L. Morales-Rueda

Orbital periods of 22 subdwarf B stars

Subdwarf B (sdB) stars are thought to be core helium burning stars with low mass hydrogen envelopes. In recent years it has become clear that many sdB stars lose their hydrogen through interaction with a binary companion and continue to reside in binary systems today. In this paper we present the results of a programme to measure orbital parameters of binary sdB stars. We determine the orbits of 22 binary sdB stars from 424 radial velocity measurements, raising the sample of sdBs with known orbital parameters to 38. We calculate lower limits for the masses of the companions of the sdB stars which, when combined with the orbital periods of the systems, allow us to discuss approximate evolutionary constraints. We find that a formation path for sdB stars consisting of mass transfer at the tip of the red giant branch (RGB) followed by a common envelope phase explains most, but not all of the observed systems. It is particularly difficult to explain both long period systems and short period, massive systems. We present new measurements of the effective temperature, surface density and surface helium abundance for some of the sdB stars by fitting their blue spectra. We find that two of them (PG 0839 + 399 and KPD 1946 + 4340) do not lie in the extreme horizontal branch (EHB) band, indicating that they are post-EHB stars.

Photometric observations of the Type Ia SN 2002er in UGC 10743

Extensive light and colour curves for the Type Ia supernova SN 2002er are presented as part of the European Supernova Collaboration. We have collected UBV RI photometry from ten different telescopes covering the phases from 7 days before until 619 days after maximum light. Corrections for the different instrumental systems and the nonthermal spectrum of the supernova (S-corrections) have been applied. With the densely sampled light curves we can make detailed comparisons to other well-observed objects. SN 2002er most closely resembles SN 1996X after maximum, but clearly shows a different colour evolution before peak light and a stronger shoulder in V and R bands compared to other well-observed SNe Ia. In particular, the rise time appears to be longer than what is expected from rise-time vs.decline-rate relation. We use several methods to determine the reddening towards SN 2002er based on the colour evolution at near peak and at late phases. The uvoir (bolometric) light curve shows great similarity with SN 1996X, but also indications of a higher luminosity, longer rise time and a more pronounced shoulder 25 days past maximum. The interpretation of the light curves was done with two independent light curve codes. Both find that given the luminosity of SN 2002er the 56 Ni mass exceeds 0.6 M⊙ with prefered values near 0.7 M⊙. Uncertainties in the exact distance to SN 2002er are the most serious limitation of this measurement. The light curve modelling also indicates a high level of mixing of the nickel in the explosion of SN 2002er.

The mass and radius of the M-dwarf in the short-period eclipsing binary RR Caeli

We present new photometry and spectroscopy of the eclipsing white dwarf‐M-dwarf binary star RR Cae. We use timings of the primary eclipse from white-light photo-electric photometry to derive a new ephemeris for the eclipses. We find no evidence for any period change greater than | ˙ P|/P ≈ 5×10 −12 over a time-scale of 10 yr. We have measured the effective temperature of the white dwarf, TWD, from an analysis of two high resolution spectra of RR Cae and find T WD = 7540 K ± 175 K. We estimate a spectral type of M4 for the companion from the same spectra. We have measured the radial velocity of the white dwarf from the Balmer absorption lines and find that the semi-amplitude of the spectroscopic orbit is KWD = 79.3 ± 3.0 km s −1 . We have combined our radial velocity measurements of the M-dwarf with published radial velocities to determine a new spectroscopic orbit for the M-dwarf with a semi-amplitude of KM = 190.2 ± 3.5 km s −1 . We have combined this information with an analysis of the primary eclipse to derive relations between the inclination of the binary and the radii of the two stars. We use cooling models for helium white dwarfs with a wide range of hydrogen layer masses to determine the likely range of the white dwarf radius and, thus, the inclination of the binary and the mass and radius of the M-dwarf. The mass of the M-dwarf is (0.182‐0.183) ± 0.013

A Planetary Nebula around Nova V458 Vulpeculae Undergoing Flash Ionization

Nova V458 Vul erupted on 2007 August 8 and reached a visual magnitude of 8.1 a few days later. Ha images obtained 6 weeks before the outburst as part of the IPHAS Galactic plane survey reveal an 18th magnitude progenitor surrounded by an extended nebula. Subsequent images and spectroscopy of the nebula reveal an inner nebular knot increasing rapidly in brightness due to flash ionization by the nova event. We derive a distance of 13 kpc based on light travel time considerations, which is supported by two other distance estimation methods. The nebula has an ionized mass of 0.2 M-circle dot and a low expansion velocity: this rules it out as ejecta from a, previous nova eruption, and is consistent with it being a similar to 14,000 year old planetary nebula, probably the product of a prior common envelope (CE) phase of evolution of the binary system. The large derived distance means that the mass of the erupting WD component of the binary is high. We identify two possible evolutionary scenarios, in at least one of which the system is massive enough to produce a Type Ia supernova upon merging.

Six detached white-dwarf close binaries

We determine the orbits of four double-degenerate systems (DDs), composed of two white dwarfs and two white-dwarf-M-dwarf binaries. The four DDs, WD1022+050, WD1428+373, WD1824+040 and WD2032+188, show orbital periods of 1.157155(5), 1.15674(2), 6.26602(6) and 5.0846(3) d, respectively. These periods combined with estimates for the masses of the brighter component, based on their effective temperatures, allow us to constrain the masses of the unseen companions. We estimate that the upper limit for the contribution of the unseen companions to the total luminosity in the four DDs ranges between 10 and 20 per cent. In the case of the two white-dwarf-M-dwarf binaries, WD 1042-690 and WD2009+622, we calculate the orbital parameters by fitting simultaneously the absorption line from the white dwarf and the emission core from the M dwarf. Their orbital periods are 0.337083(1) and 0.741 226(2) d, respectively. We find signatures of irradiation on the inner face of the companion to WD2009+622. We calculate the masses of both components from the gravitational redshift and the mass-radius relationship for white dwarfs and find masses of 0.75-0.78 and 0.61-0.64 M ○. for WD 1042-690 and WD2009+622, respectively. This indicates that the stars probably reached the asymptotic giant branch in their evolution before entering a common envelope phase. These two white-dwarf-M-dwarf binaries will become cataclysmic variables, although not within a Hubble time, with orbital periods below the period gap.

The UV-excess survey of the northern galactic plane

The UV-Excess survey of the northern Galactic plane images a 10 ◦ × 185 ◦ wide band, centred on the Galactic equator using the 2.5-m Isaac Newton Telescope in four bands ( U, g, r,He I 5875) down to ∼21-22 mag (∼20 in He I 5875). The setup and data reduction procedures are described. Simulations of the colours of main-sequence stars, giant, supergiants, DA and DB white dwarfs and AM Canum Venaticorum stars are made, including the effects of reddening. A first look at the data of the survey (currently 30 per cent complete) is given.

Cataclysmic variables from a ROSAT/2MASS selection - I. Four new intermediate polars

We report the first results from a new search for cataclysmic variables (CVs) using a combined X-ray (ROSAT)/infrared (2MASS) target selection that discriminates against background active galactic nuclei. Identification spectra were obtained at the Isaac Newton Telescope for a total of 174 targets, leading to the discovery of 12 new CVs. Initially devised to find short-period low-mass-transfer CVs, this selection scheme has been very successful in identifying new intermediate polars. Photometric and spectroscopic follow-up observations identify four of the new CVs as intermediate polars: 1RXS J063631.9+353537 P(orb)similar or equal to 201 min, P-spin= 1008.3408 s or 930.5829 s), 1RXS J070407.9+262501 (P(orb)similar or equal to 250 min, P-spin= 480.708 s) 1RXS J173021.5-055933 (P-orb= 925.27 min, P-spin= 128.0 s), and 1RXS J180340.0+401214 (P-orb= 160.21 min, P-spin= 1520.51 s). RX J1730, also a moderately bright hard X-ray source in the INTEGRAL/IBIS Galactic plane survey, resembles the enigmatic AE Aqr. It is likely that its white dwarf is not rotating at the spin equilibrium period, and the system may represent a short-lived phase in CV evolution.

DISCOVERY OF A CLOSE SUBSTELLAR COMPANION TO THE HOT SUBDWARF STAR HD 149382—THE DECISIVE INFLUENCE OF SUBSTELLAR OBJECTS ON LATE STELLAR EVOLUTION

Substellar objects, like planets and brown dwarfs orbiting stars, are by-products of the star formation process. The evolution of their host stars may have an enormous impact on these small companions. Vice versa a planet might also influence stellar evolution as has recently been argued. Here, we report the discovery of an 8–23 Jupiter-mass substellar object orbiting the hot subdwarf HD 149382 in 2.391 d at a distance of only about five solar radii. Obviously, the companion must have survived engulfment in the red giant envelope. Moreover, the substellar companion has triggered envelope ejection and enabled the sdB star to form. Hot subdwarf stars have been identified as the sources of the unexpected ultraviolet (UV) emission in elliptical galaxies, but the formation of these stars is not fully understood. Being the brightest star of its class, HD 149382 offers the best conditions to detect the substellar companion. Hence, undisclosed substellar companions offer a natural solution for the long-standing formation problem of apparently single hot subdwarf stars. Planets and brown dwarfs may therefore alter the evolution of old stellar populations and may also significantly affect the UV emission of elliptical galaxies.

RX J2130.6+4710 – an eclipsing white dwarf–M-dwarf binary star

We report the detection of eclipses in the close white-dwarf-M-dwarf binary star RX J2130.6+4710. We present light curves in the B, V and I bands and fast photometry obtained with the three-channel CCD photometer Ultracam of the eclipse in the u � , gand rbands. The depth of the eclipse varies from 3.0 mag in the uband to less than 0.1 mag in the I band. The times of mid-eclipse are given by the ephemeris BJD(mid-eclipse) = 2 452 785.681 876(2) + 0.521 035 625(3) E, where figures in parentheses denote uncertainties in the final digit. We present medium-resolution spectroscopy from which we have measured the spectroscopic orbits of the M dwarf and white dwarf. We estimate that the spectral type of the M dwarf is M3.5Ve or M4Ve, although the data on which this is based are not ideal for spectral classification. We have compared the spectra of the white dwarf with synthetic spectra from pure hydrogen model atmospheres to estimate that the effective temperature of the white dwarf is T eff = 18 000 ± 1000 K. We have used the width of the primary eclipse and duration of totality measured precisely from the Ultracam udata combined with the amplitude of the ellipsoidal effect in the I band and the semi-amplitudes of the spectroscopic orbits to derive masses and radii for the M dwarf and white dwarf. The M dwarf has a mass of 0.555 ± 0.023 Mand a radius of 0.534 ± 0.053 R� , which is a typical radius for stars of this mass. The mass of the white dwarf is 0.554 ± 0.017 Mand its radius is 0.0137 ± 0.0014 R� , which is the radius expected for a carbon-oxygen white dwarf of this mass and effective tem- perature. The light curves are affected by frequent flares from the M dwarf and the associated dark spots on its surface can be detected from the distortions to the light curves and radial velocities. RX J2130.6+4710 is a rare example of a pre-cataclysmic variable star that will start mass transfer at a period above the period gap for cataclysmic variables. Ke yw ords: binaries: close - binaries: eclipsing - stars: fundamental parameters - stars: individual: RX J2130.6+4710 - white dwarfs.

Rotational period of WD 1953 — 011 — a magnetic white dwarf with a star-spot

WD 1953-011 is an isolated, cool (7920 +/- 200K) magnetic white dwarf (MWD) with a low average field strength (~70kG), and a higher than average mass (~0.74M solar ). Spectroscopic observations taken by Maxted et al. showed variations of equivalent width in the Balmer lines, unusual in a low-field white dwarf. Here we present V-band photometry of WD 1953-011 taken at seven epochs over a total of 22 months. All of the data sets show a sinusoidal variation of approximately 2 per cent peak-to-peak amplitude. We propose that these variations are due to a star-spot on the MWD, analogous to a sunspot, which is affecting the temperature at the surface, and therefore its photometric magnitude. The variations have a best-fitting period over the entire 22 months of 1.4418 d, which we interpret as the rotational period of the white dwarf.