Search

Evidence suggesting an observable magnetic interaction between a star and its hot Jupiter (Porb< 7 days,a< 0.1 AU,Mpsini> 0.2MJ) appears as a cyclic variation of stellar activity synchronized to the planet's orbit. HD 179949 has been observed almost every year since 2001. Synchronicity of the Ca II H & K emission with the orbit is clearly seen in four out of six epochs, while rotational modulation withProt=7 days is apparent in the other two seasons. We observe a similar phenomenon on υ And, which displays rotational modulation (Prot=12 days) in September 2005, while in 2002 and 2003 variations appear to correlate with the planet's orbital period. This on/off nature of star-planet interaction (SPI) in the two systems is likely a function of the changing stellar magnetic field structure throughout its activity cycle. The tentative correlation between this activity in the 13 stars we have observed to date and the ratio ofMpsinito the planet's rotation period, a quantity proportional to the hot Jupiter's magnetic moment, first presented in Shkolniket al. (2005) remains viable. This work furthers the characterization of SPI, improving its potential as a probe of extrasolar planetary magnetic fields.

We present precise stellar radial velocity measurements for the K giant star Beta Gem spanning over 25 years. These data show that the long period low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. An examination of the Ca II K emission, spectral line shapes from high resolution data (R = 210,000), and Hipparcos photometry show no significant variations of these quantities with the RV period. These data confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). An orbital solution assuming a stellar mass of 1.7 M_sun yields a period, P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and a semi-major axis, and a = 1.6 AU. The orbit is nearly circular (e = 0.02). Beta Gem is the seventh intermediate mass star shown to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common., 10 pages, 9 figures, Astronomy and Astrophysics, in press

We use precise radial velocity measurements and photometric data to derive the frequency spacing of the p-mode oscillation spectrum of the planet-hosting star Beta Gem. This spacing along with the interferometric radius for this star is used to derive an accurate stellar mass. A long time series of over 60 hours of precise stellar radial velocity measurements of Beta Gem were taken with an iodine absorption cell and the echelle spectrograph mounted on the 2m Alfred Jensch Telescope. Complementary photometric data for this star were also taken with the MOST microsatellite spanning 3.6 d. A Fourier analysis of the radial velocity data reveals the presence of up to 17 significant pulsation modes in the frequency interval 10-250 micro-Hz. Most of these fall on a grid of equally-spaced frequencies having a separation of 7.14 +/- 0.12 micro-Hz. An analysis of 3.6 days of high precision photometry taken with the MOST space telescope shows the presence of up to 16 modes, six of which are consistent with modes found in the spectral (radial velocity) data. This frequency spacing is consistent with high overtone radial pulsations; however, until the pulsation modes are identified we cannot be sure if some of these are nonradial modes or even mixed modes. The radial velocity frequency spacing along with angular diameter measurements of Beta Gem via interferometry results in a stellar mass of M = 1.91 +/- 0.09 solar masses. This value confirms the intermediate mass of the star determined using stellar evolutionary tracks. Beta Gem is confirmed to be an intermediate mass star. Stellar pulsations in giant stars along with interferometric radius measurements can provide accurate determinations of the stellar mass of planet hosting giant stars. These can also be used to calibrate stellar evolutionary tracks., Comment: Accepted by Astronomy and Astrophysics

We present a unique observational study of Spica, a binary system with a primary component of the β Cephei type. We exploit simultaneous high‐resolution spectroscopic observations and high‐precision photometry obtained by the MOST satellite. An important result is that the MOST photometry reveals Spica as an eclipsing binary contrary to what was quoted in the literature.

We have acquired simultaneous high-precision space photometry and radial velocities of the bright hybrid Beta Cep/SPB pulsator Gamma Peg. Frequency analyses reveal the presence of six g modes of high radial order together with eight low-order Beta Cep oscillations in both data sets. Mode identification shows that all pulsations have spherical degrees l = 0 - 2. An 8.5 solar mass model reproduces the observed pulsation frequencies; all theoretically predicted modes are detected. We suggest, contrary to previous authors, that Gamma Peg is a single star; the claimed orbital variations are due to g-mode pulsation. Gamma Peg is the first hybrid pulsator for which a sufficiently large number of high-order g modes and low order p and mixed modes have been detected and identified to be usable for in-depth seismic modeling., Comment: 18 pages (4 pages in journal style), 4 figures, accepted for ApJ Letters

MUSICOS (MUlti-SIte COntinous Spectroscopy) is an international collaboration interested in areas of astronomical research requiring continuous, high-resolution spectroscopy. The MUSICOS stategy has been 1) to organize international campaigns (Catala et al 1993), 2) to build a prototype fibre-fed, high-resolution, echelle spectrograph (Baudrand & Bohm 1992), and 3) to install duplicates of the MUSICOS spectrograph on 2m class telescopes around the world. Stages 1 and 2 have been completed. Preliminary results on θ 2 Tau from the second MUSICOS campaign are presented here.

MOST (Microvariability & Oscillations of STars / Microvariabilite et Oscillations STellaire) is a Canadian microsatellite mission intended to detect rapid photometric oscillations at theμmag level in stars brighter thanV∼ 6. This limit is set primarily by the 15-cm aperture of the MOST telescope. The small size and mass of the MOST bus (similar to a suitcase) sets a limit on the pointing accuracy of about ±10 arcsec. To achieve the required photometric precision under these conditions, the MOST focal plane features a set of Fabry microlenses which can spread the target starlight into a pupil image of the telescope onto a CCD. The large size (∼1600 pixels) and positional stability (±0.1 pixel) of these images makes MOST insensitive to CCD flat-fielding errors. MOST is currently on schedule to be launched in early 2002.

With a 5.4-hour time series of high-resolution CFHT spectra, the oscillations of the rapidly-rotating delta Scuti star Theta2 Tauri (A7 IV + A5 V) are investigated. Line-profile variations are discovered and identified with the spectrum of the primary star of this binary system. Radial velocity variations are derived from the data and analyzed to reveal an oscillation frequency near 13.7 cycles day-1. Variations within the absorption profiles are analyzed with a Fourier-Doppler Imaging (FDI) technique to reveal that high-degree oscillations with a frequency of 16.1 cycles day -1 and an apparent degree of about l = 8 are also present in the star. Whereas the low-degree variations of Theta2 Tau have been shown to be consistent with p-modes of radial order n=2 or 3, the identification of the high-degree variations in terms of pressure modes requires confirmation with theoretical models.

The hydrogen fluoride (HF) absorption cell technique has been used at the Canada-France-Hawaii Telescope for over a decade to monitor the radial velocity variability of nearby, solar-type stars in a search for substellar companions. As a complement to this program, we have also been monitoring a select group of G and K subgiants, giants and supergiants, which have all proved variable. We present here a brief summary of our analysis.

We have determined a precise orbit of Chi-1 Orionis (G0 V, MV = 4.4) using radial velocities observed with our HF absorption-cell technique and previous Sproul astrometric observations. Least-squares analysis yields a photocentric semimajor axis alphap = 0.082 ± 0.004 arc-seconds, a radial-velocity amplitude K = 1886 ± 6 m s-1, and a period P = 14.21 ± 0.06 years. Our results imply the secondary has a mass of 0.15 ± 0.01 solar mass, the minimum parallax of the system is pi = 0.102 ± 0.005 arc-seconds, and the secondary is fainter than MV = 8.8.

Subfeatures at about 0.5 percent of the continuum move from blue to red through the line profiles of the Be/shell star Zeta Tau. They resemble subfeatures observed in other stars thought to be nonradial pulsators and their average spacing (0.095d) and acceleration (1550 km/s per d) are consistent with m = 14 + or - 2. The linewidths vary with a period (0.683d) which is consistent with an l = 2 mode. After removal of ellipsoidal-like variations from the linewidths, a period (0.1097d) which is similar to the average subfeature spacing is also detected. A formulation which corrects for the effects of pulsation on the observed subfeature motion has been derived and used to estimate a consistent stellar radius (9.7 solar radii) and rotation period (1.39d). The shell components of H-beta and H-gamma also show signs of small-amplitude (about 0.5 percent of the continuum) rapid (of the order of a few hours) line-strength variations. 72 refs.

Given here are reports on the scientific and business meetings held in Baltimore involving Commission 9 only. Reports on the following Joint Commission Meetings co-sponsored by Commission 9 (JCM 3 and JCM 6), and on three additional meetings organised jointly with other Commissions, will be found elsewhere in this Volume or in Highlights of Astronomy (Volume 8): - High Angular Resolution Imaging from the Ground (JCM 3) - Stellar Photometry with Array Detectors (JCM 6) - Problems of IR Extinction and Standardization (with Commission 25) - Future Space Programs (with Commission 44) - Gamma-ray, X-ray, Extreme and Far UV, IR and Radio Astronomy from Space (with Commissions 40 and 44)

Relative radial velocities can now be determined with internal errors as small as ~ 10 m s−l. A variety of techniques for achieving this level of precision are either presently running, or will soon be on-line. These could be used on several astronomical frontiers; the most demanding application is the search for extra-solar planetary systems. We briefly review these techniques, and highlight the results obtained to date.

Details are given of a Littrow‐mounted grating spectrometer which uses a cooled linear array of silicon diodes as a detector (0.4–1.1 μ) and an Erfle eyepiece as collimator/camera. The slit is illuminated by a standard 35 mm camera lens. Analog diode output signals are multiplexed, digitized, and either recorded on magnetic tape for later processing or signal‐averaged by a small on‐line computer, then recorded on magnetic tape, and displayed on an oscilloscope. Test data are presented. The device has no moving parts, is competitive with existing devices based on photomultipliers and television cameras, and can be readily modified to increase the number of channels and improve wavelength and spatial resolution and throughput.

Interstellar extinction curves (mext vs. 1/λ) of 20 Å resolution have been obtained at the DAO from photoelectric scanner observations in the range 4000 Å to 5000 Å for five stars, and of 50 Å resolution for four stars in the range 4000 Å to 6500 Å from Willstrop's photoelectric data. There is a closely linear section between 4900 Å and 5800 Å for all of the curves. There are changes of gradient or discontinuities associated with the broadest diffuse interstellar bands at 6180 Å, 4882 Å, 4761 Å and 4430 Å. There is a marked discontinuity near 5800 Å and for some stars a broad absorption near 4200 Å. The 4430 Å band lies between two unequal wings of anomalously low extinction (one of which has been detected at Edinburgh). The irregularities vary from star to star, and those in the neighbourhood of the 4430 Å band seem to have the same form as those in the region of the absorption peak at 2200 Å

High resolution spectral scans of some Be stars, taken with an Isocon television camera, show changes in the Ha line profile in times of the order of a minute or less.

A classification method has been developed for early–type stars observed on the Dominion Astrophysical Observatory photometric system. Two reddening-independent parameters, Q(35) and Q(38), are used. Q(35) is a measure of the Balmer discontinuity, while Q(38) is a measure of the strength of the upper members of the Balmer series. A preliminary calibration of Q(35) and Q(38) in terms of spectral types and luminosity classes is given, and applications to several groups of stars are shown.

We have monitored changes in the radial velocities of 24 bright F, G and K dwarf stars (known spectroscopic binaries excluded) for the past six years at CFHT by imposing the absorption lines of HF gas in the spectra to act as wavelength fiducials. The average external error in the δ(velocities) which are based on some 16 stellar lines is 13 m/s corresponds to 0.6 micron in the spectrum or 0.04 of a diode spacing per line. Reductions are complete for 16 stars. There is no evidence for brown dwarf companions in the sample. Two previously unknown spectroscopic binaries were found, and seven stars show indications of significant, long-term, low-level velocity variations which could be interpreted as purturbations by companions of a few Jupiter masses with periods greater than 12 years except for γ Cep, which may have a period of 2.7 years, and ε Eri. Observing time has been guaranteed for at least two more years at CFHT.

By imposing absorption lines of HF in stellar spectra we can measure changes in r.v. with a precision of ~10m/s from a single spectrum, provided stellar line profiles are not distorted by atmospheric motions. The precision of absolute radial velocities is currently limited to ~100m/s by knowledge of rest wavelengths. Representative results are presented from our three, active PRV programs: velocity variations of δ Scuti stars; a search for unseen companions to late-type stars; and routine observations of certain IAU velocity ‘standards’.

A simultaneous four channel photoelectric photometer has been used successfully by astronomers at the Dominion Astrophysical Observatory in the past three years to measure the colours of some 2000 stars. The optics consist of a small grating spectrograph with quartz lenses. Windows in the focal plane of the camera isolate four spectral regions and the light is fed to separate EMI photomultipliers. The photometer is not designed for very faint star observations, consequently D.C. techniques are used. Although the photomultipliers are not refrigerated, a 2 per cent precision is possible in the measurement of the colours of a star of V = 12 in a 1 min integration with a 16-inch telescope. Provided stars are bright relative to the sky background, measured colours are insensitive (±001) to transparency variations of up to three magnitudes caused by normal light cloud. The outputs of the photomultipliers are integrated on capacitors and timing is controlled by a crystal oscillator. An integrator and associated control circuitry are shown schematically in Figure 1. The integrators are read automatically by a digital voltmeter and the results together with time and other data are punched out on paper tape. A block diagram of the data acquisition system is given in Figure 2. After conversion of the tape to a card deck the data is processed in the computer. The system has proved to be very stable and mean errors in single observations of each colour are between 0004 and 0007. The most time consuming part of the process is in the careful editing and sieving of the results for erroneous data generated by line voltage spikes, mispunches, and observer mistakes.

A classification method has been developed for early—type stars observed on the Dominion Astrophysical Observatory photometric system. Two reddening—independent parameters, Q(35) and Q(38), are used. Q(35) is a measure of the Balmer discontinuity, while Q(38) is a measure of the strength of the upper members of the Balmer series. A preliminary calibration of Q(35) and Q(38) in terms of spectral types and luminosity classes is given, and applications to several groups of stars are shown.

Precise radial velocities have been measured for the δ Scuti variable 20 CVn. The Ca II λ8662 line shows a 2K amplitude of 1.4 km s-1. The weak lines of Fe I, Si I, and S I show a 2K amplitude of 1.2 km s-1. A cycle-count period of 0d.130 is derived from the radial-velocity curves. The low 2K/Δmv value of 39 km s-1mag-1 suggests that 20 CVn is pulsating nonradially.

Subfeatures < 0.5% of continuum were detected moving through the line profiles of the Be/shell star γ Cas over a nine-month period in 1983. While the average spacing and acceleration of the subfeatures is consistent with nonradial pulsation of |m| = 12±4, large variations in the acceleration of the subfeatures are sometimes seen and some subfeatures appear and disappear suddenly. The observed period of the subfeature oscillations varies between 7000 and 10,000 seconds which is similar to the transient 6000-second variation in X-ray flux by EXOSAT in December 1984. No rapid E/C variation is observed in the Hγ and He I λ5876 emission-line profiles.

An area photometer consisting of a square two-dimensional array of 2500 silicon diodes is described which is particularly suitable for the observation of bright objects with a wide range of intensity and also as an astrometric device in very small fields. Results are reported for BVR observations with this photometer of the bright globular cluster M15. A color map of M15 is presented which shows that the brightest stars at the center of the cluster are red and that the nuclear region appears slightly redder than the underlying stellar distribution but not as red as the brightest red giants. A lack of unusual color variations in the central region is noted, and the importance of R photometric maps in isolating red giants from the less luminous underlying population is stressed.

Les donnees d'observations des vitesses radiales relatives de 16 etoiles (12 naines rouges et 4 sous-geantes) sont analysees en detail pour tenter de detecter la presence de composantes planetaires (de type naine brune par exemple).Deux d'entre elles, χ 1 ori A et γ Cep presentent de grandes variations de vitesses (quelques km/s) probablement causees par des compagnons stellaires. Sept autres etoiles presentent de petites variations a long terme dont l'attribution a des composantes secondaires ayant plusieurs fois la masse de Jupiter est discutee

Observations were made with a 1.2-m telescope coude spectrograph and an Image Isocon camera of the spectrum of X Per at 4686 A and H beta to look for 13.9-minute periodic changes, observed previously in the X-ray source 3U 0352 plus 30, in order to confirm the optical identification. From the data, it appears that over regions of 2 A or less, associated with these wavelengths, periodic changes modulo 13.9 minutes are not seen above the 2 percent level. Changes below this level are indicated in the power spectra, but are not of high statistical significance.

The Mv-W(H-gamma) calibration of main-sequence stars of Millward and Walker (1985) is evaluated by observing bright supergiants in clusters. Fifty-two spectra of 39 O, B, and A supergiants combined with 19 higher dispersion spectra of 18 stars are studied. Wing profiles were generated by fitting a two-component, absorption-coefficient model to the H-gamma profiles. The calculated Mv data are compared to photometric values. It is observed that there is a difference in the present calibration and the Millward and Walker calibration due to the manner in which the wing profiles are defined; however, the nonlinear relation between the spectral types and W(H-gamma) found by Millward and Walker is confirmed.

Differential polarization measurements in the region of the diffuse feature at 6284 A in the spectrum of HD 183143 are described. The observations were made using a television detector and a Polaroid filter. No systematic change through the diffuse feature was observed, and an upper limit of plus-or- minus0.4 percent is placed on the variation of polarization in the spectral region.

Subfeatures of Omicron And at not greater than 0.5 percent of the continuum traveling through the rotationally broadened absorption lines of the primary are reported. The apparent magnitude of the A component is found to be 3.8 + or - 0.1. The results show that the spectral type of Omicron And A is closer to B5 than B6, and that the luminosity class is II-III. A spectrophotometric distance to Omicron And of 188 + or - 27 pc is obtained.

Precision radial velocities with a time resolution of 15 min (P/10) are measured for Beta Cas (P = 2h30m) over almost two cycles using the HF absorption-cell technique. The precision of + or - 0.2 km/s is limited by line-profile variations not by the technique. The Ca II 8662 A line exhibits the largest amplitude (+ or - 2.3 km/s) in comparison with the HI, P12 line and weak metallic lines of S I, Si I, Mg I and Fe I, which have amplitudes of + or - 2 km/s and + or - 1.6 km/s, respectively. The period of 0.0976 day derived from the Ca II velocity curve agrees with the photometric period of 0.104 day. The H I velocity minima lag by some 2% in phase compared with the Ca II and metallic-line velocity curves; this is similar to the van Hoof effect in Beta CMa variables. The Ca II line shows broad and narrow phases that coincide with the phases of minimum and maximum velocity, respectively. Details are given of the HF reference line technique.

From Reticon spectra of about 1 A resolution taken between 1980 and 1984, the radial velocity curve of HDE 226868 is found to be characteristic of a single-line spectroscopic binary with K = 75.0 + or - 1.0 km/s and e = 0.0. Combining historical velocities from the literature with present data and applying a period-folding analysis, a period of 5.59964 + or - 0.00001 days is found. These values agree well with those published by Gies and Bolton (1982). The value of v sin i is estimated to be 94.3 + or - 5 km/s from CFHT Reticon spectra taken at 0.1 A resolution. Assuming that the rotation of the primary is synchronized to the orbital revolution of the secondary gives a primary to secondary mass ratio between 1.5 and 2.3. An absolute magnitude of -6.5 + or - 0.2 is derived from the equivalent width of H-gamma (1.5 + or - 0.1 A) and the calibration of Walker and Millward (1985), which is consistent with the spectral classification of O9.7 Iab. Assuming 20 solar masses as a reasonable estimate for the mass of the primary implies a mass of 10 + or - 1 solar masses for themore » secondary. 62 references.« less

The equivalent width of the H and K emission reversals of A And showed significant variations relative to the continuum in ten spectrograms taken over a 15-month period. The spectrograms were obtained with a television detector. The variations are not correlated with the 21-day spectroscopic period but do show some correlation with the 56-day photometric period found by Archer which implies that the variations may be related to the luminosity variations of the star. The data are insufficient to establish this and the variations may in fact be irregular. High-resolution spectra of the K line indicated that there are no shortterm variations in excess of 5% over a period of one hour. Key words: emission lines - spectrophotometry

Etude de 4 variables delta Scuti en rotation rapide (∼120 km s −1 ): omicron 1 Eri, K 2 Boo, nu UMa et 21 Mon

Greenstein and Munch1, and Sargent and Searle2, have recently shown that the atmospheric helium abundance in the halo and globular cluster B stars is low compared with that for normal B stars in the Galaxy. Greenstein, Truran and Cameron3 have suggested that the low abundance may be the result of gravitational diffusion of helium from the atmosphere to a lower layer within the star. They consider that normally mixing currents set up by stellar rotation would counteract such diffusion. In contrast to galactic disk B stars, most of the halo stars appear to be slow rotators. This result is apparently confirmed by Sargent and Strittmatter4, who have discussed the weak helium line stars in Orion and conclude that they are intrinsically slow rotators, and that the anomaly is an atmospheric one.