Papers by Guillermo Torres
En la última década se ha hecho un esfuerzo observacional importante para determinar los parámetr... more En la última década se ha hecho un esfuerzo observacional importante para determinar los parámetros físicos de estrellas poco masivas (M < 1 Msol). Las observaciones más recientes parecen indicar una discrepancia entre la relación masa-radio que predicen los modelos y la que se obtiene de los datos observacionales. Esta discrepancia parece explicarse por la presencia de fuertes campos magnéticos en estas estrellas que inducen radios más grandes de los que predicen los modelos. Las fuentes más precisas de masas y radios estelares son las binarias eclipsantes separadas de doble línea (DDEBs por su siglas en inglés). Mediante las curvas de velocidades radiales y las curvas de luz para estos sistemas es posible obtener masas y radios con precisiones del orden de 1-2%. Sin embargo, el número de DDEBs poco masivas conocidas hasta ahora es pequeño y, en algunos casos, las incertidumbres en las masas y radios son grandes. En el año 2005 comenzamos una campaña de observación sistemática d...
The Astrophysical Journal, 2015
We present the discovery of Kepler-453 b, a 6.2 R Å planet in a low-eccentricity, 240.5 day orbit... more We present the discovery of Kepler-453 b, a 6.2 R Å planet in a low-eccentricity, 240.5 day orbit about an eclipsing binary. The binary itself consists of a 0.94 and 0.195 M ☉ pair of stars with an orbital period of 27.32 days. The plane of the planetʼs orbit is rapidly precessing, and its inclination only becomes sufficiently aligned with the primary star in the latter portion of the Kepler data. Thus three transits are present in the second half of the light curve, but none of the three conjunctions that occurred during the first half of the light curve produced observable transits. The precession period is ∼103 years, and during that cycle, transits are visible only ∼8.9% of the time. This has the important implication that for every system like Kepler-453 that we detect, there are ∼11.5 circumbinary systems that exist but are not currently exhibiting transits. The planetʼs mass is too small to noticeably perturb the binary, and consequently its mass is not measurable with these data; however, our photodynamical model places a 1σ upper limit of M 16 Å. With a period 8.8 times that of the binary, the planet is well outside the dynamical instability zone. It does, however, lie within the habitable zone of the binary, making it the third of 10 Kepler circumbinary planets to do so.
The Astronomical Journal, 2014
AP And is a well-detached F5 eclipsing binary star for which only a very limited amount of inform... more AP And is a well-detached F5 eclipsing binary star for which only a very limited amount of information was available before this publication. We have obtained very extensive measurements of the light curve (19097 differential V magnitude observations) and a radial velocity curve (83 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.277 ± 0.004 and 1.251 ± 0.004 solar masses, radii of 1.233 ± 0.006 and 1.1953 ± 0.005 solar radii, and temperatures of 6565 ± 150 K and 6495 ± 150 K. The distance to the system is about 400 ± 30 pc. Comparison with the theoretical properties of the stellar evolutionary models of the Yonsei-Yale series of Yi et al. shows good agreement between the observations and the theory at an age of about 500 Myr and a slightly sub-solar metallicity.
New Astronomy Reviews, 2014
We examine the performance of standard pre-main-sequence (PMS) stellar evolution models against t... more We examine the performance of standard pre-main-sequence (PMS) stellar evolution models against the accurately measured properties of a benchmark sample of 26 PMS stars in 13 eclipsing binary (EB) systems having masses 0.04-4.0 M ⊙ and nominal ages ≈1-20 Myr. We provide a definitive compilation of all fundamental properties for the EBs, with a careful and consistent reassessment of observational uncertainties. We also provide a definitive compilation of the various PMS model sets, including physical ingredients and limits of applicability. No set of model isochrones is able to successfully reproduce all of the measured properties of all of the EBs. In the H-R diagram, the masses inferred for the individual stars by the models are accurate to better than 10% at 1 M ⊙ , but below 1 M ⊙ they are discrepant by 50-100%. Adjusting the observed radii and temperatures using empirical relations for the effects of magnetic activity helps to resolve the discrepancies in a few cases, but fails as a general solution. We find evidence that the failure of the models to match the data is linked to the triples in the EB sample; at least half of the EBs possess tertiary companions. Excluding the triples, the models reproduce the stellar masses to better than ∼10% in the H-R diagram, down to 0.5 M ⊙ , below which the current sample is fully contaminated by tertiaries. We consider several mechanisms by which a tertiary might cause changes in the EB properties and thus corrupt the agreement with stellar model predictions. We show that the energies of the tertiary orbits are comparable to that needed to potentially explain the scatter in the EB properties through injection of heat, perhaps involving tidal interaction. It seems from the evidence at hand that this mechanism, however it operates in detail, has more influence on the surface properties of the stars than on their internal structure, as the lithium abundances are broadly in good agreement with model predictions. The EBs that are members of young clusters appear individually coeval to within 20%, but collectively show an apparent age spread of ∼50%, suggesting true age spreads in young clusters. However, this apparent spread in the EB ages may also be the result of scatter in the EB properties induced by tertiaries.
EPJ Web of Conferences, 2013
We present our search for young transiting planets at ages of 2 to 20 Myr. Towards this goal, we ... more We present our search for young transiting planets at ages of 2 to 20 Myr. Towards this goal, we monitor a number of young open clusters with the YETI network. YETI consists of 0.4-2 m-sized telescopes at different longitudes that observe continuously over timescales much longer than a night. In our first cluster Trumpler 37 we found more than 350 variable stars. Also two transiting candidates were found so far, for which follow-up is partly done. The first candidate turned out to be an eclipsing binary with an M-type companion. We describe the research done on these two transiting candidates.
We propose to observe the FUV spectrum of the hot, helium-core white dwarf in the binary system H... more We propose to observe the FUV spectrum of the hot, helium-core white dwarf in the binary system HR 1608 in order to determine if there are suitable spectral lines to obtain a radial velocity orbit for the white dwarf star. The primary star in this system, with spectral type K0 IV, dominates the spectrum at visual wavelengths. At a temperature of around 25, 000 K, however, the white dwarf outshines the primary in the UV. The orbital motion of the primary star has been monitored for seven years with the CfA Digital Speedometer at Oak Ridge Observatory in Harvard, MA. In addition, the Hipparcos team noted excess scatter in the astrometric solution which, though unexplained at the time, we now know to be due to the orbital motion. Combining the astrometric and spectroscopic data, we have solved for the orbital elements, including the inclination of the system. In order to obtain a dynamical mass for the star, the orbital motion of both stars must be observed, thus the need for monitorin...
The Astrophysical Journal, 2012
We report homogeneous spectroscopic determinations of the effective temperature, metallicity, and... more We report homogeneous spectroscopic determinations of the effective temperature, metallicity, and projected rotational velocity for the host stars of 56 transiting planets. Our analysis is based primarily on the Stellar Parameter Classification (SPC) technique. We investigate systematic errors by examining subsets of the data with two other methods that have often been used in previous studies (SME and MOOG). The SPC and SME results, both based on comparisons between synthetic spectra and actual spectra, show strong correlations between T eff , [Fe/H], and log g when solving for all three quantities simultaneously. In contrast the MOOG results, based on a more traditional curve-of-growth approach, show no such correlations. To combat the correlations and improve the accuracy of the temperatures and metallicities, we repeat the SPC analysis with a constraint on log g based on the mean stellar density that can be derived from the analysis of the transit light curves. Previous studies that have not taken advantage of this constraint have been subject to systematic errors in the stellar masses and radii of up to 20% and 10%, respectively, which can be larger than other observational uncertainties, and which also cause systematic errors in the planetary mass and radius.
The Astrophysical Journal, 2007
The bright K1 III-IV star γ Cep has been reported previously to have a companion in a ∼2.5-yr orb... more The bright K1 III-IV star γ Cep has been reported previously to have a companion in a ∼2.5-yr orbit that is possibly substellar, and also has a stellar companion at a larger separation that has never been seen. Here we determine for the first time the three-dimensional orbit of the stellar companion accounting also for the perturbation from the closer object. We combine new and existing radial velocity measurements (of both classical precision and high precision) with intermediate astrometric data from the Hipparcos mission (abscissa residuals) as well as ground-based positional observations going back more than a century. The orbit of the secondary star is eccentric (e = 0.4085 ± 0.0065) and has a period P = 66.8 ± 1.4 yr and a semimajor axis of 19.02 ± 0.64 AU. We establish the primary star to be on the first ascent of the giant branch, and to have a mass of 1.18 ± 0.11 M ⊙ , an effective temperature of 4800 ± 100 K, and an age around 6.6 Gyr (for an assumed metallicity [Fe/H] = +0.01 ± 0.05). The unseen secondary star is found to be an M4 dwarf with a mass of 0.362 ± 0.022 M ⊙ , and is expected to be ∼8.4 mag fainter than the primary in V and ∼6.4 mag fainter in K. The minimum mass of the putative planetary companion is M p sin i = 1.43 ± 0.13 M Jup , the inclination angle of its orbit being unknown. Taking advantage again of the high-precision Hipparcos observations we are able to place a dynamical upper limit on this mass of 13.3 M Jup at the 95% confidence level, and 16.9 M Jup at the 99.73% (3σ) confidence level, thus confirming that it is indeed substellar in nature. The orbit of this object (semimajor axis 1.94 ± 0.06 AU) is only 9.8 times smaller than the orbit of the secondary star (the smallest ratio among exoplanet host stars in multiple systems), but it is stable if coplanar with the binary.
The Astrophysical Journal, 2006
We present spectroscopic and photometric observations of the eclipsing system V1061 Cyg (P ¼ 2:35... more We present spectroscopic and photometric observations of the eclipsing system V1061 Cyg (P ¼ 2:35 days). A third star is visible in the spectrum, and the system is a hierarchical triple. We combine the radial velocities for the three stars, times of eclipse, and intermediate astrometric data from the Hipparcos mission (abscissa residuals) to establish the elements of the outer orbit, which is eccentric and has a period of 15.8 yr. We determine accurate values for the masses, radii, and effective temperatures of the binary components:
The Astrophysical Journal, 2014
As part of the BANANA project (Binaries Are Not Always Neatly Aligned), we have found that the ec... more As part of the BANANA project (Binaries Are Not Always Neatly Aligned), we have found that the eclipsing binary CV Velorum has misaligned rotation axes. Based on our analysis of the Rossiter-McLaughlin effect, we find sky-projected spin-orbit angles of β p = −52 ± 6 • and β s = 3 ± 7 • for the primary and secondary stars (B2.5V + B2.5V, P = 6.9 d). We combine this information with several measurements of changing projected stellar rotation speeds (v sin i) over the last 30 years, leading to a model in which the primary star's obliquity is ≈ 65 • , and its spin axis precesses around the total angular momentum vector with a period of about 140 years. The geometry of the secondary star is less clear, although a significant obliquity is also implicated by the observed time variations in the v sin i. By integrating the secular tidal evolution equations backward in time, we find that the system could have evolved from a state of even stronger misalignment similar to DI Herculis, a younger but otherwise comparable binary.
The Astrophysical Journal, 2011
The detection and characterization of the first transiting super-Earth, CoRoT-7 b, has required a... more The detection and characterization of the first transiting super-Earth, CoRoT-7 b, has required an unprecedented effort in terms of telescope time and analysis. Although the star does display a radial-velocity signal at the period of the planet, this has been difficult to disentangle from the intrinsic stellar variability and pinning down the velocity amplitude has been very challenging. As a result, the precise value of the mass of the planet-and even the extent to which it can be considered to be confirmed-has been debated in the recent literature, with six mass measurements published so far based on the same spectroscopic observations, ranging from about 2 to 8 Earth masses. Here we report on an independent validation of the planet discovery using one of the fundamental properties of a transit signal: its achromaticity. We observed four transits of CoRoT-7 b at 4.5 μm and 8.0 μm with the Infrared Array Camera (IRAC) on board the Spitzer Space Telescope in order to determine whether the depth of the transit signal in the near-infrared is consistent with that observed in the CoRoT bandpass, as expected for a planet. We detected the transit and found an average depth of 0.426 ± 0.115 mmag at 4.5 μm, which is in good agreement with the depth of 0.350 ± 0.011 mmag (ignoring limb darkening) found by CoRoT. The observations at 8.0 μm did not yield a significant detection. The 4.5 μm observations place important constraints on the kinds of astrophysical false positives that could mimic the signal. Combining this with additional constraints reported earlier, we performed an exhaustive exploration of possible blend scenarios for CoRoT-7 b using the BLENDER technique. We are able to rule out the vast majority of false positives, and the remaining ones are found to be much less likely than a true transiting planet. We thus validate CoRoT-7 b as a bona fide planet with a very high degree of confidence, independently of any radial-velocity information. Our Spitzer observations have additionally allowed us to significantly improve the ephemeris of the planet, so that future transits should be recoverable well into the next decade. In its warm phase Spitzer is expected to be an essential tool for the validation, along the lines of the present analysis, of transiting planet candidates with shallow signals from CoRoT as well as from the Kepler mission, including potentially rocky planets in the habitable zones of their parent stars.
The Astrophysical Journal, 2005
We report on Keck Interferometer observations of the double-lined binary (B) component of the qua... more We report on Keck Interferometer observations of the double-lined binary (B) component of the quadruple pre-main sequence (PMS) system HD 98800. With these interferometric observations combined with astrometric measurements made by the Hubble Space Telescope Fine Guidance Sensors (FGS), and published radial velocity observations we have estimated preliminary visual and physical orbits of the HD 98800 B subsystem. Our orbit model calls for an inclination of 66.8 ± 3.2 deg, and allows us to infer the masses and luminosities of the individual components. In particular we find component masses of 0.699 ± 0.064 and 0.582 ± 0.051 M ⊙ for the Ba (primary) and Bb (secondary) components respectively. Spectral energy distribution (SED) modeling of the B subsystem suggests that the B circumstellar material is a source of extinction along the line of sight to the B components. This seems to corroborate a conjecture by Tokovinin that the B subsystem is viewed through circumbinary material, but it raises important questions about the morphology of that circumbinary material.
The Astronomical Journal, 2013
New photometric, spectroscopic, and eclipse timing observations of the eclipsing binary star HP A... more New photometric, spectroscopic, and eclipse timing observations of the eclipsing binary star HP Aur allow for very accurate orbital determinations, even in the presence of a third body and transient starspot activity. The eclipsing binary masses are determined to an accuracy of ±0.4% and the radii to ±0.6%. The masses are 0.9543 ± 0.0041 and 0.8094 ± 0.0036 solar masses, and the radii are 1.0278 ± 0.0042 and 0.7758 ± 0.0034 solar radii, respectively. The orbital period in the outer orbit is accurately known for the first time: 4.332 ± 0.011 years. A comparison with current theories of stellar evolution show that the components' absolute properties can be well-matched by the current models at an age of about 7 billion years.
The Astronomical Journal, 1999
We present new measurements of the relative positions of the components of the low-mass visual bi... more We present new measurements of the relative positions of the components of the low-mass visual binary Wolf 424 (M5.5 Ve) made with the Fine Guidance Sensors on the Hubble Space T elescope. Previous analyses of the astrometric orbit of this system indicated that the components have substellar masses (Heintz ; Schultz et al.), raising considerable interest as the Ðrst candidate brown dwarfs to have their masses measured dynamically. These studies relied partly on visual and photographic measurements, which are a †ected by systematic errors in the angular separation and have thus biased those solutions. Our new orbital solution using only the position angles of the early measurements together with all available modern high-resolution observations including our own shows that the component masses are clearly above the substellar limit and (M A \ 0.143^0.011 M _ , M B \ 0.131^0.010 M _), thus they are not brown dwarfs. Recent evolutionary models for low-mass stars show good agreement with the location of Wolf 424A and B in the mass-luminosity diagram in the K band. In addition, we show that while the secondary appears to have normal colors compared to similar M dwarfs, the primary star is fainter than expected at optical wavelengths (B, V), possibly owing to signiÐcant spot coverage. This is consistent with the strong Ñaring activity displayed by the system.
The Astronomical Journal, 2008
We present new V-band differential photometry and radial-velocity measurements of the unevolved 1... more We present new V-band differential photometry and radial-velocity measurements of the unevolved 1.18-day period F+G-type double-lined eclipsing binary VZ Cep. We determine accurate values for the absolute masses, radii, and effective temperatures as follows: M A = 1.402 ± 0.015 M ⊙ , R A = 1.534 ± 0.012 R ⊙ , T eff = 6690±160 K for the primary, and M B = 1.1077±0.0083 M ⊙ , R B = 1.042±0.039 R ⊙ , T eff = 5720 ± 120 K for the secondary. A comparison with current stellar evolution models suggests an age of 1.4 Gyr for a metallicity near solar. The temperature difference between the stars, which is much better determined than the absolute values, is found to be ∼250 K larger than predicted by theory. If all of this discrepancy is attributed to the secondary (which would then be too cool compared to models), the effect would be consistent with similar differences found for other lowmass stars, generally believed to be associated with chromospheric activity. However, the radius of VZ Cep B (which unlike the primary, still has a thin convective envelope) appears normal, whereas in other stars affected by activity the radius is systematically larger than predicted. Thus, VZ Cep poses a challenge not only to standard theory but to our understanding of the discrepancies in other low-mass systems as well.
The Astronomical Journal, 1992
... Bowling Green, Ohio 43403 GUILLERMO TORRES Harvard-Smithsonian Center for Astrophysics, 60 Ga... more ... Bowling Green, Ohio 43403 GUILLERMO TORRES Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 and Córdoba Observatory, National University of Córdoba, Laprida 854, 5000 Córdoba, Argentina JON A. MORSE ...
Science, 2013
Two Small Habitable Planets NASA's Kepler space telescope was launched in 2009 with the goal ... more Two Small Habitable Planets NASA's Kepler space telescope was launched in 2009 with the goal of detecting planets the size of Earth in the habitable zone of Sun-like stars and determining the frequency of these planets. Using data from Kepler, Borucki et al. (p. 587 , published online 18 April) report the detection of a five-planet system where all the planets are smaller than twice the size of Earth and where the two outermost planets orbit in the habitable zone of their star, defined as the region where a rocky planet can host liquid water on its solid surface. The star, Kepler-62, is smaller and cooler than the Sun.
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Papers by Guillermo Torres