Hipparcos Epoch Photometry Research Articles

Directed follow-up strategy of low-cadence photometric surveys in search of transiting exoplanets - I. Bayesian approach for adaptive scheduling

We propose a novel approach to utilize low-cadence photometric surveys for exoplanetary transit search. Even if transits are undetectable in the survey database alone, it can still be useful for finding preferred times for directed follow-up observations that will maximize the chances to detect transits. We demonstrate the approach through a few simulated cases. These simulations are based on the Hipparcos Epoch Photometry data base, and the transiting planets whose transits were already detected there. In principle, the approach we propose will be suitable for the directed follow-up of the photometry from the planned Gaia mission, and it can hopefully significantly increase the yield of exoplanetary transits detected, thanks to Gaia.

The close binary system SU Ind

AbstractPhotometric data on the southern mid‐F type close eclipsing binary system SU Ind from the Carter Observatory (NZ) were examined, together with a light curve obtained from the Hipparcos Epoch Photometry (HEP) database. The system appears detached, although appreciably evolved from the Zero Age Main Sequence. The HEP period must be accurate for its own epoch, but it is significantly different from the reference (Hoffmeister 1956) value. This is difficult to explain, given the uncomplicated nature of the light curve. The apparent discrepancy can be reconciled with a period that has remained almost constant over the 40 year interval between the epochs by assuming some confusion between the almost equal depth minima. The near‐equality of components raises issues of determinacy in light curve analysis, which are reviewed against the presentation of relevant numerical curve‐fitting details. The system is of physical interest, in that it is close to the start of the ‘active’ range of spectral types. Its stars have relatively rapid rotation speeds and probably shallow convective subphotospheric layers. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Short‐Period Variable Be Stars Discovered or Confirmed through Self‐Correlation Analysis of Hipparcos Epoch Photometry

ABSTRACTWe have surveyed 277 bright Be stars for short‐period (0.2–2 day) photometric variability using self‐correlation analysis of Hipparcos epoch photometry. This extends the work of Percy et al.; the methods are as described there. We report the discovery, timescale, and amplitude of short‐period variability in: HD 7636 (V764 Cas), HD 11606 (V777 Cas), HD 13661 (V549 Per), HD 34921, HD 36408, HD 40978, HD 58343 (FW CMa), HD 63460 (o Pup), HD 88195 (17 Sex), HD 89353 (AG Ant, HR 4049), HD 129954 (CO Cir), HD 158220 (V862 Ara), HD 173219 (V947 Sct), and HD 187567 (V1339 Aql). We report the confirmation of short‐period variability using an independent form of analysis in HD 52918 (19 Mon), HD 105382 (V863 Cen), HD 137387 (κ‐1 Aps), HD 157832 (V750 Ara), and HD 163868 (V3984 Sgr). These include a β Cephei star (19 Mon), a Vega‐type star (17 Sex), and a post‐asymptotic giant branch B star (HR 4049). We find that short‐period variability is more prevalent in early‐B stars than in late‐B stars. We have found no β Cephei type variables in our sample of Be stars, other than 19 Mon, which is apparently not a Be star.

Autocorrelation Analysis of Hipparcos Photometry of Short‐Period Be Stars

ABSTRACTWe have used Hipparcos epoch photometry and a form of autocorrelation analysis to investigate the amplitude and timescale of the short‐period variability of 82 Be stars, including 46 Be stars that were analyzed by Hubert & Floquet using Fourier and CLEAN analysis and 36 other Be stars that were suspected of short‐period variability. Our method has given useful information for about 84% of these stars; for the rest, the time distribution of the Hipparcos epoch photometry limits the capability of our technique.

Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars

A selection criterion based on the relative strength of the largest peaks in the amplitude spectra, and an information criterion are used in combination to search for multiperiodicities in Hipparcos epoch photometry. The method is applied to all stars which have been classified as variable in the Hipparcos catalogue: periodic, unsolved and microvariables. Results are assessed critically: although there are many problems arising from aliasing, there are also a number of interesting frequency combinations which deserve further investigation. One such result is the possible occurrence of multiple periods of the order of a day in a few early A-type stars. The Hipparcos catalogue also contains a number of these stars with single periodicities: such stars with no obvious variability classifications are listed, and information about their properties (e.g., radial velocity variations) discussed. These stars may constitute a new class of pulsators.

Mining the Metal‐rich Stars for Planets

We examine the correlation between stellar metallicity and short period planets. It appears that approximately 1% of dwarf stars in the solar neighborhood harbor short-period planets characterized by near-circular orbits and orbital periods P 0.2 dex), it appears that the fraction increases to 10%. Using the Hipparcos database and the Hauck & Mermilliod (1998) compilation of Stromgren uvby photometry, we identify a sample of 206 metal-rich stars of spectral type K, G, and F which have an enhanced probability of harboring short-period planets. Many of these stars would be excellent candidates for addition to radial velocity surveys. We have searched the Hipparcos epoch photometry for transiting planets within our 206 star catalog. We find that the quality of the Hipparcos data is not high enough to permit unambiguous transit detections. It is, however, possible to identify candidate transit periods. We then discuss various ramifications of the stellar metallicity - planet connection. First, we show that there is preliminary evidence for increasing metallicity with increasing stellar mass among known planet-bearing stars. This trend can be explained by a scenario in which planet-bearing stars accrete an average of 30 Earth Masses of rocky material after the gaseous protoplanetary disk phase has ended. We present dynamical calculation which suggest that a survey of metallicities of spectroscopic binary stars can be used to understand the root cause of the stellar metallicity - planet connection.

Another Search for Maia Variable Stars

ABSTRACTWe have used the Hipparcos epoch photometry database, and autocorrelation analysis, to search for the elusive Maia variables—short‐period B7–A3 near–main‐sequence pulsating variable stars. Of several hundred stars considered, and several dozen stars studied in detail, only a handful are possible variables: three are possible shallow eclipsing variables; three have possible periods in the range 0.25–0.5 day, but their amplitudes are so low that they are probably nonvariable. The most promising are HD 29573, with a period of 1.6 days (but possibly a rotating variable), and γ CrB, with a period of 0.9 day—a period also found spectroscopically by Lehmann and coworkers. Sirius shows variations which are probably instrumental. Two previously suspected Maia stars—Maia and γ UMi—are photometrically constant. The Maia variables—if they exist—are very rare and very elusive.

Two Aspects of Using Hipparcos Data for Studying Multiperiodic Stellar Pulsations

AbstractTwo aspects of using Hipparcos data for studying multiperiodic stellar pulsations involve (1) deriving frequencies of multiperiodic pulsators from Hipparcos Epoch Photometry, and (2) using Hipparcos parallaxes together with other data, such as the frequencies, frequency ratios and multicolor photometry, to identify pulsation modes. Details are examined by looking at the δ Scuti star DK Virginis. From Hipparcos Epoch Photometry, two frequencies are derived. These frequencies are then verified by showing that they also fit all available ground-based observations of the star. In addition, Hipparcos parallax and a photometric effective temperature are used to compare the position of DK Vir in the HR diagram with evolutionary tracks. The star turns out to be at the end of core-hydrogen-burning stage of its evolution or slightly beyond, with a mass of 2.2 M⊙, or somewhat smaller. The observed frequencies indicate that the two detected modes are p3 and p2, while the relatively large photometric amplitudes imply ℓ ≲ 2.