Oscillations in Arcturus from WIRE photometry

Observations of the red giant Arcturus (Alpha Boo) obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a baseline of 19 successive days in 2000 July-August are analysed. The amplitude spectrum has a significant excess of power at low-frequencies. The highest peak is at about 4.1 micro-Hz (2.8 d), which is in agreement with previous ground-based radial velocity studies. The variability of Arcturus can be explained by sound waves, but it is not clear whether these are coherent p-mode oscillations or a single mode with a short life-time.Comment: 6 pages, 1 Latex file, 4 .eps figures, 2 .sty files, ApJL, 591, L151 See erratum (astro-ph/0308424

One-dimensional behavior of elongated Bose-Einstein condensates

We study the properties of elongated Bose-Einstein condensates. First, we show that the dimensions of the condensate after expansion differs from the 3D Thomas-Fermi regime. We also study the coherence length of such elongated condensates.Comment: proceeding of Quantum Gases in Low Dimension, Les Houches 2003, 8 pages, 5 figure

The Detection of a 3.5-h Period in the Classical Nova Velorum 1999 (V382 Vel) and the Long Term Behavior of the Nova Light Curve

We present CCD photometry, light curve and time series analysis of the classical nova V382 Vel (N Vel 1999). The source was observed for 2 nights in 2000, 21 nights in 2001 and 7 nights in 2002 using clear filters. We report the detection of a distinct period in the light curve of the nova P=0.146126(18) d (3.5 h). The period is evident in all data sets, and we interpret it as the binary period of the system. We also measured an increase in the amplitude modulation of the optical light (in magnitude) by more than 55% from 2000 to 2001 and about 64% from 2001 to 2002. The pulse profiles in 2001 show deviations from a pure sinusoidal shape which progressively become more sinusoidal by 2002. The main cause of the variations in 2001 and 2002 can be explained with the occultation of the accretion disk by the secondary star. We interpret the observed deviations from a pure sinusoidal shape as additional flux resulting from the aspect variations of the irradiated face of the secondary star.Comment: 16 pages and 4 figures, accepted as it stands to be published in the Astronomical Journal (AJ

Detection of orbital and superhump periods in Nova V2574 Ophiuchi (2004)

We present the results of 37 nights of CCD unfiltered photometry of nova V2574 Oph (2004) from 2004 and 2005. We find two periods of 0.14164 d (~3.40 h) and 0.14773 d (~3.55 h) in the 2005 data. The 2004 data show variability on a similar timescale, but no coherent periodicity was found. We suggest that the longer periodicity is the orbital period of the underlying binary system and that the shorter period represents a negative superhump. The 3.40 h period is about 4% shorter than the orbital period and obeys the relation between superhump period deficit and binary period. The detection of superhumps in the light curve is evidence of the presence of a precessing accretion disk in this binary system shortly after the nova outburst. From the maximum magnitude - rate of decline relation, we estimate the decay rate t_2 = 17+/-4 d and a maximum absolute visual magnitude of M_Vmax = -7.7+/-1.7 mag.Comment: 6 pages, 6 figures, 2 .sty files, AJ accepted, minor change to one of reference

A photometric study of the newly discovered eclipsing cataclysmic variable SDSS J040714.78-064425.1

We present the results obtained from unfiltered photometric CCD observations of the newly discovered cataclysmic variable SDSS J040714.78-064425.1 made during 7 nights in November 2003. We establish the dwarf nova nature of the object as it was in outburst during our observations. We also confirm the presence of deep eclipses with a period of 0.17017d+/-0.00003 in the optical light curve of the star. In addition, we found periods of 0.166d+/-0.001 and possibly also 5.3d+/-0.7 in the data. The 0.17017d periodicity is consistent within the errors with the proposed orbital period of 0.165d (Szkody et. al. 2003) and 0.1700d (Monard 2004). Using the known relation between the orbital and superhump periods, we interpret the 0.166d and 5.3d periods as the negative superhump and the nodal precession period respectively. SDSS J040714.78-064425.1 is then classified as a negative superhump system with one of the largest orbital periods.Comment: 6 pages, 8 figures. accepted by PAS

Discovery of Irradiation Induced Variations in the Light Curve of the Classical Nova Cygni 2001 No.2 (V2275 Cyg)

We present the CCD photometry, light curve and time series analysis of the classical nova V2275 Cyg (N Cyg 2001 No.2). The source was observed for 14 nights in total using an R filter in 2002 and 2003 with the 1.5 m Russian-Turkish joint telescope (RTT150) at the TUBITAK (The Scientific and Technical Research Council of Turkey) National Observatory in Antalya Turkey, as part of a large program on the CCD photometry of Cataclysmic Variables (CVs). We report the detection of two distinct periodicities in the light curve of the nova : a) P_1=0.31449(15) d -- 7.6 h, b) P_2=0.017079(17) d -- 24.6 min. The first period is evident in both 2002 and 2003 whereas the second period is only detected in the 2003 data set. We interpret the first period as the orbital period of the system and attribute the orbital variations to aspect changes of the secondary irradiated by the hot WD. We suggest that the nova was a Super Soft X-ray source in 2002 and, perhaps, in 2003. The second period could be a QPO originating from the oscillation of the ionization front (due to a hot WD) below the inner Lagrange point as predicted by King (1989) or a beat frequency in the system as a result of the magnetic nature of the WD if steady accretion has already been re-established.Comment: 6 pages and 8 figures. Accepted to be published in MNRAS main Journal as it stand

SDSS J210014.12+004446.0: A New Dwarf Nova with Quiescent Superhumps?

We report follow-up observations of the Sloan Digital Sky Survey Cataclysmic Variable SDSS J210014.12+004446.0 (hereafter SDSS J2100). We obtained photometry and spectroscopy in both outburst and quiescent states, providing the first quiescent spectrum of this source. In both states, non-sinusoidal photometric modulations are apparent, suggestive of superhumps, placing SDSS J2100 in the SU UMa subclass of dwarf novae. However, the periods during outburst and quiescence differ significantly, being 2.099 plus or minus 0.002 hr and 1.96 plus or minus 0.02 hr respectively. Our phase-resolved spectroscopy during outburst yielded an estimate of about 2 hr for the orbital period, consistent with the photometry. The presence of the shorter period modulation at quiescence is unusual, but not unique. Another atypical feature is the relative weakness of the Balmer emission lines in quiescence. Overall, we find a close similarity between SDSS J2100 and the well-studied superhump cataclysmic Variable V503 Cygni. By analogy, we suggest that the quiescent modulation is due to a tilted accretion disk -- producing negative superhumps -- and the modulation in outburst is due to positive superhumps from the precession of an elliptical disk.Comment: 6 pages, 5 eps figures, accepted by PASP Dec. 16th, 200

Nova V4743 Sagittarii 2002: An Intermediate Polar Candidate

We present the results of 11 nights of CCD unfiltered photometry of V4743 Sgr (Nova Sgr 2002 # 3) from 2003 and 2005. We find two periods of 0.2799 d ~ 6.7 h and 0.01642 d ~ 24 min in the 2005 data. The long period is also present in the 2003 data, but only weak evidence of the shorter period is found in this year. The 24-min period is somewhat longer than the 22-min period, which was detected from X-ray observations. We suggest that the 6.7-h periodicity represents the orbital period of the underlying binary system and that the 24-min period is the beat periodicity between the orbital period and the X-ray period, which is presumably the spin period of the white dwarf. Thus, V4743 Sgr should be classified as an intermediate polar (DQ Her star). About six months after the nova outburst, the optical light curve of V4743 Sgr seemed to show quasi-periodic oscillations, which are typical of the transient phase in classical nova. Therefore, our results support the previous suggestion that the trans ition phase in novae may be related to intermediate polars.Comment: 7 pages, 6 figures, AJ accepte

Solar-like oscillations in the metal-poor subgiant nu Indi: II. Acoustic spectrum and mode lifetime

Convection in stars excites resonant acoustic waves which depend on the sound speed inside the star, which in turn depends on properties of the stellar interior. Therefore, asteroseismology is an unrivaled method to probe the internal structure of a star. We made a seismic study of the metal-poor subgiant star nu Indi with the goal of constraining its interior structure. Our study is based on a time series of 1201 radial velocity measurements spread over 14 nights obtained from two sites, Siding Spring Observatory in Australia and ESO La Silla Observatory in Chile. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 200 and 500 uHz showing regularity with a large and small spacing of 25.14 +- 0.09 uHz and 2.96 +- 0.22 uHz at 330 uHz. Thirteen individual modes have been identified with amplitudes in the range 53 to 173 cm/s. The mode damping time is estimated to be about 16 days (1-sigma range between 9 and 50 days), substantially longer than in other stars like the Sun, the alpha Cen system or the giant xi Hya.Comment: 5 pages, 7 figures, A&A accepte