Radial velocity variations of the pulsating subdwarf B star PG 1605+072

We present an analysis of high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Periodic radial motions are detected at frequencies similar to those reported for photometric variations in the star, with amplitudes of up to 6 km s⁻¹. Differences between relative strengths for given frequency peaks for our velocity data and previously measured photometry are probably a result of shifting of power between modes over time. Small differences in the detected frequencies may also indicate mode-shifting. We report the detection of line-shape variations using the moments of the cross-correlation function profiles. It may be possible to use the moments to identify the pulsation modes of the star.     

Haro’s star (PG 1444+236): A hot subdwarf of the Galactic halo?

We present our photometric and spectroscopic observations of the hot emission-line high-latitude (b=+64°) star discovered by Haro. The star exhibited no light variability during 1993–2001. Based on our observations and on the detailed study of the star by Herbig (1992), we improved its parameters, T=22000 K and logg=4.2, and inferred its evolutionary status. We show that Haro’s star does not belong to the class of protoplanetary objects but is most likely a hot subdwarf of the Galactic halo with an emission-line spectrum formed in the outer layers of the star or in its stellar wind.     

Resolving the pulsations of the subdwarf B star KPD 2109 + 4401

We present the results of extensive time-series photometry of the pulsating subdwarf B star KPD 2109 + 4401. Our data set consists of 29 data runs with a total length of 182.6 h over 31 d, collected at five observatories in 2004. These data comprised high signal-to-noise ratio observations acquired with larger telescopes and wider time-coverage observations obtained with smaller telescopes. They are sufficient to resolve the pulsation structure to 0.4 μHz and are the most extensive data set for this star to date. With these data, we identify eight pulsation frequencies extending from 4701 to 5481 μHz, corresponding to periods of 182–213 s. The pulsation frequencies and their amplitudes are examined over several time-scales with some frequencies showing amplitude variability.     

MSST observations of the pulsating sdB star PG 1605+072

We present the first results from the MultiSite Spectroscopic Telescope (MSST) observations of the sdBV star PG 1605+072. Pulsating sdB stars (also known as EC 14026 stars) offer the chance to gain new insights into the formation and evolution of extreme Horizontal Branch stars using the tools of asteroseismology. PG 1605+072 is an outstanding object in its class, with the richest frequency spectrum, the longest periods, and the largest variations. The MSST campaign took place in May/June 2002 immediately following the Whole Earth Telescope Xcov22 run, which observed PG 1605+072 as an alternate target. We will first give an overview of the project and its feasibility, after which we will present the massive data set, made up of 399 h of photometry and 151 h of spectroscopy. The overall aims of the project are to examine light/velocity amplitude ratios and phase differences, changes in equivalent width/line index, and λ-dependence of photometric amplitudes, and to use these properties for mode identification.     

Resolving the pulsations of subdwarf B stars: PG 0154+182, HS 1824+5745 and HS 2151+0857

We continue our programme of extended single-site observations of pulsating subdwarf B (sdB) stars and present the results of extensive time-series photometry to resolve the pulsation spectra for use in asteroseismological analyses. PG 0154+182, HS 1824+5745 and HS2151+0857 were observed at the MDM Observatory during 2004 and 2005. Our observations are sufficient to resolve the pulsations of all three target stars. We extend the number of known frequencies for PG 0154+182 from one to six, confirm that HS 1824+5745 is a monoperiodic pulsator and extend the number of known frequencies to five for HS 2151+0857. We perform standard tests to search for multiplet structure, measure amplitude variations as pertains to stochastic excitation and examine the mode density to constrain the mode degree ℓ.     

Preliminary results of the multisite time-series campaign on the sdB pulsator PG 1325+101

I present a model for the formation and evolution of a massive disk galaxy, within a growing dark halo whose mass evolves according to cosmological simulations of structure formation. The galactic evolution is simulated with a new 3D chemo-dynamical code, including dark matter, stars and a multi-phase ISM. We follow the evolution from redshift z = 4.85 until the present epoch. The energy release by massive stars and supernovae prevents a rapid collapse of the baryonic matter and delays the maximum star formation until redshift z ≈ 1. The galaxy forms radially from inside-out and vertically from top-to-bottom. The feedback of stars leads to turbulent motions and large-scale flows in the ISM. As one result the galactic disk is significantly enriched by chemical elements synthesized in bulge stars.     

Radial velocity and line-profile variations in the sdBV star PG 1325+101

Historically, any newly discovered object needed to be “confirmed” with optical observations. Catalogs were published, such as the PKS (Parkes Catalog), with stamp-sized photographs that allowed us to “see” what was just found. This is still somewhat true, although far less than in the past. We are probably reaching an information overload with more efficient instruments, larger detectors, multiple wavelength coverage and an increasing number of ground and space-based facilities. At the same time, information technology is catching up and is allowing us to use the data regardless of where they reside. An increasing need of multi-wavelength observations to understand the underlying physics of the observed phenomena and the challenge to mine petabyte databases is leading to a federation of archives and cooperation among computer scientists and astronomers. These are the seeds of a virtual observatory, a cyberspace entity where the data are ready to be found and analyzed. In the United States, the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA) are funding initiatives that will lead to the creation of this entity. This paper describes these projects.     

Radial velocity study of the pulsating subdwarf B star and possible Type Ia supernova progenitor KPD 1930+2752

We report the results of a high-time-resolution radial velocity study of the subdwarf B star and possible Type Ia supernova progenitor KPD 1930+2752. There were no significant peaks in the power spectrum of the velocity curve above our detection limit, about 4 km s⁻¹, at the frequencies where peaks arising from pulsation were present in the photometric data of previous researchers. We report an orbital velocity amplitude,  348.5±1 km s^-1  , in agreement with that reported by previous investigators. We find an orbital period of   P =0.095 093 08±0.000 000 15 d  based on our data and the ephemeris of Maxted et al.     

Time-resolved high-resolution spectroscopy of the pulsating sdB star QQ Vir (PG1325+101)

In this work, a standard solar model is computed with new reaction rates that take into account the exact astrophysical S-factor, S _e for the ³He(³He,2p)⁴He, ³He(α,γ)⁷Be and ⁷Be(p,γ)⁸B reactions. The exact S-factor which is valid for all energies is an improved version of the S-factor in the lower-energy approximation (Yusof and Kassim in Astrophys. Space Sci., 2009b). The effects of these new nuclear reaction rates on the solar neutrino fluxes are then discussed by comparing this model to a solar model computed with the standard NACRE reaction rates (Angulo et al. in Nucl. Phys. A. 656:3, 1999). The new reaction rates are found to decrease the neutrinos flux for ⁷Be and ⁸B by about 6% and 16%, respectively. A solar model is also computed with the reaction rates of the LUNA collaboration for ¹⁴N(p,γ)¹⁵O (Formicola et al. in Phys. Lett. B 591:61, 2004). In this case, a clear decrease of the fluxes for ¹³N and ¹⁵O is observed to be in good agreement with previous results (see e.g. Bahcall et al. in Astrophys. J. 621:L88, 2005).     

A new red variable star in the globularcluster M4

G302 = L3107 is a red star located at the lowest end of the red giant branch of the globular cluster M4. According to its location on the C-M diagram, G302 may be a cluster member. No proper motion or radial velocity determinations are available up to date.

We discovered that C302 is a new variable star with a main period of 1.24719 day and a peak to peak amplitude of about 0.3 mag in V. It may have a second period of 2.38249 day with an amplitude of about 0.05 mag. If it is a cluster member, then there will be interesting implications for the the theory of stellar evolution.     

The photometric periods of the nova-like cataclysmic variable LQ Pegasi (PG 2133+115)

We present a time-resolved differential photometric study and time series analysis of the nova-like cataclysmic variable star LQ Peg. We discover three periodicities in the photometry, one with a period of 3.42 ± 0.03 h, and another with a period of 56.8 ± 0.01 h. We interpret these to be the apsidal superhump and precessional periods of the accretion disk, respectively, and predict that the orbital period of LQ Peg is 3.22 ± 0.03 h. The third periodicity, with a period of 41.3 ± 0.01 h, we interpret to be the nodal precessional period of the accretion disk. We also report a flare that lasted four minutes and had an energy in visible light of (1.2 ± 0.3) × 10³⁶ ergs, or 10^4-5 times more energetic than the largest solar flares, comparable to the most energetic visible-light stellar flares known. We calculate the absolute magnitude of LQ Peg to be M_J = 4.78 ± 0.54, and its distance to be 800 ± 200 pc.     

Detection of superhumps in the cataclysmic variable V378 Peg (PG 2337+300)

The cataclysmic variable V378 Peg is known since 15 years. Although V378 Peg is a rather bright star (14 mag), it underwent no detailed study. We performed photometric observations of V378 Peg during 75 h with the goal to detect periodic brightness variations. The obtained light-curves clearly showed changes with a period of about 3 h. The Fourier analysis reveals that this oscillation occurs with a period of 3.238 h and a semiamplitude of 0.07 mag. Although the detected oscillation possesses certain coherence, it appears to have a slightly unstable period or phase. Therefore, the detected period cannot be the orbital period of the V378 Peg system. Because such instability is typical of superhumps, we must consider the detected oscillation as superhumps. Furthermore, V378 Peg shows no outbursts and has to be a nova-like variable rather than a dwarf nova. Hence, the detected superhumps have to be regarded as permanent superhumps. Because superhump periods in cataclysmic variables are close to orbital periods, we can find the place of V378 Peg in the orbital period distribution of cataclysmic variables. V378 Peg is a permanent superhump system above the upper edge of the 2-3 h period gap in the orbital period distribution.     

Variability of the period of the star DU Monocerotis,an RR Lyrae variable with the Blazhko effect

In 2012–2014 we obtained 3641 CCD frames of the fields of the RR Lyrae (AB subtype, P = 0.583 days) variable DU Mon with BV I _c filters using the 76-cm telescope of the South African Astronomical Observatory (SAAO) and the 1-m telescopes of the Las Cumbres Observatory Global Telescope Network (LCOGT). Our observations confirmed the presence of the Blazhko effect that we suspected previously and allowed its period to be determined, \({P_{Bl}} = 60_ \cdot ^d52 \pm 0_ \cdot ^d03\). Using all of the available observations, we constructed an O–C diagram spanning a time interval of 86 years that revealed at least one abrupt change in the pulsation period (a decrease by 15.26 s).