Maria J. Lopez-Gonzalez

Spectral airglow temperature imager (SATI): a ground-based instrument for the monitoring of mesosphere temperature

The spectral airglow temperature imager is a two-channel, Fabry-Perot spectrometer with an annular field of view and a cooled CCD detector. The detected fringe pattern contains spectral information in the radial direction and azimuthal spatial information from the annular field of view. The instrument measures the rotational temperature from the O2 atmospheric (0,1) nightglow emission layer at 94 km and from the Q branch of the OH Meinel (6,2) band emission layer at 87 km. The method for temperature derivation is based on the temperature dependence of the line-emission rates. This dependence allows a determination of the temperature by a least-squares fit of the measured spectrum to a set of synthetic spectra, an approach that minimizes the effect of noise from the sky background and the detector. The spectral airglow temperature imager was developed to meet a need for monitoring the role of the mesosphere in climate variability through long-term observation of the mean temperature and the gravity waves from a single station, as well as large-scale wave perturbations through the use of multiple stations.

SATI: A SPECTRAL AIRGLOW TEMPERATURE IMAGER

Abstract An empirical understanding of planetary scale perturbations in the upper atmosphere is most effectively gained by the complementary use of both satellite and ground-based instrumentation. Limb observations from space provide vertical information and broad global coverage, while ground-based observations provide detailed system development in both solar and universal time. Ground-based instruments must be stable, accessible to but not dependent upon operator interaction, and inexpensive. The technique of interference filter spectral scanning has shown itself to satisfy these requirements when embodied in the instrument MORTI, a mesopause oxygen rotational temperature imager. MORTI has been especially useful in studies of fluctuations of the temperature and emission rate of the O2 Atmospheric airglow layer. SATI represents a complete redesign of the MORTI concept in order to make it an even better instrument for ground-based networks. The major new features are the replacement of cryogenic by thermo-electric cooling, real time temperature and emission rate readout, remote operation, and the addition of an OH channel. Examples of spectral airglow images taken with SATI are presented and its potential use in the COSTEP PSMOS project (planetary scale mesopause observing system) is discussed.

The frequency ratio method and the new multiperiodic gamma Doradus star HD 218427

Oscillations of γ Dor-type were discovered in the star HD 218427 through simultaneous uvby photometric observations carried out in the year 2003. A few Hβ-Crawford measurements were also collected for calibration purposes and they locate this star well inside the γ Dor instability region. We find HD 218427 to be deficient in metals, similar to other well-defined γ Dor stars, and discuss the possibility that it has a λ Boo nature. We carried out frequency analysis for different filters, including the combined “vby” filter, and five frequencies were found as significant with periods ranging between 0.3 and 0.8 days. The recently-developed frequency ratio method is used in order to identify the excited modes. The results are consistent with an l = 2 identification for all the modes and with high radial quantum numbers (n ∼ 40) for the three main observed periodicities. The possibility of multiplet structures is also discussed. However, no consistency is found when using the time-dependent convection treatment to discriminate modes. This disagreement can be due to the large rotation velocity taking place in HD 218427 and, consequently, the significant coupling between the modes.

The field high-amplitude SX Phoenicis variable BL Camelopardalis: results from a multisite photometric campaign. I. Pulsation

Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims. An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods. The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005–2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes. Results. The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 significant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f0 = 25.5765 cd −1 (∆V = 153 mmag) and the other 21 are excited modes showing very small amplitudes. Some additional periodicities are probably still remaining in the residuals. This represents the most complex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are confirmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f0 seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is confirmed, while the secondary peak f1 = 25.2523 cd −1 is identified as a nonradial mixed mode g4 with � = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not confirmed. Nevertheless, the frequency f6 = 32.6464 cd −1 could correspond to the first radial overtone.

Simultaneous uvby photometry of the

We present the results of a three-year Stromgren uvby photometric study of the recently discovered multiperiodic low amplitude Sct-type pulsator HD 129231. Some additional H-Crawford measurements were also collected. Multiperiodicity is needed to describe the pulsational behaviour of this variable during each of the observing runs. A set of ve signicant frequencies has been found as the best tting for the 1997 dataset, but only the two main ones result as signicant during the 1995 and 1996 observing runs. Amplitude variations from season to season are also found for the main frequency f1. Nonradial pulsation is suggested for some of the modes. Using the derived uvby indices, the most relevant physical parameters of HD 129231 are also determined placing this object as a hot Population I Sct star evolving on its main sequence stage.

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We present the results of a multi-site photometric campaign carried out in 2004–2008 for the Algol-type eclipsing binary system CT Her, the primary component of which displays δ Scuti-type oscillations. Our data consist of differential light curves collected in the filters B and V, which were analysed using the method of Wilson-Devinney (Phoebe). After identifying an adequate binary model and removing the best-fit light-curve solution, we performed a Fourier analysis of the residual B and V light curves to investigate the pulsational behaviour. We confirm the presence of rapid pulsations with a main period of 27.2 min. Up to eight significant frequencies with semi-amplitudes in the range 3 to 1 mmag were detected, all of which lie in the frequency range 43.5–53.5 d −1 . This result is independent of the choice of the primary’s effective temperature (8200 or 8700 K) since the light-curve models of the binary are very similar in both cases. This is yet another case of a complex frequency spectrum observed for an accreting δ Scuti-type star (after Y Cam). In addition, we demonstrate that the amplitudes of several pulsation frequencies provide evidence of variability on timescales as short as 1–2 years, perhaps even less. Moreover, our analysis takes into account some recently acquired spectra, from which we obtained the corresponding radial velocities for the years 2007–2009. Investigation of the O–C diagram shows that further monitoring of the epochs of eclipse minima of CT Her will cast new light on the evolution of its orbital period.

Sct star HD 129231

Context. Short-period high-amplitude pulsating stars of Population I (δ Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. Aims. We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O–C) short-term analyses. Methods. An investigation of the O–C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. Results. In addition to a positive (161 ± 3) × 10 −9 yr −1 secular relative increase in the main pulsation period of BL Cam, we detected in the O–C data short- (144.2 d) and long-term (∼3400 d) variations, both incompatible with a scenario of stellar evolution. Conclusions. Interpreted as a light travel-time effect, the short-term O–C variation is indicative of a massive stellar component (0.46 to 1 M� ) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O–C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably ab rown dwarf star (≥0.03 M� ), orbiting in ∼3400 d at a distance of 4.5 AU from the primary.

Multi-site, multi-year monitoring of the oscillating Algol-type eclipsing binary CT Herculis

Proxima Centauri, the star closest to our Sun, is known to host at least one terrestrial planet candidate in a temperate orbit. Here we report the ALMA detection of the star at 1.3 mm wavelength and the discovery of a belt of dust orbiting around it at distances ranging between 1 and 4 au, approximately. Given the low luminosity of the Proxima Centauri star, we estimate a characteristic temperature of about 40 K for this dust, which might constitute the dust component of a small-scale analog to our solar system Kuiper belt. The estimated total mass, including dust and bodies up to 50 km in size, is of the order of 0.01 Earth masses, which is similar to that of the solar Kuiper belt. Our data also show a hint of warmer dust closer to the star. We also find signs of two additional features that might be associated with the Proxima Centauri system, which, however, still require further observations to be confirmed: an outer extremely cold (about 10 K) belt around the star at about 30 au, whose orbital plane is tilted about 45 degrees with respect to the plane of the sky; and additionally, we marginally detect a compact 1.3 mm emission source at a projected distance of about 1.2 arcsec from the star, whose nature is still unknown.

The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign

Context. The study of pulsation in pre-main-sequence intermediate-mass stars represents an important tool for deriving information about fundamental stellar parameters and internal structure, as well as testing theoretical models. Interest in this class of variable stars has increased significantly during the last decade and about 30 members are presently known in the literature. Aims. After constructing the frequency spectrum of oscillations in V346 Ori, we apply asteroseismic tools to these data to estimate the intrinsic parameters (mass, luminosity, effective temperature) of V346 Ori and obtain information about its internal structure. Methods. CCD time-series photometry in the Johnson V filter was obtained for a total of 145.7 h of observations distributed over 36 nights. The resulting light curves were subjected to a detailed frequency analysis using updated numerical techniques. Photometric and spectroscopic data were also acquired to determine reliable estimates of the stellar properties. Results. We identified 13 oscillation frequencies, 6 of which with higher significance. These were compared with the predictions of non-radial adiabatic models. The resulting best-fit model corresponds to a mass of 2.1 ± 0.2 M� , luminosity logL/L� = 1.37 +0.11 −0.13 , and effective temperature 7300 ± 200 K. These values are marginally consistent with the association of V346 Ori to Orion OB1a. Alternatively, V346 Ori could be placed at a slightly larger distance than previously estimated.

ALMA Discovery of Dust Belts around Proxima Centauri

We present the results of simultaneous uvby photometry carried out from 1999 to 2001 of the variable V2109 Cyg together with a spectroscopic analysis based on one high resolution spectrum obtained in 2000. From this study, the star is definitively classified as an evolved Sct-type variable with solar metal abundances. This conclusion is also supported by the detected multiperiodic pulsational behaviour and the observed variation of the m1 index over the pulsation cycle. This variation is slightly reversed relative to the V light curve, in very good agreement with the m1 variation expected from the photometric calibrations. Besides the main frequency f1 = 5:3745 cd 1 and its first harmonic 2 f1, a secondary peak is found at f2= 5:8332 cd 1 ( f1= f2= 0:92) with f1 identified as a radial mode and f2 as non-radial. Whereas no significant variations are found in the amplitude of f1 from season to season, the amplitude of f2 changes strongly. Moreover, the main period has remained constant since 1990, within the observational uncertainties. Additional secondary frequencies may also be excited in this variable.