R. Costero

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.

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.

Optical variability of the Seyfert nucleus NGC 7469 in timescales from days to minutes

We report optical photometric observations of the Seyfert nucleus NGC 7469. During the first observing run in 1989, night-to-night measurements were done during 13 photometric nights spanning November 3-30. The largest variation, Δm=0 m .403, within a 20 arcsec diaphragm, occurred in eleven days and a decrease in brightness of Δm=0 m .337 (∼70% of the luminosity of the unresolved nuclear component) occurred in only five days. During the second run in August 1990, all-night monitoring was done during five photometric nights (∼29 hr) using differential photometry techniques

G 112-29 (=NLTT 18149): A VERY WIDE COMPANION TO GJ 282 AB WITH A COMMON PROPER MOTION, COMMON PARALLAX, COMMON RADIAL VELOCITY, AND COMMON AGE

We have made a search for common proper motion (CPM) companions to the wide binaries in the solar vicinity. We found that the binary GJ 282AB has a very distant CPM companion (NLTT 18149) at a separation

Determination of the basic parameters of the dwarf nova EY Cygni

s=1.09 \arcdeg

San Pedro Mártir: astronomical site evaluation

. Improved spectral types and radial velocities are obtained, and ages determined for the three components. The Hipparcos trigonometric parallaxes and the new radial velocities and ages turn out to be very similar for the three stars, and provide strong evidence that they form a physical system. At a projected separation of 55733AU from GJ 282AB, NLTT 18149 ranks among the widest physical companions known.

KINEMATICS OF THE ORION TRAPEZIUM BASED ON DIFFRACTO-ASTROMETRY AND HISTORICAL DATA

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� .

Dual infrared camera for near and mid infrared observations

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.

Did EY Cyg go through a Nova explosion

Using the novel Diffracto-Astrometry technique, we analyze 44 Hubble Space Telescope Wide Field Planetary Camera 2 images of the Orion Trapezium (OT) taken over a span of 12?yr (1995-2007). We measure the relative positions of the six brighter OT components (A-F) and supplement these results with measurements of the relative separations and position angles taken from the literature, thus extending our analysis time base to ~200 yr. For every pair of components we find the relative rate of separation as well as the temporal rate of change of their position angles, which enable us to determine the relative kinematics of the system. Component E shows a velocity larger than the OTs escape velocity, thus confirming that it is escaping from the gravitational pull of this system.