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J. H. Pena

Publications and source records attributed to J. H. Pena.

16 recordsLinked to original sources
arXiv2018

The Delta Scuti star 38 Eri from the ground and from space

We present and discuss the pulsational characteristics of the Delta Scuti star 38 Eri from photometric data obtained at two widely spaced epochs, partly from the ground (1998) and partly from space (MOST, 2011). We found 18 frequencies resolving the discrepancy among the previously published frequencies. Some of the frequencies appeared with different relative amplitudes at two epochs, however, we carried out investigation for amplitude variability for only the MOST data. Amplitude variability was found for one of three frequencies that satisfy the necessary frequency criteria for linear-combination or resonant-mode coupling. Checking the criteria of beating and resonant-mode coupling we excluded them as possible reason for amplitude variability. The two recently developed methods of rotational-splitting and sequence-search were applied to find regular spacings based only on frequencies. Doublets or incomplete multiplets with l=1, 2 and 3 were found in the rotational splitting search. In the sequence search method we identified four sequences. The averaged spacing, probably a combination of the large separation and the rotational frequency, is 1.724+/-0.092 d-1. Using the spacing and the scaling relation $\barρ= [0.0394, 0.0554]$ gcm$^{-3}$ was derived. The shift of the sequences proved to be the integer multiple of the rotational splitting spacing. Using the precise MOST frequencies and multi-colour photometry in a hybrid way, we identified four modes with l=1, two modes with l=2, two modes with l=3, and two modes as l=0 radial modes.

astro-ph.SR↗
arXiv2014

Searching for short-period variable stars in the direction of Coma Berenices and Upgren 1 open clusters: Melotte 111 AV 1224 a new eclipsing binary star

We report the results of CCD photometric observations in the direction of the Coma Berenices and Upgren 1 open clusters with the aim at searching for new short-period variable stars. A total of 35 stars were checked for variability. As a result of this search the star designated in the SIMBAD database as Melotte 111 AV 1224 was found to be a new eclipsing binary star. Follow-up Strömgren photometric and spectroscopic observations allowed us to derive the spectral type, distance, reddening and effective temperature of the star. A preliminary analysis of the binary light curve was performed and the parameters of the orbital system were derived. From the derived physical parameters we conclude that Melotte 111 AV 1224 is most likely a W UMa eclipsing binary that is not a member of the Coma Berenices open cluster. On other hand, we did not find evidence of brightness variations in the stars NSV 5612 and NSV 5615 previously catalogued as variable stars in Coma Berenices open cluster.

astro-ph.SR↗
arXiv2013

Characterizing the variability of Melotte 111 AV 1224: a new variable star in the Coma Berenices open cluster

A search for new pulsating stars in the Coma Berenices open cluster was carried out. As a result of this search the cluster member Melotte 111 AV 1224 presented clear indications of photometric variability. In order to determine its physical parameters Strömgren standard indices and low-resolution spectra were acquired. In this work we present the preliminary results of these observations.

astro-ph.SR↗
arXiv2012

Physical parameters of three field RR Lyrae stars

Strömgren $uvby-β$ photometry of the stars classified as RR Lyrae stars RU Piscium, SS Piscium and TU Ursae Majoris has been used to estimate their iron abundance, temperature, gravity and absolute magnitude. The stability of the pulsating period is discussed. The nature of SS Psc as a RRc or a HADS is addressed. The reddening of each star is estimated from the Strömgren colour indices and reddening sky maps. The results of three approaches to the determination of [Fe/H], $T_{\rm eff}$ and $\log(g)$ are discussed: Fourier light curve decomposition, the Preston $ΔS$ index and the theoretical grids on the $(b-y)_o - c_1{_o}$ plane.

astro-ph.GA↗
arXiv2011

$uvby-β$ photoelectric photometry of the open clusters NGC 6811 and NGC 6830

From $uvby-β$ photometry of the open clusters NGC 6811 (75 stars), and NGC 6830 (19 stars) we were able to determine membership of the stars to each cluster, and fix the age and reddening for each. Since several short period stars have recently been found, we have carried out a study of these variables.

astro-ph.SR↗
arXiv2010

Preliminary results from the STEPHI2009 campaign on the open cluster NGC 1817

We present preliminary observational results of the multi-site STEPHI campaign on the cluster NGC 1817. The three observatories involved are San Pedro Martir (Mexico), Xing Long (China) and the Observatorio del Teide (Spain) - giving an ideal combination to maximise the duty cycle. The cluster has 12 known delta Scuti stars and at least two detached eclipsing binary systems. This combination of characteristics is ideal for extracting information about global parameters of the targets, which will in turn impose strict constraints on the stellar models. From an initial comparison with stellar models using the known fundamental parameters, and just the observed pulsation frequencies and measured effective temperatures, it appears that a lower value of initial helium mass fraction will most likely explain the observations of these stars.

astro-ph.SR↗
arXiv2009

Strömgren photometry and spectroscopy of the Delta Scuti stars 7 Aql and 8 Aql

Photometric $(ubvy-β$) and spectroscopic observations of the $δ$ Scuti variables \astrobj{7 Aql} and \astrobj{8 Aql} are described. The Strömgren standard indices and physical parameters of both stars are derived. Spectral types of F0V and F2III have been assigned to \astrobj{7 Aql} and \astrobj{8 Aql} respectively considering the results from both spectroscopy and photometry. Differential $uvby$ light curves were also analyzed. A attempt of multicolour mode identification is carried out.

astro-ph.SR↗
arXiv2009

Stromgren Photometry of the Delta Scuti Stars 7 Aql and 8 Aql

The preliminary results of new photometric observations of the $δ$ Scuti stars 7 Aql and 8 Aql are reported. 51 hr of $uvby-β$ photoelectric photometric data were obtained over the period June and July 2007 at the San Pedro Mártir Observatory, Mexico. Period analyses confirm the three pulsation modes discovered in 8 Aql in the framework of the STEPHI 2003 multisite campaign. For the star 7 Aql we were able to detect only the main pulsation modes. The standard magnitudes of both stars are obtained. The frequency, amplitude and phases of the frequency modes in different filters are presented.

astro-ph.SR↗
arXiv2008

On the variability of HD 170699 - a possible COROT target

We present the analysis of the variability of HD 170699, a COROT star showing the characteristics of a non evolutionary Delta Scuti star with high rotational velocity. There is a clear period of 10.45 c/d with 5.29 mmag amplitude in the y filter. From the data, it can be seen that the star shows multi-periodicity and it is necessary to add more frequencies to adjust the observations

astro-ph↗
arXiv2008

On the nature of Delta Scuti star HD 115520

Observing Delta Scuti stars is most important as their multi-frequency spectrum of radial pulsations provide strong constraints on the physics of the stars interior; so any new detection and observation of these stars is a valuable contribution to asteroseismology. While performing uvby-beta photoelectric photometry of some RR Lyrae stars acquired in 2005 at the Observatorio Astronomico Nacional, Mexico, we also observed several standard stars, HD115520 among them. After the reduction this star showed indications of variability. In view of this, a new observing run was carried out in 2006 during which we were able to demonstrate its variability and its nature as a Delta Scuti star. New observations in 2007 permitted us to determine its periodic content with more accuracy. This, along with the uvby-beta photoelectric photometry allowed us to deduce its physical characteristics and pulsational modes.

astro-ph↗
arXiv2008

CCD Photometry of Delta Scuti stars 7 Aql and 8 Aql

As a continuation of the study of the Delta Scuti stars 7 Aql and 8 Aql; new CCD photometric data were acquired in 2007. We present a period analysis on these data that confirm the dominant modes detected in each star in the framework of the STEPHI XII campaign in 2003.

astro-ph↗
arXiv2007

uvby--beta photoelectric photometry of NGC 7063

From uvby photometry of 75 stars in the direction of NGC 7063 we were able to determine membership of some stars and fix the distance (722 +- 105 pc), log age (of 8.146) and reddening (E(b-y) = 0.091 +- 0.039 mag) for the cluster.

astro-ph↗
arXiv2007

On the nature of Delta Scuti star HD 115520

As a continuation of the study of the newly found Delta Scuti star HD 115520, we present a period analysis of recently acquired photometric data covering four nights, as well as some conclusions on the nature of this star.

astro-ph↗
arXiv2007

Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003

We present an analysis of the pulsation behaviour of the Delta Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the framework of STEPHI XII campaign during 2003 June--July. 183 hours of high precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained following a classical scheme of multi-channel photometry. Observations in different filters were also obtained and analyzed. Six and three frequencies have been unambiguously detected above a 99% confidence level in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql respectively. A comparison of observed and theoretical frequencies shows that 7 Aql and 8 Aql may oscillate with p modes of low radial orders, typical among Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial oscillations have to be present in both stars as well. The expected range of excited modes according to a non adiabatic analysis goes from n=1 to n=6 in both stars.

astro-ph↗