J. Echevarría

Multisite spectroscopic seismic study of the β Cep star V2052 Ophiuchi: inhibition of mixing by its magnetic field

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f1 = 7.148 46 d−1) and by rotational modulation (Prot = 3.638 833 d). Two non-radial low-amplitude modes (f2 = 7.756 03 d−1 and f3 = 6.823 08 d−1) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign and known in the literature. Using the photometric constraints on the degrees l of the pulsation modes, we show that both f2 and f3 are prograde modes with (l, m) = (4, 2) or (4, 3). These results allowed us to deduce ranges for the mass (M ∈ [8.2, 9.6] M⊙) and central hydrogen abundance (Xc ∈ [0.25, 0.32]) of V2052 Oph, to identify the radial orders n1 = 1, n2 = −3 and n3 = −2, and to derive an equatorial rotation velocity veq ∈ [71, 75] km s−1. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (αov ∈ [0, 0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic β Cep star θ Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior.

Cyclic brightening in the short-period WZ Sge-type cataclysmic variable SDSS J080434.20+510349.2

Aims. We observed a new cataclysmic variable (CV) SDSS J080434.20+510349.2 to study the origin of long-term variability found in its light curve. Methods. Multi-longitude, time-resolved, photometric observations were acquired to analyze this uncommon behavior, which has been found in two newly discovered CVs. Results. This study of SDSS J080434.20+510349.2 concerns primarily the understanding of the nature of the observed, doublehumped, light curve and its relation to a cyclic brightening that occurs during quiescence. The observations were obtained early in 2007, when the object was at about V ∼ 17.1, about 0.4 mag brighter than the pre-outburst magnitude. The light curve shows a sinusoidal variability with an amplitude of about 0.07 mag and a periodicity of 42.48 min, which is half of the orbital period of the system. We observed in addition two “mini-outbursts” of the system of up to 0.6 mag, which have a duration of about 4 days each. The “mini-outburst” has a symmetric profile and is repeated in approximately every 32 days. Subsequent monitoring of the system shows a cyclical behavior of such “mini-outbursts” with a similar recurrence period. The origin of the double-humped light curve and the periodic brightening is discussed in the light of the evolutionary state of SDSS J080434.20+510349.2.

U Geminorum: A Test Case for Orbital Parameter Determination

High-resolution spectroscopy of U Gem was obtained during quiescence. We did not find a hot spot or gas stream around the outer boundaries of the accretion disk. Instead, we detected a strong narrow emission region near the location of the secondary star. We measured the radial velocity curve from the wings of the double-peaked Hα emission line and obtained a semiamplitude value that is in excellent agreement with that obtained from observations in the ultraviolet spectral region by Sion et al. We also present a new method to obtain K2, which enhances the detection of absorption or emission features arising in the late-type companion. Our results are compared with published values derived from the near-infrared Na I line doublet. From a comparison of the TiO band with those of late-type M stars, we find that a best fit is obtained for an M6 V star, contributing 5% of the total light at that spectral region. Assuming that the radial velocity semiamplitudes accurately reflect the motion of the binary components, then from our results Kem = 107 ± 2 km s-1 and Kabs = 310 ± 5 km s-1; using the inclination angle given by Zhang & Robinson, i = 69.7° ± 0.7°, the system parameters become MWD = 1.20 ± 0.05 M⊙, MRD = 0.42 ± 0.04 M⊙, and a = 1.55 ± 0.02 R⊙. Based on the separation of the double emission peaks, we calculate an outer disk radius of Rout/a ~ 0.61, close to the distance of the inner Lagrangian point L1/a ~ 0.63. Therefore, we suggest that, at the time of observations, the accretion disk was filling the Roche lobe of the primary and the matter leaving the L1 point was colliding with the disk directly, producing the hot spot at this location.

High-dispersion absorption-line spectroscopy of AE Aqr

High-dispersion time-resolved spectroscopy of the unique magnetic cataclysmic variable AE Aqr is presented. A radial velocity analysis of the absorption lines yields K2 = 168.7 ± 1 km/s. Substantial deviations of the radial velocity curve from a sinusoid are interpreted in terms of intensity variations over the secondary star’s surface. A complex rotational velocity curve as a function of orbital phase is detected which has a modulation frequency of twice the orbital frequency, leading to an estimate of the binary inclination angle that is close to 70◦. The minimum and maximum rotational velocities are used to indirectly derive a mass ratio of q = 0.6 and a radial velocity semi-amplitude of the white dwarf of K1 = 101 ± 3 km/s. We present an atmospheric temperature indicator, based on the absorption-line ratio of Fe I and Cr I lines, whose variation indicates that the secondary star varies from K0 to K4 as a function of orbital phase. The ephemeris of the system has been revised, using more than 1000 radial velocity measurements, published over nearly five decades. From the derived radial velocity semi-amplitudes and the estimated inclination angle, we calculate that the masses of the stars are M1 = 0.63±0.05 Msun, M2 = 0.37±0.04 Msun, and their separation is a = 2.33±0.02 Rsun. Our analysis indicates the presence of a late-type star whose radius is larger, by a factor of nearly 2, than the radius of a normal main-sequence star of the same mass. Finally, we discuss the possibility that the measured variations in the rotational velocity, temperature and spectral type of the secondary star as functions of orbital phase may, like the radial velocity variations, be attributable to regions of enhanced absorption on the star’s surface.

Determination of the basic parameters of the dwarf nova EY Cygni

Context. High-dispersion spectroscopy of EY Cyg obtained from data spanning twelve years show, for the first time, the radial velocity curves from both emission and absorption line systems, yielding semi-amplitudes Kem = 24 ± 4k m s −1 and Kabs = 54 ± 2k m s −1 . The orbital period of this system is found to be 0.4593249(1) d. The masses of the stars, their mass ratio and their separation are found to be M1 sin 3 i = 0.015 ± 0.002 M� , M2 sin 3 i = 0.007 ± 0.002 M� , q = K1/K2 = M2/M1 = 0.44 ± 0.02 and a sini = 0.71 ± 0.04 R� . We also found that the spectral type of the secondary star is around K0, consistent with an early determination by Kraft (1962). Aims. From the spectral type of the secondary star and simple comparisons with single main sequence stars, we conclude that the radius of the secondary star is about 30 per cent larger than a main sequence star of the same mass. Methods. We also present VRI CCD photometric observations, some of them simultaneous with the spectroscopic runs. The photometric data shows several light modulations, including a sinusoidal behaviour with twice the frequency of the orbital period, characteristic of the modulation coming from an elongated, irradiated secondary star. Low and high states during quiescence are also detected and discussed. Results. From several constrains, we obtain tight limits for the inclination angle of the binary system between 13 and 15 degrees, with a best value of 14 degrees obtained from the sinusoidal light curve analysis. Conclusions. From the above results we derive masses M1 = 1.10 ± 0.09 M� , M2 = 0.49 ± 0.09 M� , and a binary separation a = 2.9 ± 0.1 R� .

The kinematics of the most oxygen-poor planetary nebula PN G 135.9+55.9

PN G 135.9+55.9 is a compact, high excitation nebula that has been identified recently as the most oxygen-poor halo planetary nebula. Given its very peculiar characteristics and potential implications in the realms of stellar and Galactic evolution, additional data are needed to firmly establish its true nature and evolutionary history. Here we present the first long- slit, high spectral resolution observations of this object in the lines of H and Heii4686. The position-velocity data are shown to be compatible with the interpretation of PN G 135.9+55.9 being a halo planetary nebula. In both emission lines, we find the same two velocity components that characterize the kinematics as that of an expanding elliptical envelope. The kinematics is consistent with a prolate ellipsoidal model with axis ratio about 2:1, a radially decreasing emissivity distribution, a velocity distribution that is radial, and an expansion velocity of 30 km s 1 for the bulk of the material. To fit the observed line profiles, this model requires an asymmetric matter distribution, with the blue-shifted emission considerably stronger than the red-shifted emission. We find that the widths of the two velocity components are substantially wider than those expected due to thermal motions, but kinematic structure in the projected area covered by the slit appears to be sucient to explain the line widths. The present data also rule out the possible presence of an accretion disk in the system that could have been responsible for a fraction of the H flux, further supporting the planetary nebula nature of PN G 135.9+55.9.

San Pedro Mártir: astronomical site evaluation

The Observatorio Astronomico Nacional at San Pedro Martir is situated on the summit of the San Pedro Martir Sierra in the Baja California peninsula of Mexico, at 2800m above sea level. For as long as three decades, a number of groups and individuals have gathered extremely valuable data leading to the site characterization for astronomical observations. Here we present a summary of the most important results obtained so far. The aspects covered are: weather, cloud coverage, local meteorology, atmospheric optical extinction, millimetric opacity, geotechnical studies, seeing, optical turbulence profiles, wind profiles and 3D simulations of atmospheric turbulence. The results place San Pedro Martir among the most favorable sites in the world for astronomical observations. It seems to be particularly well-suited for extremely large telescopes because of the excellent turbulence and local wind conditions, to mention but two characteristics. Long-term monitoring of some parameters still have to be undertaken. The National University of Mexico (UNAM) and other international institutions are putting a considerable effort in that sense.

The orbital period of intermediate polar 1WGA J1958.2+3232

The detection of the orbital period of

Multiwavelength observations of V479 Andromedae: a close compact binary with an identity crisis

4\fh36

Photometry of the eclipsing cataclysmic variable SDSS J152419.33+220920.0

is reported for the new Intermediate Polar 1 WGA J1958.2+3232. The orbital period was derived from time-resolved photometric and spectral observations. We also confirmed the 733 s spin period of the White Dwarf consistent with the X-ray pulsations and were able to distinguish the beat period in the light curve. Strong modulations with orbital period are detected in the emission lines from spectral observations. They show the presence of a bright hot spot on the edge of the accretion disk. The parameters of this recently discovered Intermediate Polar are determined.