Suvrath Mahadevan

The First Extrasolar Planet Discovered with a New-Generation High-Throughput Doppler Instrument

We report the detection of the first extrasolar planet, ET-1 (HD 102195b), using the Exoplanet Tracker (ET), a new-generation Doppler instrument. The planet orbits HD 102195, a young star with solar metallicity that may be part of the local association. The planet imparts radial velocity variability to the star with a semiamplitude of 63.4 ± 2.0 m s-1 and a period of 4.11 days. The planetary minimum mass (m sin i) is 0.488MJ ± 0.015MJ. The planet was initially detected in the spring of 2005 with the Kitt Peak National Observatory (KPNO) 0.9 m coude feed telescope. The detection was confirmed by radial velocity observations with the ET at the KPNO 2.1 m telescope and also at the 9 m Hobby-Eberly Telescope (HET) with its High Resolution Spectrograph. This planetary discovery with a 0.9 m telescope around a V = 8.05 magnitude star was made possible by the high throughput of the instrument: 49% measured from the fiber output to the detector. The ETs interferometer-based approach is an effective method for planet detection. In addition, the ET concept is adaptable to multiple-object Doppler observations or very high precision observations with a cross-dispersed echelle spectrograph to separate stellar fringes over a broad wavelength band. In addition to spectroscopic observations of HD 102195, we obtained brightness measurements with one of the automated photometric telescopes at Fairborn Observatory. Those observations reveal that HD 102195 is a spotted variable star with an amplitude of ~0.015 mag and a 12.3 ± 0.3 day period. This is consistent with spectroscopically observed Ca II H and K emission levels and line-broadening measurements but inconsistent with rotational modulation of surface activity as the cause of the radial velocity variability. Our photometric observations rule out transits of the planetary companion.

The Use of Absorption Cells as a Wavelength Reference for Precision Radial Velocity Measurements in the Near-Infrared

Considerable interest is now focused on the detection of terrestrial mass planets around M dwarfs, and radial velocity surveys with high-resolution spectrographs in the near-infrared (NIR) are expected to be able to discover such planets. We explore the possibility of using commercially available molecular absorption gas cells as a wavelength reference standard for high-resolution fiber-fed spectrographs in the NIR. We consider the relative merits and disadvantages of using such cells compared with thorium-argon emission lamps and conclude that in the astronomical H band, they are a viable method of simultaneous calibration, yielding an acceptable wavelength calibration error for most applications. Four well-characterized and commercially available standard gas cells of H13C14N, 12C2H2, 12CO, and 13CO can together span over 120 nm of the H band, making them suitable for use in astronomical spectrographs. The use of isotopologues of these molecules can increase line densities and wavelength coverage, extending their application to different wavelength regions.

A new generation multi-object Doppler instrument for the SDSS-III Multi-object APO Radial Velocity Exoplanet Large-area Survey

We report performance of a new generation multi-object Doppler instrument for the on-going Multi-object APO Radial-velocity Exoplanet Large-area Survey (MARVELS) of the Sloan Digital Sky Survey III (SDSS-III) program. This instrument is based on dispersed fixed-delay interferomtry design. It consists of a multi-object fiber-feed, a thermally compensated monolithic fixed-delay interferometer, a high throughput spectrograph and a 4kx4k CCD camera. The spectrograph resolving power is R=11,000 and the wavelength coverage is 500-570 nm. The instrument is capable of measuring 60 stars in a single exposure for high to moderate precision radial velocity (3-20 m/s) measurements depending on the star magnitudes (V=7.6-12). The instrument was commissioned at the SDSS telescope in September 2008 and used to collect science data starting in October 2008. Observations of reference stars show that the measured photon noise limiting errors are consistent with the prediction for most of the measurements.

MEASURING STELLAR RADIAL VELOCITIES WITH A DISPERSED FIXED-DELAY INTERFEROMETER

We demonstrate the ability to measure precise stellar barycentric radial velocities with the dispersed fixed-delay interferometer technique using the Exoplanet Tracker (ET), an instrument primarily designed for precision differential Doppler velocity measurements using this technique. Our barycentric radial velocities, derived from observations taken at the KPNO 2.1 m telescope, differ from those of Nidever et al. by 0.047 km s−1 (rms) when simultaneous iodine calibration is used, and by 0.120 km s−1 (rms) without simultaneous iodine calibration. Our results effectively show that a Michelson interferometer coupled to a spectrograph allows precise measurements of barycentric radial velocities even at a modest spectral resolution of R ~ 5100. A multiobject version of the ET instrument capable of observing ~500 stars per night is being used at the Sloan 2.5 m telescope at Apache Point Observatory for the Multiobject APO Radial Velocity Exoplanet Large-area Survey (MARVELS), a wide-field radial velocity survey for extrasolar planets around TYCHO-2 stars in the magnitude range 7.6 < V < 12. In addition to precise differential velocities, this survey will also yield precise barycentric radial velocities for many thousands of stars using the data analysis techniques reported here. Such a large kinematic survey at high velocity precision will be useful in identifying the signature of accretion events in the Milky Way and understanding local stellar kinematics, in addition to discovering exoplanets, brown dwarfs, and spectroscopic binaries.

Discovery of a Low-Mass Companion to the Solar-Type Star TYC 2534-698-1

Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main-sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M⊙ and an orbital period of ~103 days for the companion. Photometry outside of the transit window shows the star to be stable to within ~6 millimags. The semimajor axis of the orbit places the companion in the brown dwarf desert and we discuss potential follow-up observations that could constrain the mass of the companion.

PRL advanced radial-velocity all-sky search (PARAS): an efficient fiber-fed spectrograph for planet searches

We present here the optical design of an efficient Fiber-fed, Prism Cross-dispersed, Echelle Spectrograph (Resolution ~70,000 @seeing limited ~2arcsecs conditions) which will operate in the wavelength region of 3700A to 8100A. It will be used for extra-solar planets searches down to the precision of 3m/s and as well as for follow-up observations for new transit discoveries. The spectrograph design is such that with a beam size of 100mm (4inch) it should suit the existing 1 to 2m class of telescopes available in India. The fiber-fed spectrograph will be installed with a 1.2m telescope, which is situated at Mt. Abu (5800feet), Rajasthan, India. We estimate the spectrograph to be >30% efficient from the slit to the CCD detector, and up to 15% efficient including sky, telescope, fiber-fed optics etc. We expect to reach the S/N ratio of 70 on a 10mag star for an integration time of 40mins. We aim to achieve 5m/s to 3m/s Radial Velocity accuracies on such a star using the simultaneous ThAr referencing method. Since thermal stability is absolutely necessary to achieve <5m/s RV accuracies, the whole spectrograph is planned to be kept inside a vibration free isolated tank under low vacuum (0.001 mbar) in a thermally isolated room at 28C +/- 0.01C. It should see the first light by the summer of 2009. We are guaranteed at least 120 nights per year for the planet search program, more nights are possible.

The first high resolution silicon immersion grating spectrograph

We report the development of the first high resolution cross-dispersed silicon immersion grating spectrometer. This instrument is called the Florida IR Silicon immersion grating specTrometer (FIRST). FIRST can produce R = 50,000 under a 0.6 arcsec seeing and simultaneously cover 1.3-1.8 μm with a 1kx1k HgCdTe array at the Apache Point Observatory 3.5 meter telescope. FIRST has a 50 mm diameter collimated beam and the overall instrument is within a volume of 0.8x0.5x0.5 m3. The high dispersion, large wavelength coverage and small instrument volume become possible due to the use of a silicon immersion grating (54.7 deg blaze angle and 50 mm diameter entrance pupil) with extremely high dispersion power (3.4 times dispersion power of a conventional echelle) and coarse grooves (16.1 l/mm, coarser than the commercially available echelles). The silicon immersion grating used in a lab bench mounted Czeney-Turner spectrograph with an only 25 mm diameter collimated beam and a 100 um core fiber has produced R = 55,000 cross-dispersed solar spectra. This instrument is designed to precisely measure radial velocities of low mass stars, M dwarfs for detecting 5-10 Earth mass planets. The estimated Doppler precision is ~ 3 m/s for a J = 9 M5V dwarf in 15 min at the APO 3.5m telescope.

A New Generation Multi-object High Throughput Doppler Instrument for a Planet Survey at the SDSS Telescope

We report the design of a new generation multi-object high throughput Doppler instrument and first light results at the Sloan Digital Sky Survey (SDSS) telescope. This instrument, capable of simultaneously monitoring 60 stars for planet detection, is called the W.M. Keck Exoplanet Tracker (or Keck ET) thanks to the generous gift from the W.M. Keck Foundation. It is designed for a planet survey around hundreds of thousands of stars with V =8-13 for detecting tens of thousands of planets in 2006-2020. The Doppler precision is between 3-25 m/s depending on the star magnitude. We also report a new planet detected with a prototype single object version ET instrument at the KPNO Coude Feed/2.1 m telescopes. The extrasolar planet, ET-1 (HD 102195b), has a minimum mass of 0.49 Jupiter masses and orbits a V = 8.1 G8V star with a 4.1 day period. The planet was identified using the Coude Feed 0.9 meter telescope in spring 2005. This is the first time an extrasolar planet around a star fainter than V=8 magnitude has been discovered with an under 1 meter size astronomical telescope and Doppler instrument. This planet discovery is possible due to the extremely high throughput of the instrument, 49% measured from the fiber output end to the detector.

The Habitable-Zone Planet Finder: improved flux image generation algorithms for H2RG up-the-ramp data

Noise and stability of current state of the art near-infrared (NIR) array detectors are still substantially worse than optical science grade CCDs used in astronomy. Obtaining the maximum signal-to-noise ratio in flux image is important for many NIR instruments, as is stable well understood data reduction and extraction. The Habitable- zone Planet Finder (HPF) is a near-infrared ultra stable precision radial velocity (RV) spectrograph commissioned on 10-m Hobby-Eberly Telescope (HET), McDonald Observatory, Texas, USA. HPF uses a Teledyne H2RG array detector. In order to achieve the high-precision (~ 1 m/s) RV measurements from the NIR spectrum of HPFs science target stars, it is vital to maximize the signal-to-noise ratio and to accurately propagate the uncertainties. Here we present the algorithms we have developed to significantly improve the quality of flux images calculated from the up-the-ramp readout mode of H2RG. The algorithms in the tool HxRGproc presented in this manuscript are used for HPFs bias noise removal, non-linearity correction, cosmic ray correction, slope/flux and variance image calculation.

The NEID precision radial velocity spectrometer: port adapter overview, requirements, and test plan

The NEID spectrometer is an optical (380-930 nm), fiber-fed, precision Doppler spectrometer currently in de- velopment for the WIYN 3.5 m telescope at Kitt Peak National Observatory as part of the NN-EXPLORE partnership. Designed to achieve a radial velocity precision of < 30 cm/s, NEID will be sensitive enough to detect terrestrial-mass exoplanets around low-mass stars. Light from the target stars is focused by the telescope to a bent Cassegrain port at the edge of the primary mirror mechanical support. The specialized NEID “Port Adapter” system is mounted at this bent Cassegrain port and is responsible for delivering the incident light from the telescope to the NEID fibers. In order to provide stable, high-quality images to the science instrument, the Port Adapter houses several sub-components designed to acquire the target stars, correct for atmospheric dis- persion, stabilize the light onto the science fibers, and calibrate the spectrometer by injecting known wavelength sources such as a laser frequency comb. Here we provide an overview of the overall opto-mechanical design and system requirements of the Port Adapter. We also describe the development of system error budgets and test plans to meet those requirements.