arXiv subjects

J. H. Telting

Publications and source records attributed to J. H. Telting.

46 records · Page 3Linked to original sources

arXiv2010

Ground-based observations of Kepler asteroseismic targets

We present the ground-based activities within the different working groups of the Kepler Asteroseismic Science Consortium (KASC). The activities aim at the systematic characterization of the 5000+ KASC targets, and at the collection of ground-based follow-up time-series data of selected promising Kepler pulsators. So far, 36 different instruments at 31 telescopes on 23 different observatories in 12 countries are in use, and a total of more than 530 observing nights has been awarded. (Based on observations made with the Isaac Newton Telescope, William Herschel Telescope, Nordic Optical Telescope, Telescopio Nazionale Galileo, Mercator Telescope (La Palma, Spain), and IAC-80 (Tenerife, Spain). Also based on observations taken at the observatories of Sierra Nevada, San Pedro Martir, Vienna, Xinglong, Apache Point, Lulin, Tautenburg, Loiano, Serra la Nave, Asiago, McDonald, Skinakas, Pic du Midi, Mauna Kea, Steward Observatory, Mt Wilson, Bialkow Observatory of the Wroclaw University, Piszkesteto Mountain Station, Observatoire de Haute Provence, and Centro Astronomico Hispano Aleman at Calar Alto. Based on data from the AAVSO International Database.)

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arXiv2010

A survey for pulsating subdwarf B stars with the Nordic Optical Telescope

A search programme for pulsating subdwarf B stars was conducted with the Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009. The purpose of the programme was to significantly extend the number of rapidly pulsating sdB stars to better understand the properties of this new group of variable compact stars. Candidates were selected initially from the HS and HE surveys, but were supplemented with additional objects from other surveys. Short sequences of time-series photometry were made on the candidates to determine the presence of rapid pulsations. In total twenty new pulsators were found in this survey, most of which have already been published and some extensively studied. We present four new short period pulsators, bringing the total of such pulsators up to 49. We also give limits on pulsation amplitudes for 285 objects with no obvious periodic variations, summarise the results of the survey, and provide improved physical parameters on the composite pulsators for which only preliminary estimates were published earlier.

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arXiv2008

Time-series Spectroscopy and Photometry of the Pulsating Subdwarf B Star PG 1219+534 (KY UMa)

We present observations and analysis of time-series spectroscopy and photometry of the pulsating subdwarf B star PG 1219+534 (KY UMa). Subdwarf B stars are blue horizontal branch stars which have shed most of their hydrogen envelopes. Pulsating subdwarf B stars allow a probe into this interesting phase of evolution. Low resolution spectra were obtained at the Nordic Optical Telescope and Kitt Peak National Observatory, and photometric observations were obtained at MDM and Baker observatories in 2006. We extracted radial velocity and equivalent width variations from several Balmer and He I lines in individual spectra. The pulsation frequencies were separated via phase binning to detect line-profile variations in Balmer and helium lines, which were subsequently matched to atmospheric models to infer effective temperature and gravity changes throughout the pulsation cycle. From the photometry we recovered the four previously observed frequencies and detected a new fifth frequency. From the spectra we directly measured radial velocity and equivalent width variations for the four main frequencies and from atmospheric models we successfully inferred temperature and gravity changes for these four frequencies. We compared amplitude ratios and phase differences of these quantities and searched for outliers which could be identified as high-degree modes. These are the first such measurements for a "normal" amplitude pulsating subdwarf B star, indicating that spectroscopic studies can benefit the majority of pulsating subdwarf B stars.

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arXiv2007

Multiperiodicity in the newly discovered mid-late Be star V2104 Cygni

We obtained the first long, homogenous time-series of V2104Cyg, consisting of 679 datapoints, with the uvbybeta photometers of Sierra Nevada and San Pedro Martir Observatories with the aim to detect and subsequently interpret the intrinsic frequencies of this previously unstudied variable star, which turned out to be a Be star. We try to figure out its place among the variable B stars on the upper Main Sequence. In order to obtain additional information on physical parameters we collected a few spectra with the ELODIE and FIES instruments. We searched for frequencies in the uvby passbands using 2 different frequency analysis methods and used the S/N>4 criterion to select the significant periodicities. We obtained an estimate of the physical parameters of the underlying B star of spectral type between B5 and B7, by correcting for the presence of a circumstellar disk, using a formalism based on the strenght of the Halpha line emission. We detected 3 independent frequencies with amplitudes below 0.01mag, f1 = 4.7126 c/d, f2 = 2.2342 c/d and f3 = 4.671 c/d, and discovered that V2104Cyg is a Be star. The fast rotation (vsini=290+/-10 km/s, and 27<i<45) hampered the investigation of the associated pulsational parameters l. Nevertheless, the most plausible explanation for the observed variability of this mid-late type Be star is a non-radial pulsation model. This paper is based on observations obtained at the Observatorio Astronomico Nacional San Pedro Martir (Mexico), Observatorio de Sierra Nevada (Spain), Observatoire de Haute Provence (France), and on observations made with the Nordic Optical Telescope, Observatorio Roque de los Muchachos, La Palma, Spain.

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arXiv2006

On the H$α$ emission from the $β$ Cephei system

Be stars, which are characterised by intermittent emission in their hydrogen lines, are known to be fast rotators. This fast rotation is a requirement for the formation of a Keplerian disk, which in turn gives rise to the emission. However, the pulsating, magnetic B1IV star $β$ Cephei is a very slow rotator that still shows H$α$ emission episodes like in other Be stars, contradicting current theories. We investigate the hypothesis that the H$α$ emission stems from the spectroscopically unresolved companion of $β$ Cep. Spectra of the two unresolved components have been separated in the 6350-6850Årange with spectro-astrometric techniques, using 11 longslit spectra obtained with ALFOSC at the Nordic Optical Telescope, La Palma. We find that the H$α$ emission is not related to the primary in $β$ Cep, but is due to its 3.4 magnitudes fainter companion. This companion has been resolved by speckle techniques, but it remains unresolved by traditional spectroscopy. The emission extends from about $-$400 to +400 km s$^{-1}$. The companion star in its 90-year orbit is likely to be a classical Be star with a spectral type around B6-8. By identifying its Be-star companion as the origin of the H$α$ emission behaviour, the enigma behind the Be status of the slow rotator $β$ Cep has been resolved.

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arXiv2005

The orbit of the close spectroscopic binary epsilon Lupi and the intrinsic variability of its early B-type components

We subjected 106 new high-resolution spectra of the double-lined spectroscopic close binary epsilon Lupi, obtained in a time-span of 17 days from two different observatories, to a detailed study of orbital and intrinsic variations. We derived accurate values of the orbital parameters. We refined the sidereal orbital period to 4.55970 days and the eccentricity to e=0.277. By adding old radial velocities, we discovered the presence of apsidal motion with a period of the rotation of apses of about 430 years. Such a value agrees with theoretical expectations. Additional data is needed to confirm and refine this value. Our dataset did not allow us to derive the orbit of the third body, which is known to orbit the close system in approximately 64 years. We present the secondary of epsilon Lupi as a new beta Cephei variable, while the primary is a beta Cephei suspect. A first detailed analysis of line-profile variations of both primary and secondary led to detection of one pulsation frequency near 10.36 c/d in the variability of the secondary, while no clear periodicity was found in the primary, although low-amplitude periodicities are still suspected. The limited accuracy and extent of our dataset did not allow any further analysis, such as mode-identification.

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arXiv2001

The mass of the neutron star in Vela X-1

We measured the radial-velocity curve of HD77581, the B-supergiant companion of the X-ray pulsar Vela X-1, using 183 high-resolution optical spectra obtained in a nine-month campaign. We derive radial-velocity amplitudes for different lines and wavelength regions, and find all are consistent with each other, as well as with values found in previous analyses. We show that one apparent exception, an anomalously low value derived from ultra-violet spectra obtained with the IUE, was due to an error in the analysis procedures. We re-analyse all IUE spectra, and combine the resulting velocities with the ones derived from the new optical spectra presented here, as well as those derived from optical spectra published earlier. As in previous analyses, the radial velocities show strong deviations from those expected for a pure Keplerian orbit. The deviations likely are related to the pronounced line-profile variations seen in our spectra. It turns out that systematic deviations as a function of orbital phase are present. Our best estimate of the radial-velocity amplitude, Kopt = 21.7 +/- 1.6 km/s, has an uncertainty not much reduced to that found in previous analyses, in which the systematic deviations had not been taken into account. Combining our velocity amplitude with the accurate orbital elements of the X-ray pulsar, we infer M_ns sin^3i = 1.78 +/- 0.15 Msun.

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arXiv2000

An Early-Time Infrared and Optical Study of the Type Ia Supernova 1998bu in M96

We present first-season infrared (IR) and optical photometry and spectroscopy of the Type Ia Supernova 1998bu in M96. We also report optical polarimetry of this event. SN1998bu is one of the closest type Ia Supernovae of modern times and the distance of its host galaxy is well-determined. We find that SN1998bu is both photometrically and spectroscopically normal. However, the extinction to this event is unusually high, with Av=1.0 +/-0.11. We find that SN1998bu peaked at an intrinsic Mv=-19.37 +/-0.23. Adopting a distance modulus of 30.25 (Tanvir et al. 1999) and using Phillips et al.'s (1999) relations for the Hubble constant we obtain Ho=70.4 +/-4.3 km/s/Mpc. Combination of our IR photometry with those of Jha et al. (1999) provides one of the most complete early-phase IR light curves for a SN Ia published so far. In particular, SN 1998bu is the first normal SN Ia for which good pre-maximum (in the B band) IR coverage has been obtained. It reveals that the J, H and K light curves peak about 5 days earlier than the flux in the B-band curve.

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arXiv1998

Long- and short-term variability in O-star winds II. Quantitative analysis of DAC behaviour

A quantitative analysis of time series of ultraviolet spectra from a sample of 10 bright O-type stars (cf. Kaper et al. 1996, Paper I) is presented. The migrating discrete absorption components (DACs), responsible for the observed variability in the UV resonance doublets, are modeled. It turns out that the column density of a DAC first increases and subsequently decreases with time when the component is approaching its asymptotic velocity. In some cases this velocity systematically differs from event to event. The recurrence timescale of DACs is derived for most targets, and consistent results are obtained for different spectral lines. The DAC recurrence timescale is interpreted as an integer fraction of the stellar rotation period. In some datasets the variability in the blue edge of the P Cygni lines exhibits a longer period than the DAC variability. This might be related to the systematic difference in asymptotic velocity of successive DACs. The phase diagram for the O giant xi Persei shows clear evidence for so-called ``phase bowing'', which is an observational indication for the presence of curved wind structures like corotating interaction regions. No other O stars in our sample convincingly show phase bowing, but this could be simply due to the absence of periodic signal and hence coherent phase behaviour at low wind velocities.

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arXiv1997

Radio and Optical Follow-up Observations and Improved IPN Position of GRB 970111

We report on Westerbork 840 MHz, 1.4 and 5 GHz radio observations of the improved IPN-WFC error box of the gamma-ray burst GRB 970111, between 26.4 hours and 120 days after the event onset. In the ~ 13 sq arcmin area defined by the IPN (BATSE and Ulysses) annulus and the published refined BeppoSAX Wide Field Camera error box we detected no steady sources brighter than 0.56 mJy (4 sigma), and no varying radio emission, down to 1.0 mJy (4 sigma). We also report on B, V, R and I band observations of the error box with the 4.2 m William Herschel Telescope at La Palma.

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