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T. Mazeh

Publications and source records attributed to T. Mazeh.

106 records · Page 6Linked to original sources
arXiv2004

An Upper Bound on the Flux Ratio of rho CrB's Companion at 1.6um

We use high resolution infrared spectroscopy to investigate the 2001 report by Gatewood and colleagues that rho CrB's candidate extrasolar planet companion is really a low-mass star with mass 0.14+-0.05 Msun. We do not detect evidence of such a companion; the upper bounds on the (companion/primary) flux ratio at 1.6 microns are less than 0.0024 and 0.005 at the 90 and 99% confidence levels, respectively. Using the H-band mass-luminosity relationship calculated by Baraffe and colleagues, the corresponding upper limits on the companion mass are 0.11 and 0.15 Msun. Our results indicate that the infrared spectroscopic technique can detect companions in binaries with flux ratios as low as 0.01 to 0.02.

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arXiv2004

A low-mass stellar companion of the planet host star HD75289

We report on the detection of a new low-mass stellar companion of HD75289, a G0V star that harbors one known radial-velocity planet (Udry et al. 2000). Comparing an image of 2MASS with an image we obtained with SofI at the ESO 3.58m NTT three years later, we detected a co-moving companion located 21.465+-0.023arcsecs (621+-10AU at 29pc) east of HD75289. A second SofI image taken 10 months later confirmed the common proper motion of HD75289B with its host star. The infrared spectrum and colors of the companion are consistent with an M2 to M5 main-sequence star at the distance of HD75289. No further (sub)stellar companion down to H = 19mag could be detected. With the SofI detection limit we can rule out additional stellar companions beyond 140AU and substellar companions with masses m > 0.050Msun from 400AU up to 2000AU.

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arXiv2004

Astrometric confirmation of a wide low-mass companion to the planet host star HD89744

In our ongoing deep infrared imaging search for faint wide secondaries of planet-candidate host stars we have confirmed astrometrically the companionship of a low-mass object to be co-moving with HD89744, a companion-candidate suggested already by Wilson et al. (2000). The derivation of the common proper motion of HD89744 and its companion, which are separated by 62.996+-0.035 arcsec, is based on about 5 year epoch difference between 2MASS and our own UKIRT/UFTI images. The companion effective temperature is about 2200 K and its mass is in the range between 0.072 and 0.081 Msun, depending on the evolutionary model. Therefore, HD89744B is either a very low mass stellar or a heavy brown dwarf companion.

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arXiv2004

A search for wide (sub)stellar companions around extrasolar planet host stars

We present an overview of our ongoing systematic search for wide (sub)stellar companions around the stars known to host rad-vel planets. By using a relatively large field of view and going very deep, our survey can find all directly detectable stellar and massive brown dwarf companions (m>40 Mjup) within a 1000 AU orbit.

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arXiv2003

The Mass Ratio Distribution in Main-Sequence Spectroscopic Binaries Measured by IR Spectroscopy

We report infrared spectroscopic observations of a large, well-defined sample of main-sequence, single-lined spectroscopic binaries in order to detect the secondaries and derive the mass ratio distribution of short-period binaries. The sample consists of 51 Galactic disk spectroscopic binaries found in the Carney and Latham high-proper-motion survey, with primary masses in the range of 0.6--0.85 msun. Our infrared observations detect the secondaries in 32 systems, two of which have mass ratios, q=M_2/M_1, as low as ~0.20. Together with 11 systems previously identified as double-lined binaries by visible light spectroscopy, we have a complete sample of 62 binaries, out of which 43 are double-lined. The mass ratio distribution is approximately constant over the range q=1.0 to 0.3. The distribution appears to rise at lower q values, but the uncertainties are sufficiently large that we cannot rule out a distribution that remains constant. The mass distribution derived for the secondaries in our sample, and that of the extra-solar planets, apparently represent two distinct populations.

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arXiv2003

Multi-order TODCOR: application to observations taken with the CORALIE echelle spectrograph

This paper presents an application of the TwO-Dimensional CORrelation (TODCOR) algorithm to multi-order spectra. The combination of many orders enables the detection and measurement of the radial velocities of very faint companions. The technique is first applied here to the case of HD41004, where the secondary is 3.68 magnitudes fainter than the primary in the V band. When applied to CORALIE spectra of this system, the technique measures the secondary velocities with a precision of 0.6 km/s and facilitates an orbital solution of the HD41004B subsystem. The orbit of HD41004B is nearly circular, with a companion of a 19 Jupiter masses (minimum mass). The precision achieved for the primary is 10 m/s, allowing the measurement of a long-term trend in the velocities of HD41004A.

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arXiv2002

Component Masses of the Young Spectroscopic Binary UZ Tau E

We report estimates of the masses of the component stars in the pre-main-sequence spectroscopic binary UZ Tau E. These results come from the combination of our measurements of the mass ratio, M2/M1=0.28 +/-0.01, obtained using high resolution H-band spectroscopy, with the total mass of the system, (1.31 +/-0.08)(D/140pc) M_sun, derived from millimeter observations of the circumbinary disk (Simon et al. 2000). The masses of the primary and secondary are (1.016 +/-0.065)(D/140pc) M_sun and (0.294 +/-0.027)(D/140pc) M_sun, respectively. Using the orbital parameters determined from our six epochs of observation, we find that the inclination of the binary orbit, 59.8 +/-4.4 degrees, is consistent with that determined for the circumbinary disk from the millimeter observations, indicating that the disk and binary orbits are probably coplanar.

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arXiv2002

A box-fitting algorithm in the search for periodic transits

We study the statistical characteristics of a box-fitting algorithm to analyze stellar photometric time series in the search for periodic transits by extrasolar planets. The algorithm searches for signals characterized by a periodic alternation between two discrete levels, with much less time spent at the lower level. We present numerical as well as analytical results to predict the possible detection significance at various signal parameters. It is shown that the crucial parameter is the effective signal-to-noise ratio -- the expected depth of the transit divided by the standard deviation of the measured photometric average within the transit. When this parameter exceeds the value of 6 we can expect a significant detection of the transit. We show that the box-fitting algorithm performs better than other methods available in the astronomical literature, especially for low signal-to-noise ratios.

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arXiv2002

The Smallest Mass Ratio Young Star Spectroscopic Binaries

Using high resolution near-infrared spectroscopy with the Keck telescope, we have detected the radial velocity signatures of the cool secondary components in four optically identified pre-main-sequence, single-lined spectroscopic binaries. All are weak-lined T Tauri stars with well-defined center of mass velocities. The mass ratio for one young binary, NTTS 160905-1859, is M2/M1 = 0.18+/-0.01, the smallest yet measured dynamically for a pre-main-sequence spectroscopic binary. These new results demonstrate the power of infrared spectroscopy for the dynamical identification of cool secondaries. Visible light spectroscopy, to date, has not revealed any pre-main-sequence secondary stars with masses <0.5 M_sun, while two of the young systems reported here are in that range. We compare our targets with a compilation of the published young double-lined spectroscopic binaries and discuss our unique contribution to this sample.

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arXiv2001

A Planet Candidate in the Stellar Triple System HD178911

We report the detection of a low-mass companion orbiting the solar-type star HD178911B, the distant component of the stellar triple system HD178911. The variability of HD178911B was first detected using radial-velocity measurements obtained with the HIRES spectrograph mounted on the 10-m Keck1 telescope at the W.M. Keck Observatory (Hawaii, USA). We then started an intense radial-velocity follow up of the star with the ELODIE echelle spectrograph mounted on the 1.93-m telescope at the Observatoire de Haute-Provence (France) in order to derive its orbital solution. The detected planet candidate has an orbital period of 71.5 days and a minimum mass of 6.3 Jupiter masses. We performed a spectral analysis of the star, which shows that the lithium abundances in the system are similar to those in another known planet-hosting wide binary stellar system, 16 Cyg. In both systems the lithium is undetected in the atmosphere of the visual secondary harboring the planetary companion, but is easily detected in the spectrum of the visual primary. We discuss this similarity and its ramifications.

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arXiv2001

IR Detection of Low-Mass Secondaries in Spectroscopic Binaries

This paper outlines an infrared spectroscopic technique to measure the radial velocities of faint secondaries in known single-lined binaries. The paper presents our H-band observations with the CSHELL and Phoenix spectrographs and describes detections of three low-mass secondaries in main-sequence binaries: G147-36, G164-67, and HD144284 with mass ratios of 0.562+-0.011, 0.423+-0.042, and 0.380+-0.013, respectively. The latter is one of the smallest mass ratios derived to date.

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arXiv2001

HD 80606 b, a planet on an extremely elongated orbit

We report the detection of a planetary companion orbiting the solar-type star HD 80606, the brighter component of a wide binary with a projected separation of about 2000 AU. Using high-signal spectroscopic observations of the two components of the visual binary, we show that they are nearly identical. The planet has an orbital period of 111.8 days and a minimum mass of 3.9 M_Jup. With e=0.927, this planet has the highest orbital eccentricity among the extrasolar planets detected so far. We finally list several processes this extreme eccentricity could result from.

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arXiv2001

A Dynamical Mass Constraint for Pre-Main-Sequence Evolutionary Tracks: The Binary NTT 045251+3016

We present an astrometric/spectroscopic orbital solution for the pre-main-sequence binary NTT 045251+3016. Our measurements for the primary and secondary masses are 1.45 +/- 0.19 M_sun and 0.81 +/- 0.09 M_sun, respectively, and 145 +/- 8 pc for the distance of the system, consistent with prior estimates for the Taurus-Auriga star-forming region. The evolutionary tracks of D'Antona & Mazzitelli (1997), Baraffe et al. (1998), and Palla & Stahler (1999) are tested against these dynamical mass measurements. Due to the intrinsic color/T_eff variation within the K5 spectral class, each pre-main-sequence model provides a mass range for the primary. The theoretical mass range derived from the Baraffe et al. (1998) tracks that use a mixing length parameter alpha=1.0 is closest to our measured primary mass, deviating between 1.3 and 1.6 sigma. The set of Baraffe et al. (1998) tracks that use alpha=1.9 deviate between 1.6 and 2.1 sigma from our measured primary mass. The mass range given by the Palla & Stahler (1999) tracks for the primary star deviate between 1.6 and 2.9 sigma. The D'Antona & Mazzitelli (1997) tracks give a mass range that deviates by at least 3.0 sigma from our derived primary mass, strongly suggesting that these tracks are inconsistent with our observation. Observations of the secondary are less constraining than those of the primary, but the deviations between the dynamical mass of the secondary and the mass inferred for the secondary from the various pre-main-sequence tracks mirror the deviations of the primary star. All of the pre-main-sequence tracks are consistent with coevality of the components of NTT 045251+3016.

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arXiv2000

Comparison Between Extrasolar Planets and Low-Mass Secondaries

This paper compares the statistical features of the sample of discovered extrasolar planets with those of the secondaries in nearby spectroscopic binaries, in order to enable us to distinguish between the two populations. Based on 32 planet candidates discovered until March 2000, we find that their eccentricity and period distribution are surprisingly similar to those of the binary population, while their mass distribution is remarkably different. The mass distributions definitely support the idea of two distinct populations, suggesting the planet candidates are indeed extrasolar planets. The transition between the two populations probably occurs at 10--30 Jupiter masses. We point out a possible negative correlation between the orbital period of the planets and the metallicity of their parent stars, which holds only for periods less than about 100 days. These short-period systems are characterized by circular or almost circular orbits.

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arXiv2000

The Spectroscopic Orbit of the Planetary Companion Transiting HD209458

We report a spectroscopic orbit with period P = 3.52433 +/- 0.00027 days for the planetary companion that transits the solar-type star HD209458. For the metallicity, mass, and radius of the star we derive [Fe/H] = 0.00 +/- 0.02, M = 1.1 +/- 0.1 solar masses, and R = 1.3 +/- 0.1 solar radii. This is based on a new analysis of the iron lines in our HIRES template spectrum, and also on the absolute magnitude and color of the star, and uses isochrones from four different sets of stellar evolution models. Using these values for the stellar parameters we reanalyze the transit data and derive an orbital inclination of i = 85.2 +/- 1.4 degrees. For the planet we derive a mass of Mp = 0.69 +/- 0.05 Jupiter masses, a radius of Rp = 1.54 +/- 0.18 Jupiter radii, and a density of 0.23 +/- 0.08 grams per cubic cm.

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