Guillermo Torres - Academia.edu (original) (raw)

Papers by Guillermo Torres

We report new spectroscopic observations of the recently discovered transiting planet OGLE-TR-56b... more We report new spectroscopic observations of the recently discovered transiting planet OGLE-TR-56b with the Keck/HIRES instrument. Our radial velocity measurements with errors of ~100 m/s show clear variations that are in excellent agreement with the phasing (period and epoch) derived from the OGLE transit photometry, confirming the planetary nature of the companion. The new data combined with measurements from the previous season allow an improved determination of the mass of the planet, M_p = 1.45 +/- 0.23 M_Jup. All available OGLE photometry, including new measurements made this season, have also been analyzed to derive an improved value for the planetary radius of R_p = 1.23 +/- 0.16 R_Jup. We discuss the implications of these results for the theory of extrasolar planets.

Bulletin of the American Astronomical Society, May 1, 2005

As a part of a larger program to measure physical properties of PMS binary systems, we have obser... more As a part of a larger program to measure physical properties of PMS binary systems, we have observed the quadruple system HD 98800 with the Keck Interferometer (KI), and resolved the two separate spectroscopic binary components of the system. In particular we have observed the North (B) binary component on multiple epochs, and integrating our data with the double-lined spectroscopic orbit from Torres et al 1995 has allowed us to estimate a provisional physical orbit for the B system. This orbit in turn yields relatively accurate (5 independent system distance and component luminosity estimates. Our orbital solution favors a high-inclination orientation for the orbit, suggesting that both components of the HD 98800 B system are under 0.6 Msolar. Comparisons between the estimated physical parameters for the HD 98800 B components with mass-luminosity models of PMS stars will be discussed.

Bulletin of the American Astronomical Society, 2010

The extremely interesting detection of transiting Super-Earth planets is now in range of Space su... more The extremely interesting detection of transiting Super-Earth planets is now in range of Space surveys (CoRoT & Kepler), but is a very challenging case for confirmation by radial velocity facilities. The high photometric precision of CoRoT and Kepler allows to explore the range of stellar blend scenarios that might fit the data equally well as a planet model. Unless the effective temperature of the contaminating star is virtually identical to that of the parent star (within 50 K), the depth of the photometric signal will be wavelength dependent. With its long wavelength bandpasses and high photometric precision, Spitzer is ideal to test this possibility, and potentially confirm the planetary nature of Super-Earth candidates. We present the results of our study of CoRoT-7b, the first such case, in the Spitzer IRAC 4.5 and 8 microns bandpasses.

Astrophys J, 1997

We report new spectroscopic observations of the close binaries θ 1 Tauri and θ 2 Tauri in the Hya... more We report new spectroscopic observations of the close binaries θ 1 Tauri and θ 2 Tauri in the Hyades. Our radial velocities for the primary component of θ 1 Tau, supplemented with other velocities from the literature and existing astrometric information (speckle ...

Bulletin of the American Astronomical Society, Feb 27, 1995

We report on a search for weak-line T Tauri stars (wTTS) in the vicinity of the Taurus--Auriga st... more We report on a search for weak-line T Tauri stars (wTTS) in the vicinity of the Taurus--Auriga star forming region. For ground-based optical follow-up observations we have selected unidentified X-ray sources from the ROSAT All-Sky Survey. So far, we have performed high-resolution spectroscopy with CfA-echelle-spectrographs for 109 unidentified X-ray sources south of the Taurus molecular clouds in order to measure their radial velocity to test kinematic membership to Taurus. Additional mid-resolution spectra obtained for 40 sources so far show that 15 of them have spectra typical of wTTS, exhibiting weak H alpha emission and Lithium 6708 Angstroms absorption. Seven of these new wTTS have radial velocities between 13 and 21 km/s, i.e. consistent with membership to Taurus. Hence, the Taurus--Auriga star forming region seems to extend much further south than previously assumed. These new TTS lie far from regions of ongoing star formation, and it is not clear whether they were formed in clouds cores in central Taurus and moved to their present locations, or whether they were formed near their present locations. We plan to extend the search to find the borders of the Taurus T association. All TTS known in Taurus prior to the ROSAT mission are located in or near molecular clouds, namely in an area given by 4 h <= alpha <= 5 h and 14(deg) <= delta <= 35(deg) . The region we plan to study surrounds this central Taurus region by 10 deg wide strips.

Cool Stars Stellar Systems and the Sun, 1998

We have obtained single-order echelle spectra for 106 late-type stars found with ROSAT south of T... more We have obtained single-order echelle spectra for 106 late-type stars found with ROSAT south of Taurus, including some 30 stars that have been claimed to be low-mass pre-main sequence (PMS) stars. 19 stars are located on the Lambda Ori cloud, nine of which are K-type stars with lithium in excess of the zero-age-main-sequence (ZAMS) level; i.e., are PMS stars. At least 40 of the remaining off-cloud stars display detectable lithium, 24 of which show lithium at least as strong as IC 2602 stars with the same spectral types and, therefore, are probably not older than IC 2602 (~3 x 10^7 yr). Of those 24 stars, nine (25% of the off-cloud stars with detectable lithium) are PMS stars isolated from cloud material; all have spectral type K, and three of them are spectroscopic binaries. The remaining 15 off-cloud stars have spectral type G and lithium comparable to IC 2602 stars, i.e., may have arrived already on the ZAMS, as the G-type IC 2602 stars have. However, these 24 off-cloud lithium-excess stars are probably not older than IC 2602 (~3 x 10^7 yr). For 18 of the lithium-excess stars south of Taurus, we have determined proper motions with a typical accuracy of 5 mas/yr from the STARNET catalog, a combination of the HST GSC1.2 and the Astrographic Catalog. Most of these 18 stars have spectral type G. Their 3D space velocity is different from the 3D velocity distribution of bona-fide T Tauri stars in central Taurus. We conclude that the new G-type stars among the lithium-excess population may be young Gould Belt members. Since both the GSC and the AC are magnitude-limited, only the brightest stars (i.e., the G-type stars) are listed in STARNET. Run-away T Tauri stars, however, should be most frequent among lower-mass stars. We also discuss alternative modes of origin of the isolated PMS stars south of Taurus.

Astronomy and Astrophysics, Feb 15, 2010

Astronomy and Astrophysics, May 30, 1998

International Astronomical Union Colloquium, 1999

NGC 6334 is one of the most active massive star forming regions in the Galaxy. Located at a dista... more NGC 6334 is one of the most active massive star forming regions in the Galaxy. Located at a distance of 1.74 kpc, this giant molecular cloud extends for more than 45 arcmin parallel to the galactic plane. Recent near IR observations of the region indicate the presence of young low mass stars, while the formation of high mass stars has been documented in clusters along a narrow ridge within the molecular cloud. We propose deep Spitzer observation of the region with IRAC in all 4 bands. These observations will allow us to study star formation in NGC 6334 at the low mass end of the mass function, and, combined with MIPSGAL data at 24 and 70 um, to search for embedded protostars. Previous shallow observations obtained as part if the GLIMPSE survey are not sensitive enough for this kind of study.

Astronomy and Astrophysics, Jun 29, 1995

We report on the discovery of 15 new weak-line T Tauri stars (wTTS) south of the Taurus molecular... more We report on the discovery of 15 new weak-line T Tauri stars (wTTS) south of the Taurus molecular clouds based on the large database produced by the ROSAT All-Sky Survey. High-resolution spectroscopy of 109 optical counterparts of X-ray sources has been performed to measure their radial velocities in order to verify kinematic membership to the Taurus T association. Using additional mid-resolution spectroscopy of 44 sources we find that 15 stars exhibit TTS characteristics such as weak Hα emission, Li 6708A absorption. and late spectral types. On the basis of their Lithium abundance we suspect hat these 15 new wTTS are relatively young. Seven of them have radial velocities between 12 and 21km/s, i.e. consistent with previously known TTS in Taurus molecular clouds, while other new wTTS lie up to 50pc away from regions of ongoing star formation and have radial velocities far off the mean Taurus velocity. The region populated by wTTS in the direction of Taurus extends much further south than previously assumed.

We present an analysis of three years of precision radial velocity measurements of 160 metal-poor... more We present an analysis of three years of precision radial velocity measurements of 160 metal-poor stars observed with Keck/HIRES. We report on variability and long-term velocity trends for each star in our sample. We identify several long-term, low-amplitude radial-velocity variables worthy of follow-up with direct imaging techniques. We place lower limits on the detectable companion mass as a function of orbital period. None of the stars in our sample exhibits radial-velocity variations compatible with the presence of Jovian planets with periods shorter than the survey duration (3 yr). The resulting average frequency of gas giants orbiting metal-poor dwarfs with -2.0≲[Fe/H]≲ -0.6 is f_p<0.67%. By combining our dataset with the Fischer & Valenti (2005) uniform sample, we confirm that the likelihood of a star to harbor a planet more massive than Jupiter within 2 AU is a steeply rising function of the host's metallicity. However, the data for stars with -1.0≲[Fe/H]≲ 0.0 are compatible, in a statistical sense, with a constant occurrence rate f_p≃1%. Our results usefully inform theoretical studies of the process of giant planet formation across two orders of magnitude in metallicity.

Transiting Extrapolar Planets Workshop, Jul 1, 2007

The TrES project is designed to search for exoplanetary transits using three wide-field optical t... more The TrES project is designed to search for exoplanetary transits using three wide-field optical telescopes of 10-cm in diameter, in three different observatories. We describe the instruments and strategies used by the team, which has been working as a network since 2003. We summarize the major findings and difficulties faced during these years, which include the discovery of two transiting planets, a pair of eclipsing M stars, and many configurations of stars that mimic the signal of transiting planets.

Revista Facultad De Odontologia Universidad De Antioquia, Dec 2, 2010

Bulletin of the American Astronomical Society, 2009

The Radial Velocity technique has been the most successful method for detecting extrasolar planet... more The Radial Velocity technique has been the most successful method for detecting extrasolar planets. It has revealed the frequency and orbital characteristics of planets around nearby stars, providing valuable constraints for theories of planetary formation, migration, and evolution. Radial velocities play key supporting roles for space missions to detect planets by astrometric means and by the transit technique. The technique will provide targets for JWST, as well as for imaging missions in the next decade. The 2008 Exoplanet Forum Committee on Radial Velocities supports the conclusion of the Exoplanet Task Force Report that it is critical to make progress in the precision of the velocities in the next few years to enable the detection and characterization of terrestrial planets, both in the optical and in the near infrared. This will involve not only improving the wavelength reference, but also understanding other sources of noise of astrophysical origin. Specific efforts toward this goal are proposed. The Committee has identified the lack of access to telescope time as one of the major current limitations of this technique for detecting and characterizing planets, particularly at the low-mass end, one that the next Decadal Survey should consider very seriously. A number of options are presented that include buying time on existing telescopes with high velocity precision instrumentation, the deployment of instruments with 1 m/s capability on underutilized 2-4m class telescopes, and the construction of 2-8m class dedicated telescopes.

Proceedings of the International Astronomical Union, Jan 2, 2004

In the summer and fall of 2000 the yellow hypergiant Rho Cassiopeiae dimmed by more than a visual... more In the summer and fall of 2000 the yellow hypergiant Rho Cassiopeiae dimmed by more than a visual magnitude, while its effective temperature decreased from \~7000 K to below 4000 K over 200 d. We observed the highest mass-loss rate of 5 % of the solar mass per year in a single stellar eruption so far (Lobel et al. 2003, ApJ, 583, 923). We determine from newly formed TiO bands a gas mass-loss rate of M_dot 5.4 10^{-2} Msun/yr, which is of the same order of magnitude as has been proposed for the giant outbursts of the Luminous Blue Variable Eta Carinae. Over the past two years since the outburst event we observe a very prominent inverse P Cygni profile in Balmer H alpha. Strong Halpha emission has not before been observed in the hypergiant over this long period of time, signaling an unusual strong collapse of the upper hydrogen atmosphere, which we also observed in the months before the 2000 outburst. Since the brightness decrease of March 2003 we observe a transformation of the H alpha profile into a P Cygni profile, signaling a strong expansion of Rho Cas's upper atmosphere, which could possibly result in a new outburst event. High-resolution spectroscopic observations reveal that the lower photosphere rapidly expanded until May-June 2003. Very recent high-resolution observations of September 2003 show however that the photospheric absorption lines did not shift far blueward as observed in July 2000 before the strong brightness decrease of the outburst. The Fe I 5572 A is redshifted, signaling the collapse of the lower photosphere. A new strong brightness decrease by more than a magnitude in V for the fall and winter of 2003 is therefore not expected.

Noao Proposal, Aug 1, 2005

This proposal is part of a project to establish comprehensive and reliable membership information... more This proposal is part of a project to establish comprehensive and reliable membership information for four rich, old open clusters (NGC 2506, NGC 2682, NGC 6791, and NGC 7789) using accurate space motions. For each cluster we will provide highly reliable three-dimensional kinematic membership determinations for the entire evolved cluster population; excellent two-dimensional kinematic membership determinations for cluster members to masses as low as 0.5 M_⊙; and a complete census of the short-period binary population among the solar-type stars, with orbital solutions for periods up to 10^3 days. As one scientific outcome, our radial-velocity surveys will lay the foundation for studies of the dynamical evolution of cluster binary populations and for an exploration of the interplay between stellar evolution and stellar dynamics, as traced by ?anomalous? stars that cannot be explained by single-star evolutionary theory. This is a program integrating the Mayall 4-m for astrometric imaging with the WIYN 3.5m/Multi-Object Spectrograph and the MMT/Hectochelle for high- precision radial-velocities. Here we request time with MMT/Hectochelle to obtain radial velocities of faint stars in the crowded cores of the more distant clusters in our sample, NGC 2506, NGC 6791, and NGC 7789.

For many decades the determination of accurate fundamental parameters for stars (masses, radii, t... more For many decades the determination of accurate fundamental parameters for stars (masses, radii, temperatures, luminosities, etc.) has mostly been the domain of eclipsing binary systems. That has begun to change as long-baseline interferometric techniques have improved significantly, and powerful new instruments have come online. This paper will review the status of the field, and in particular how the knowledge of precise stellar properties helps us understand stars. Main-sequence stars similar to the Sun are by far the best studied, but much remains to be done for other kinds of objects such as early-type as well as late-type stars including brown dwarfs, evolved stars, metal-poor stars, and pre-main sequence stars. Progress is illustrated with several examples of how interferometry has contributed significantly in some of these areas.

We report the detection of a transiting Jupiter-sized planet orbiting a relatively bright (V=11.7... more We report the detection of a transiting Jupiter-sized planet orbiting a relatively bright (V=11.79) K0V star. We detected the transit light-curve signature in the course of the TrES multi-site transiting planet survey, and confirmed the planetary nature of the companion via multicolor photometry and precise radial velocity measurements. We designate the planet TrES-1; its inferred mass is 0.75 +/- 0.07 Jupiter masses, its radius is 1.08 (+0.18/-0.04) Jupiter radii, and its orbital period is 3.030065 +/- 0.000008 days. This planet has an orbital period similar to that of HD 209458b, but about twice as long as those of the OGLE transiting planets. Its mass is indistinguishable from that of HD 209458b, but its radius is significantly smaller and fits the theoretical models without the need for an additional source of heat deep in the atmosphere, as has been invoked by some investigators for HD 209458b.

Bulletin of the American Astronomical Society, May 1, 2003

To date, one of the fundamental questions about the origin/nature of planetary systems still rema... more To date, one of the fundamental questions about the origin/nature of planetary systems still remains unanswered: Do gas giant planets form by core accretion or disk instability? Among the two proposed mechanisms for gas giant planet formation, core accretion is likely to be enhanced in metal-rich stars, as increased surface densities of solids can shorten the overall time-scales for giant planet formation by this mechanism, while disk instability is remarkably insensitive to the primordial metallicity of the protoplanetary disk. Very few metal-poor stars have been searched for planets so far, and the implication that there may be no planets orbiting field metal-poor stars simply has not been tested yet. In fact, the absence of very close-in (P < 8.3 days) planets in the moderately metal-poor ([Fe/H] ˜ -0.7) globular cluster 47 Tuc may be due to a lack of planet formation because of the low metallicity. Alternatively, the dense stellar environment in the cluster may have interfered with planet formation, or with migration to close-in orbits, or with planet survival. By conducting a search for planets around a sample of nearby metal-poor dwarfs in the field, where the stellar density is much lower, dynamical interactions in a dense stellar environment can be eliminated as a factor, and it will be possible to unambiguously determine the role of metallicity in gas giant planet formation. Here we present preliminary results from our search for planets within 1 AU around a well-controlled sample of metal-poor stars using the Keck 1 telescope. A. S. is greatly indebted to the Smithsonian Astrophysical Observatory for support through the SAO Predoctoral Fellowship program and to the University of Pittsburgh for support through the Mellon Predoctoral Fellowship program.