Browsing by Author "Mallén-Ornelas, G"

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    A unique solution of planet and star parameters from an extrasolar planet transit light curve
    (2003) Seager, S; Mallén-Ornelas, G
    There is a unique solution of the planet and star parameters from a planet transit light curve with two or more transits if the planet has a circular orbit and the light curve is observed in a bandpass where limb darkening is negligible. The existence of this unique solution is very useful for current planet transit surveys for several reasons. First, there is an analytic solution that allows a quick parameter estimate, in particular of R-p. Second, the stellar density can be uniquely derived from the transit light curve alone. The stellar density can then be used to immediately rule out a giant star ( and hence a much larger than planetary companion) and can also be used to put an upper limit on the stellar and planet radius even considering slightly evolved stars. Third, the presence of an additional fully blended star that contaminates an eclipsing system to mimic a planet transit can be largely ruled out from the transit light curve given a spectral type for the central star. Fourth, the period can be estimated from a single-transit light curve and a measured spectral type. All of these applications can be used to select the best planet transit candidates for mass determination by radial velocity follow-up. To use these applications in practice, the photometric precision and time sampling of the light curve must be high (better than 0.005 mag precision and 5 minute time sampling for a two-transit light curve).
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    Kinematics of optical outflows in the Orion Nebula.: I.: The giant outflow HH 400 and the irradiated jet HH 502
    (2001) Bally, J; Johnstone, D; Joncas, G; Reipurth, B; Mallén-Ornelas, G
    We present narrowband filter and high-resolution, velocity-resolved Fabry-Perot images of outflows in the southern portion of the Orion Nebula. HH 400 is a giant, low-velocity, redshifted bow shock located about 10' south of the core of the Orion Nebula. Its axis of symmetry passes close to the Trapezium cluster 1.5 pc to the north. The most likely point of origin is a young stellar object in the OMC-1 cloud core. HH 400 may be the remnant of a parsec-scale bipolar outflow powered by one of the young stars forming within this region. The radial velocity of gas in the limb-brightened rim of HH 400 is low, with redshifted speeds ranging from 8 to 20 km s(-1) with respect to the emission from the Orion Nebula. The shape of the bow indicates that it lies close to the plane of the sky. For an inclination angle of 30 degrees to the plane of the sky and assuming that the plasma is flowing mostly along the axis of symmetry, the visible gas at the rim of HH 400 has a mean velocity of about 30 km s(-1), a mass of about 3x10(-2) and a M-circle dot, dynamical age of about 5x10(4) yr, assuming the source lies in the OMC-1 cloud core. The estimated mass flux in the HH 400 bow is about 10(-6) M-circle dot yr(-1). The bent bipolar irradiated jet HH 502 is superposed on the western rim of HH 400. We resolve the spatial and velocity structure of the jet and its multiple bow shocks. The jet consists of a chain of photoionized segments separated by wide gaps; bow shocks lie at the leading edges of these jet segments. The mean radial velocities of the jet segments decrease with increasing distance from the source. The large radial velocity dispersions of the gas at the tips of the HH 502 internal working surfaces and the small spreading angles of the HH 502 jet segments, combined with their low radial velocities, indicate that this flow lies close to the plane of the sky. Assuming that the jet is fully ionized, that it spreads at the Mach angle, and that the internal sound speed in the photoionized gas is about 10 km s(-1), the jet must have a space velocity of about 400 km s(-1). Finally, we present velocity-resolved images of the bow shocks in HH 540, a flow that may originate from the large protoplanetary disk 181-826. Several additional high-velocity features identified in the Fabry-Perot data trace additional jets and outflows in this portion of the Orion Nebula.
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    Redshifts in the Hubble Deep Field South
    (2003) Sawicki, M; Mallén-Ornelas, G
    We present a catalog of 97 spectroscopic redshifts of z < 1 galaxies in the Hubble Deep Field South (HDF-S) and its flanking fields (FFs). In the HDF-S proper we observed approximately half the galaxies brighter than I-814(AB) = 24 and obtained redshifts for 76% of them. Targets in our HDF-S sample were pre-selected to be at z < 1 based on photometric redshifts, while in the FFs a simple magnitude cut was used. The photometric redshift preselection in the HDF-S resulted in a spectroscopic success rate that is significantly higher than in the FFs, where no preselection was applied. The rms precision of our redshift measurements, determined from repeat observations, is deltaz = 0.0003. We present the photometry and redshifts for the 97 objects for which we secured spectroscopic redshifts and describe the basic properties of this sample.
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    The absorption and emission kinematics in the z=0.7450 MgII absorber toward Q1331+17
    (2003) Ellison, SL; Mallén-Ornelas, G; Sawicki, M
    We present a comparative analysis of the galaxy emission and quasar (QSO) absorption kinematics of a z(abs) similar to 0.7450 Mg II system and its candidate absorbing galaxy (G5) located 3."86 (28.3 h(70)(-1) kpc) from the QSO. We have obtained a spectrum of the galaxy candidate, previously identified as a luminous edge-on disk, and detect the [O II] lambda3727 doublet at a systemic redshift of z(sys) = 0.7450. From slit spectroscopy of this galaxy, we find v(rot) greater than or similar to 210 km s(-1), possibly as large as 350 km s(-1). Plotted on the same velocity scale, the systemic redshift of the galaxy coincides with the center of the absorption system, although the absorption components span more than 100 km s(-1) in either direction. However, once the sense of the rotation is taken into account, there is no absorbing gas at the projected velocity of the disk rotation curve. This implies incompatibility with a simple disk scenario. Moreover, a reanalysis of archival Hubble Space Telescope (HST) data reveals that the galaxy is only 0.3L(*), considerably less luminous than previously reported in the literature. This is incompatible with the established Tully-Fisher relation at this redshift, unless approximately 2 mag of total extinction is invoked. Careful inspection of the archival HST data reveals that G5 may well be composed of two galaxies, although the quality of the data does not permit a detailed investigation of this. This possibility is further supported by the identification of a second faint emission line at lambda(obs) = 5674 Angstrom, whose distinct spatial and velocity profiles indicate that it arises in a different galaxy at a different redshift. Analysis of the absorption lines shows evidence for superbubbles in the interstellar medium of the absorbing galaxy, based on the striking symmetry between components and large Mg I/Mg II and Mg I/Fe II ratios, indicative of large densities. The large velocity separations between line pairings, Deltav similar to 150 km s(-1), indicate that these bubbles may be powered by OB associations comparable to the largest observed at z = 0 and that the gas is probably enriched to at least 1/10 solar metallicity. This is consistent with observations at low redshift that extended Mg II halos are often seen in galaxies that contain disturbed gas. Superbubbles may also explain why the absorber has a relatively large Mg II equivalent width relative to the luminosity of the associated galaxy ( or galaxies).
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    The EXPLORE project.: I.: A deep search for transiting extrasolar planets
    (2003) Mallén-Ornelas, G; Seager, S; Yee, HKC; Minniti, D; Gladders, MD; Mallén-Fullerton, GM; Brown, TM
    Planet transit searches promise to be the next breakthrough for extrasolar planet detection and will bring the characterization of short-period planets into a new era. Every transiting planet discovered will have a measured radius, which will provide constraints on planet composition, evolution, and migration history. Together with radial velocity measurements, the absolute mass of every transiting planet will be determined. In this paper we discuss the design considerations of the Extrasolar Planet Occultation Research (EXPLORE) project, a series of transiting planet searches using 4 m class telescopes to continuously monitor a single field of stars in the Galactic plane in each similar to2 week observing campaign. We discuss the general factors that determine the efficiency and the number of planets found by a transit search, including time sampling strategy and field selection. The primary goal is to select the most promising planet candidates for radial velocity follow-up observations. We show that with very high photometric precision light curves that have frequent time sampling and at least two detected transits, it is possible to uniquely solve for the main parameters of the eclipsing system (including planet radius), based on several important assumptions about the central star. Together with a measured spectral type for the star, this unique solution for orbital parameters provides a powerful method for ruling out most contaminants to transiting planet candidates. For the EXPLORE project, radial velocity follow-up observations for companion mass determination of the best candidates are done on 8 m class telescopes within 2 or 3 months of the photometric campaigns. This same-season follow-up is made possible by the use of efficient pipelines to produce high-quality light curves within weeks of the observations. We conclude by presenting early results from our first search, EXPLORE I, in which we reached better than 1% rms photometric precision (measured over a full night) on similar to37,000 stars with 14.5less than or equal toIless than or equal to18.2.