Throughout my short research career, I seem to have to desire to observe
our Universe at smaller and smaller distances beginning with quasars,
traveling past the Galactic center and ending with the search for planets
and life in our own back yard. My Galactic Center research translated
nicely to the jump to exoplanets since both rely on high contrast imaging,
and astrometry.
I am presently working in the exciting new field of molecular spectrocopy of
transiting extrasolar planetary atmospheres with Dr. Mark Swain at JPL.
As a research scientist at JPL, I am involved in the very new and exciting field of studying the atmospheres of transiting planets using HST, Spitzer and ground based observatories. This field has quickly moved past the molecular detection phase and, thanks to the nature of the observations, is resulting in a better understanding of abundance gradients, thermo-chemistry, energy trasport, photochemistry, vertical pressure profiles and many other properties of both the day side and terminator region of transiting hot Jupiter atmospheres. My contribution to the field has thus far involved improving our high contrast spectral extraction proceedures which are necessary to confidently produce a spectrum of the planetary atmosphere from the glare of the host star. I am interested in applying our methods to ground based obervation at both near- and (hopefully) mid-infrared wavelengths. Mid-infrared observations from the ground are highly problematic but essential given the loss of the IRS instrument on Spitzer. The next few years will have many more results in this field due to improved techniques and more potential targets. My eventual goal is the detection of the atmosphere of a terrestrial planet most likely orbiting an M dwarf.
For these projects, I completed two high contrast imaging programs at the Palomar 200 inch telescope with the PALAO/PHARO adaptive optics (AO) systems and infrared coronagraph to look for brown dwarf companions to nearby (<30 pc) FGKM stars and planetary companions to stars in Taurus and the Pleiades. The difference in the type of object detected is because planets are brighter when born and cool off and dim when they age. The upgraded Palomar AO system has demonstrated the ability to reach contrast levels of K~4-6 mag and 9-10 mag at separations of one and five arcseconds, respectively with a 60 sec exposure (Tanner et al. 2006 submitted; Metchev et al. 2003; Oppenheimer et al. 2000). As our observing techniques improve, we have been able to push to lower mass ratios and smaller separations. The FGKM survey has found three confirmed proper motion companions and five targets which still need 2nd epoch observations to confirm companionship (Tanner et al. 2008). Figure 2 shows an PSF subtracted image of GL 454. This star has a confirmed companion and mere 1" (13 AU) away. Given the known distance to the primary star and the brightness of the companion, this companion along with the others are post probably M dwarfs. In the Taurus/Pleiades sample, we detected 8 potential companions around 5 stars (36%) in the Pleiades and 27 potential companions around 13 stars (80%) in Taurus (Tanner et al. 2007). The star with the closest companion, BP Tau, has a star with a 3.1" (~400 AU) projected separation. If this star were a true companion then it would have a mass of ~ 5 MJ according to the atmospheric models of Burrows et al (1997, 2003) and assuming a distance of 140 pc. This separation seems large for a planetary companion although one of the putative directly imaged planets, AB Pic, has a projected separation of 275 AU (Chauvin et al. 2005) and some theories predict that giant planets could reside at large distances if they underwent an outward migration as a result of a gravitational interaction with an inner planet (Boss 2006).
The distance to the Taurus and Pleiades clusters has made proper motion confirmation much more problematic compared to the nearby FGKM sample. Despite careful pixel scale and image orientation calibration, the target stars have not moved enough over the two year baseline between epochs to definitively conclude whether the companions share their proper motion. To improve the astrometric accuracies of existing AO+coronagraph systems, I would like to develop a device similar to that described by Sivaramakrishnan & Oppenheimer (2006). The device is a wire grid placed in the pupil plane resulting in a fiducial image of the target star at a known distance and flux from the star's true position. Each science image with have both an astrometric and a flux calibrator within the image thus removing the need to take additional images with the spot offset from the target. This will be especially useful in detecting faint companions to the young stars since the longer exposures used to achieve the required S/N on the target star result in PSF smearing.
I have developed a set of Monte Carlo simulations that determine the number of terrestrial mass planets we can expect to detect and characterize during a SIM PlanetQuest five year mission given its known instrumental errors and the intrinsic properties of the planets and host stars. My collaborator who focused on the detection of the planets with a joint periodogram, recently published a paper summarizing SIM's ability to find terrestrial mass planet in the habitable zones of nearby stars (Catanazarite et al. 2006). I have just submitted the follow-up paper which addresses SIM's ability to measure the orbits of those planets it detects (Tanner et al. in prep). Getting the unambiguous masses of the planets will obviously tell us a great deal about the population of terrestrial mass planets. Also estimating the orbital phase of the planet will be a great benefit to future TPF-like missions since this will tell the observers when the planet is at its widest separation from the star and, thus, whether and when it is beyond the inner working angle of the coronagraph or nuller. As part of this study, I have been collaborating with SIM scientists over the assessment of the best targets for the EPIcS planet search program. We are considering both the astrophysical properties of the stars and the instrumental requirements of SIM when ranking the best potential targets for detecting terrestrial mass planets in the habitable zone of these planets. This is an on-going process which will provide updated target lists for the many precursor programs being conducted for the project including imaging and radial velocity surveys. In addition, this information will be useful in determining which of the stars are also good targets for the Terrestrial Planet Finder or missions like it.
I am involved in number of Spitzer studies of nearby FGK stars with both MIPS and IRS. These projects include a survey of FGK stars with IRS (Beichman et al. 2006, Lawler et al. 2008, Beichman et al. 2008 in prep), a detailed study of those FGK stars resolved at 70 micron (Bryden et al. 2008) and a sub-sample of the FGK stars at 160 microns (Tanner et al. 2008). One of the stars, HD 69830, not only has a distinctive debris disk (Beichman et al. 2006), it also has a newly discovered set of radial velocity planets (Lovis et al 2006). These Spitzer programs have not only probed the frequency of debris disks around nearby stars but are also determining their physical properties so that we can compare them to the properties of any planetary systems further exploring the planet disk connection. I am presently finishing up a Northern high contrast imaging survey of stars with Spitzer excesses with the Palomar AO system. The goal of this program is to study the affect of stellar and brown dwarf companions on solar system formation.
Graduate Research Assistant - Dr. Andrea GhezMy PhD thesis is centered around a collection of enigmatic mid-infrared sources located within the central parsec of the Galactic Center. These objects have large near-infrared (near-IR) polarization, extremely cool colors, and featureless near-IR spectra. My goal is to identify the nature of these sources and provide an explanation for their existence given the dynamic environment of the Galactic Center - home of the supermassive black hole, SgrA*. I have assembled three types of observations of the Northern Arm and Quintuplet sources: near- and mid-IR sizes, photometry and spectra using data from the 10-meter Keck telescopes as well as public near-infrared AO images from the 8-meter Gemini North telescope. The main focus of my research has been the source, IRS 21, which lies a mere 4 arcseconds from Sgr A*. As a result, I have published a paper on its well constrained resolved near- and mid-infrared sizes and SED properties which suggest IRS 21 is surrounded by a 1000 AU, geometrically thin dust shell - much too large to be intrinsically associated with its central heating source (Tanner et al. 2002).
The Gemini AO images show clear signs of a bow shock around IRS 8. This observation and the large intrinsic size lead to the hypothesis that the extended nature of IRS 21 is also due to a bowshock. Clear asymmetric structure can be seen around IRS 1W, 10W, 5 and 2 in both the raw near-infrared speckle images and in images carefully deconvolved using both Lucy-Richardson and IDAC (Blind) algorithms. The morphology of all of the sources except IRS 10W resemble the horse-shoe shape seen around IRS 8 but on a smaller spatial scale. Comparisons of the proper motions of some of the NA sources with the motion of the Northern Arm diffuse material, provided by orbital models taken from the literature, result in a consistent picture in which the observed extended structure are bowshocks created by the interaction of the diffuse material with the strong stellar winds of the central star most likely a massive early-type star or its more evolved counterpart - a Wolf-Rayet (WC9) star. While we still do not observe photospheric lines from the central source, thus providing a spectral type, our ability to say these are most probably windy, massive stars like those observed in the nearby IRS 16 cluster adds five more (IRS 8, 5, 1W, 21 and 2) to the 16 such stars previously identified in the region through their HeI emission lines (Tanner et al. 2002, in prep).
However, the sample criteria for my thesis is a large K-L color (>3) rather than being spatially resolved at 2.2 microns. This criteria also includes the sources, IRS 3, 29N and 6Ewithin the central parsec and the "Quintuplet proper members" in the nearby Quintuplet cluster 30 arcseconds away. IRS 3, 29N and 6E show no sign of being resolved in our near-IR speckle observations while two of the Quintuplet sources do show a small amount of extended emission. IRS 3 is noticeably extended in our MIRLIN mid-infrared images while the LWS mid-infrared observations of the Quintuplet sources provide only upper limits of ~8,000 AU due to poor seeing conditions. Since none of these sources are coincident with the amount of diffuse emission associated with the Northern Arm, their red colors and extended structure are likely due to intrinsic dust photospheres.
Finally, this research has been one of the many projects to result from our near- and mid-infrared observations of the central parsec which include the study of the proper motions of the sources around Sgr A* (Ghez et al. 2000), near- and mid-infrared limits on the emission from Sgr A* (Hornstein et al. 2002, Morris et al. 2002 in prep), and mid-infrared morphology and temperature structure of the central parsec (Cotera et al. 2002 in prep). I have been involved in all these projects in some form or fashion. I plan on continuing observations of the Northern Arm sources using the latest in near-infrared adaptive optics imaging and spectroscopy (laser guide stars, NIR wavefront sensors, etc.)
As a researcher at NOAO, I studied quasar Lyman alpha systems observed by the HST Quasar Absorption Line Key Project. The purpose of the project is to correlate the absorption lines seen with HST to the spatial distribution of galaxies. I reduced CCD images from the KPNO Burrell-Schmidt telescope. I then used the FOCAS program to select galaxies in the image for redshift measurements using the HYDRA spectroscope on the WIYN telescope and the Cryocam spectroscope on the KPNO 4 meter telescope. Finally, I created a reference table and organized the data which will be used to continue the project.
160 micron Survey for Debris Disks with Spitzer, Tanner, A., Beichman, C., Bryden, G., Lawler, S., et al. 2008, submitted
Palomar AO+Chronograph Companion Search Around EPIcS SIM Planetquest Targets, Tanner, A., Gelino, C., Shao, M., 2008, in prep
Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest, Unwin, S., Shao, M., Tanner, A., et al. 2008, PASP, 863, 38
SIM PlanetQuest Key Project Precursor Observations to Detect Gas Giant Planets Around Young Stars, Tanner, A., Beichman, C., 2007, ApJ,119, 747
Pinwheels in the Quintuplet Cluster, Tuthill, P., Monnier, J., Tanner, A., et al. 2006, Science, vol 313, p 935
IRS Spectra of Solar-Type Stars: A Search for Astroid Belt Analogs, Beichman, C., Tanner, A., ApJ, 2006, 639, 1166
Astrometric Detection of Terrestrial Planets in the Habitable Zones of Nearby Stars with SIM PlanetQuest, Catanzarite, J., Shao, M., Tanner, A., Unwin, S., & Yu, J. 2006, PASP, 118, 1322
High Spectral Resolution Observations of the Massive Stars in the Galactic Center A. M. Tanner, D. Figer, et al. 2006, ApJ, 641, 891
Stellar Bowshocks in the Northern Arm of the Galactic Center: More Members and Kinematics of the Massive Star Population A. M. Tanner, A. Ghez, M. Morris, J. C. Christou, ApJ, 2005, 624, 742
"Newly Resolved Bow Shocks within the Central Parsec", Tanner, A.,M., Ghez, A., Morris, M., Becklin, E., 2003, Astron. Nachr., Vol., 324, 597
"Journey to the Galactic Center", Tanner, A., 2003, Sky and Telescope, April issue
"Spatially Resolved Observations of the Galactic Center Source, IRS 21", Tanner, A.,M., Ghez, A., Morris, M., Becklin, E., Cotera, A., Ressler, M., Werner, M., Wizinowich, P. 2002, ApJ, 575, 860
"Near-Infrared Variability of Sgr A*", Hornstein, S., Ghez, A., Tanner, A., Morris, M., Becklin, E., 2002, ApJ, 577, L9
"The First Measurement of Spectral Lines in a Short-Period Star Bound to the Galaxy's Central Black Hole: A Paradox of Youth", Ghez, A. M., Duchene, G., Matthews, K., Hornstein, S., Tanner, A., et al. 2003, ApJL, in press
"Mid-Infrared Images of the Central Parsec", Cotera, A., Tanner, A., Morris, M., Ghez, A., Becklin, E., Ressler, M., in prep
"Mid-Infrared Limits on Emission from Sagittarius A*", Morris, M.,Tanner, A.,, Ghez, A., Becklin, E., Cotera, A., Ressler, M., in prep
"The Accelerations of Stars orbiting the Milky Way's Central Black Hole" , Ghez, A,M, Morris, M, Becklin, E,E, Tanner, A, Kremenek, T, 2000, Nature, 407, 349
"Is the Galactic Center Source, IRS 21, as Large as It Appears?", A.M. Tanner, A.M. Ghez, M. Morris, E.E. Becklin, A. Cotera, M., Ressler, 2000, SPIE Conf. Proceeding, 4005, 180
"Spatially Resolved Dust Shells in the Central Parsec" , Tanner, A., Ghez, A.M., Morris, M., in The Central Parsecs, Galactic Center Workshop 1998, Tucson, . 7-11, 1998, Eds. H. Falcke, A. Cotera, W. Huschl, F. Melia, and M. Rieke;
"Towards Complete Stellar Orbits around the Galaxy's Central Black Hole: The First Acceleration Measurements" , A. M. Ghez, T. Kremenek, A. Tanner, M. Morris, and E. Becklin, 1998, ESO Proceedings of "Black Holes in Binaries and Galactic Nuclei"
"Mid-Infrared Imaging of the Central Parsec with Keck", Cotera, A.; Morris, M.; Ghez, A. M.; Becklin, E. E.; Tanner, A. M.; Werner, M. W.; Stolovy, S. R.in The Central Parsecs, Galactic Center Workshop 1998, Tucson, Sep. 7-11, 1998, Eds. H. Falcke, A. Cotera, W. Huschl, F. Melia, and M. Rieke; the ASP Conf. Ser.
"The Study of Quasar Absorption Line Systems with IRAS" Tanner, A. M., Bechtold, J., Cutri, R.M., Walker, C.E., Black, J., 1996, AJ, 112, 62
"Space Interferometry Mission (SIM) PlanetQuest's Discovery Space and Potential Synergy with Terrestrial Planet Finder (TPF): I. Detection of Terrestrial Planets in the Habitable Zone" , Catanzarite, J., Tanner, A., Shao, M. May 2005, BAAS, 206, 14.04
"Space Interferometry Mission (SIM) PlanetQuest's Discovery Space and Potential Synergy with the Terrestrial Planet Finder (TPF): II. Orbit and Mass Characterization of Terrestrial Planets in the Habitable Zone" , Tanner, A., Catanzarite, J., Shao, M. May 2005, BAAS, 206, 14.05
"An Astrometric Search for Jupiters Around Young Stars with SIM-PlanetQuest" , Beichman, C., Tanner, A., Mohanty, S., YSO SIM Team, May 2005, BAAS, 206, 09.06
"Resolving the Enigmatic Northern Arm Sources in the Central Parsec" , A.M. Tanner, Jan 2003, BAAS, 201, 31.04
"Full 3-D Orbital Solutions for Stars Making a Close Approach to the Supermassive Black Hole at the Center of the Galaxy" Ghez, A. et al., Jan 2003, BAAS, 201, 68.04
"MIR Imaging of the Galactic Center: Dust Temperature and Opacity in the Central Parsec" , A. Cotera, A.M. Tanner, M.Morris, A.M. Ghez, E.E. Becklin, M.W. Werner, Jan. 2002, BAAS, 85.06
"AO Study of the Galactic Center Using the Keck Telescopes", S. Hornstein, A. Ghez, S. Gezari, A. Tanner, D. Sands, 2001, CfAO Retreat, Monterey, CA, December 8-10.
"Mid-Infrared Limits on Emission from Sagittarius A*", M. Morris, A.M. Tanner, A.M. Ghez, E.E. Becklin, A. Cotera, M.W. Werner, M.E. Ressler, June, 2001, BAAS, 41.01
"Journey to the Center of the Galaxy", A. M. Tanner, 2001, Integrating Research and Education, CfAO Workshop, Kona, HI, April 18-23
"Gemini AO Observations of the Extended Sources at the Galactic Center", A. M. Tanner, A.M. Ghez, M. Morris, 2001, Integrating Research and Education, CfAO Workshop, Kona, HI, April 18-23
"High Resolution Study of the Galactic Center Using the Keck Telescopes", A.M. Ghez, A.M. Tanner, S. Gezari, S. Hornstein, D. Sand, 2000, Keck Science Meeting, Santa Cruz, CA, October 18-19.
"Is the Galactic Center Source, IRS 21, as Large as It Appears?" , A.M. Tanner, A.M. Ghez, M. Morris, E.E. Becklin, A. Cotera, M. Werner, Jan. 2001, BAAS, 5.02