Gabriela Mallen-Ornelas

A Unique Solution of Planet and Star Parameters from an Extrasolar Planet Transit Light Curve

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 Rp. 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).

Emission-line abundances of absorption-selected galaxies at z < 0.5

We have obtained optical spectra of four galaxies associated with Mg II quasi-stellar object (QSO) absorbers at redshifts 0.10 < z < 0.45. We calculate the gas-phase oxygen abundance of these galaxies using the empirical R 23 strong-line method. The absolute B-band magnitudes of the galaxies span -20.6 < M B < -18.3. Ifthe metallicities lie on the R 23 upper branch (8.4 < log (O/H) + 12 < 8.9), then the metallicities of these absorption-selected galaxies span the range between 0.5 and 1.4 Z○. and would be consistent with the well-known luminosity-metallicity relation for 0.10 < z < 0.45 emission-line galaxies. However, such metallicities would be 0.5-1.0 dex higher than those observed in damped Lyman a systems (DLAs) via absorption-line measurements at similar redshifts. Conversely, the lower R 23 branch calibration yields metallicities Z ∼ 1 /7 Z○., consistent with the DLA absorption metallicities at low redshifts. In this case, the absorption-selected galaxies would lie significantly lower than the luminosity-metallicity relation for emission-line galaxies at z < 0.5. We discuss the implications and possible solutions for each scenario.

The Absorption and Emission Kinematics in the z = 0.7450 Mg II Absorber toward Q1331+17*

We present a comparative analysis of the galaxy emission and quasar (QSO) absorption kinematics of a zabs ~ 0.7450 Mg II system and its candidate absorbing galaxy (G5) located 386 (28.3 h 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] λ3727 doublet at a systemic redshift of zsys = 0.7450. From slit spectroscopy of this galaxy, we find vrot 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 λobs = 5674 A, 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, Δv ~ 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).

Searching for Planetary Transits in Galactic Open Clusters: EXPLORE/OC

Open clusters potentially provide an ideal environment for the search for transiting extrasolar planets, since they feature a relatively large number of stars of the same known age and metallicity at the same distance. With this motivation, over a dozen open clusters are now being monitored by four different groups. We review the motivations and challenges for open cluster transit surveys for short-period giant planets. Our photometric monitoring survey of Galactic southern open clusters, the Extrasolar Planet Occultation Research/ Open Clusters (EXPLORE/OC) project, was designed with the goals of maximizing the chance of finding and characterizing planets and of providing a statistically valuable astrophysical result in the case of no detections. We use the EXPLORE/OC data from two open clusters, NGC 2660 and NGC 6208, to illustrate some of the largely unrecognized issues facing open cluster surveys, including severe contamination by Galactic field stars (180%) and the relatively low number of cluster members for which high-precision photometry can be obtained. We discuss how a careful selection of open cluster targets under a wide range of criteria such as cluster richness, observability, distance, and age can meet the challenges, maximizing chances to detect planet transits. In addition, we present the EXPLORE/OC observing strategy to optimize planet detection, which includes high-cadence observing and continuously observing individual clusters rather than alternating between targets.

Properties of Extremely Red Objects in an Overdense Region

We use a serendipitously discovered overdensity of extremely red objects (EROs) to study the morphologies and cumulative surface number density of EROs in a dense environment. Our extremely deep imaging allows us to select very faint EROs, reaching KS = 21, or ~2 mag fainter than the L* of passively evolving ellipticals at z = 1.5. We find that the shape of the ERO cumulative surface number density in our overdense field mimics that of the field ERO population over all magnitudes down to KS = 21 but with a factor of 3-4 higher normalization. The excellent seeing in our images (04 in KS and 06 in R) allows for morphological classification of the brighter (KS < 19) EROs, and we find a mix of morphologies including interacting systems and disks; the fraction of pure bulges (at most 38%), galaxies with disks (at least 46%), and interacting systems (at least 21%) is consistent with morphological fractions in field ERO studies. The similarity in the shape of the cumulative surface density and morphological mix between our overdense field and the field ERO population suggests that ERO galaxies in overdense regions at z ~ 1-2 may not have had an appreciably different history from those in the field.

REDSHIFTS IN THE HUBBLE DEEP FIELD SOUTH

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 I814(AB) = 24 and obtained redshifts for 76% of them. Targets in our HDF-S sample were preselected 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 δz = 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.

The EXPLORE project: a deep search for transiting extrasolar planets

Searching for transits provides a very promising technique for finding close-in extra-solar planets. Transiting planets present the advantage of allowing one to determine physical properties such as mass and radius unambiguously. The EXPLORE (EXtra-solar PLanet Occultation REsearch) project is a transit search project carried out using wide-field CCD imaging cameras on 4-m class telescopes, and 8--10m class telescopes for velocity verifications of the photometric candidates. We describe some of the considerations that go into the design of the EXPLORE transit search to maximize the discovery rate and minimize contaminating objects that mimic transiting planets. We show that high precision photometry (2 to 10 millimag) and high time sampling (few minutes) are crucial for sifting out contaminating signatures, such as grazing binaries. We have an efficient data reduction pipeline which allows us to completely reduce the data in less than one month after the imaging observations, allowing us to conduct same-semester velocity follow-up observations, reducing the phase uncertainty. We have completed two searches using the 8k MOSAIC camera at the CTIO4m and the CFH12k camera at CFHT, with runs covering 11 and 16 nights, respectively. Using the 4400 images from the two fields, we obtained light curves for approximately 47,000 stars with better than

Kinematics of Optical Outflows in the Orion Nebula. I. The Giant Outflow HH 400 and the Irradiated Jet HH 502

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The Distance to the Draco Intermediate-Velocity Cloud

\% photometric precision. A number of light curves with flat-bottomed eclipses consistent with being produced by transiting planets has been discovered. Preliminary results from follow-up spectroscopic observations using the VLT UVES spectrograph and the Keck HIRES spectrograph obtained for a number of the candidates are presented. Data from four of these can be interpreted consistently as possible planet candidates, although further data are still required for definitive confirmations.