the convective envelopes decreases, (2) subgiants with planets do not show dilution of metallicity, (3) no abundance variations for Na, Si, Ti, or Ni are found as a function of condensation temperature, and (4) no correlations between metallicity and orbital period or eccentricity could be identified. We conclude that stars with extrasolar planets do not have an accretion signature that distinguishes them from other stars; more likely, they are simply born in higher metallicity molecular clouds.

1,624 citations