V. Casanova

The AMIGA sample of isolated galaxies - II. Morphological refinement

Received / accepted Abstract. We present a complete refinement of the optical morphologies for galaxies in the Catalog of Isolated Galaxies (Karachentseva 1973) that forms the basis of the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) project. Uniform reclassification using the digitized POSS II benefit ed from the high resolution and dynamic range of that sky survey. Comparison with independent classifications made for an SDS S overlap sample of more than 200 galaxies confirms the reli- ability of the early vs. late-type discrimination and the ac curacy of spiral subtypes withinT = 1-2. CCD images taken at the Observatorio de Sierra Nevada were also used to solve ambiguities in early versus late-type classifications. A consi derable number of galaxies in the catalog (n = 193) are flagged for the presence of nearby companions or sign s of distortion likely due to interaction. This most isolated sample of galaxies in the local Universe is dominated by two populations: 1) 82% spirals (Sa-Sd) with the bulk being luminous systems with small bulges (63% between types Sb-Sc) and 2) a significant population o f early-type E-S0 galaxies (14%). Most of the types later than Sd are low luminosity galaxies concentrated in the local superclus- ter where isolation is diffi cult to evaluate. The late-type spiral majority of the sampl e spans a luminosity range MB−corr =−18 to −22 mag. Few of the E/S0 population are more luminous than−21.0 marking an absence of, an often sought, super L ∗ merger (e.g. fossil elliptical) population. The rarity of high lum inosity systems results in a fainter derived M ∗ for this population com- pared to the spiral optical luminosity function (OLF). The E-S0 population is from 0.2 to 0.6 mag fainter depending how the sample is defined. This marks the AMIGA sample as almost unique among samples that compare early and late-type OLFs sep- arately. In other samples, which always involve galaxies in higher density environments, M ∗/S0 is almost always 0.3-0.5 mag brighter than M ∗, presumably reflecting a stronger correlation between M ∗ and environmental density for early-type galaxies.

A study of short term rotational variability in TNOs and Centaurs from Sierra Nevada Observatory

Broad band CCD observations focused on short-term rotational variability have been carried out for six TNOs: 1999 TD 1 0 , 1999 TC 3 6 , 2000 EB 1 7 3 , (20000) Varuna, (28978) Ixion, 2002 CR 4 6 , and four Centaurs: 2000 QC 2 4 3 , 2001 PT 1 3 , 2002 PN 3 4 and 2002 GO 9 using the 1.5 m telescope at Sierra Nevada Observatory (Granada, Spain) since mid 2001. Three of the bodies exhibit periodic double-peaked lightcurves with amplitudes larger than 0.4 mag while another four show periodic variability with amplitudes below 0.20 mag. Basic physical properties of these objects can be derived or constrained from the observations. Here we present a summary of the main results obtained for these objects.

The γ Doradus CoRoT target HD 49434: I. Results from the ground-based campaign

Context. We present an extensive ground-based photometric and spectroscopic campaign of the γ Dor CoRoT target HD 49434. This campaign was a preparatory step of the CoRoT satellite observations, which occurred between October 2007 and March 2008. Aims. With satellite data, detection of low-degree pulsation modes only is achievable, and, as no filters are available, with poor identification. Ground-based data promise eventually to identify additional modes and provide extra input for the identification: spectroscopic data allows the detection of high-degree modes and an estimate of the azimuthal number m. We attempt to detect and identify as many pulsation modes as possible from the ground-based dataset of the γ Dor star HD 49434, and anticipate the CoRoT results. Methods. We searched for frequencies in the multi-colour variations, the pixel-to-pixel variations across the line profiles, and the moments variations in a large dataset, consisting of both multi-colour photometric and spectroscopic data from different observatories, using different frequency analysis methods. We performed a tentative mode identification of the spectroscopic frequencies using the Moment Method and the Intensity Period Search Method. We also completed an abundance analysis. Results. The frequency analysis clearly indicates the presence of four frequencies in the 0.2−1.7 d −1 interval, as well as six frequencies in the 5−12 d −1 domain. The low frequencies are typical of γ Dor variables, while the high frequencies are common to δ Sct pulsators. We propose that the frequency 2.666 d −1 is the rotational frequency. All modes, for which an identification was possible, appear to be high-degree modes (3 ≤ � ≤ 8). We did not find evidence for a possible binary nature of the star HD 49434. The element abundances that we derived are consistent with values obtained in previous analyses. Conclusions. We classify the γ Dor star HD 49434 as a hybrid pulsator, which pulsates simultaneously in p -a ndg-modes. This implies that HD 49434 is an extremely interesting target for asteroseismic modelling.

Short-term rotational variability of eight KBOs from Sierra Nevada Observatory

In 2001, we started a CCD photometry programme to study the short-term variability of some of the brightest TNOs and Centaurs from the Sierra Nevada observatory. In this paper, we report our latest results on short-term rotational variability of 7 trans-neptunian objects: Orcus (2004 DW), 2002 AW 197 , 2003 AZ 84 , 2003 VS 2 , 2002 VE 95 , 2001 YH 140 , 1996 TL 66 , and a Centaur: 2003 CQ 1 . Analysis of the photometric data revealed confident periodicities for 6 objects, with all the lightcurve amplitudes smaller than 0.2 mag, except for 2003 VS 2 . Considering all the objects for which reliable lightcurve amplitudes have been reported in the literature (32), the new statistics reveal that 31% of the bodies show variability above 0.15 mag, but only 16% of them display larger amplitudes than 0.4 mag. Here we present a summary of the main results obtained for these objects, and discuss the implications for their basic physical properties.

A study of Trans-Neptunian object 55636 (2002 TX300)

We report on physical properties of the bright Trans-Neptunian Object 2003 TX300 based on a large set of observa- tions taken in different wavelength ranges. Broad band CCD observations aimed at studying the short-term rotational variability show a low amplitude periodic signal of 7.89 ± 0.03 h. We cannot yet determine whether the lightcurve is single-peaked (i.e. the rotation period would be 7.89 h) or double-peaked (i.e. the actual spin period would be 15.78 h). From a sinusoidal fit, the peak to peak amplitude of the brightness changes is 0.09 ± 0.08 mag. If the brightness changes are due to irregular shape, this amplitude implies a minimum axial ratio of 1.09. BVRI photometry indicates similar colors as other large Kuiper Belt members, with B − V = 0.64 ± 0.04, V − R = 0.40 ± 0.07, and R − I = 0.22 ± 0.05. Thermal observations at 250 GHz (1.2 mm) result in no confident detection of the body, with a measured flux of 0.22 ± 0.51 mJy. Combining all the data and using the same thermophysical model as in Lellouch et al. (2002) we find (at a 3-σ confidence level) a lower limit for the geometric albedo (pv > 0.06) and an upper limit for the size of this object (D 0.08, which is significantly higher than the typical 0.04 cometary value and also higher than that of Varuna.

Rotational brightness variations in Trans-Neptunian Object 50000 Quaoar

Time-resolved broad-band CCD photometry of Trans-Neptunian Object 50000 Quaoar carried out using the 1.5 m telescope at Sierra Nevada Observatory is presented. The lightcurve reveals short-term variability due to rotation of the body. The periodogram analysis shows a peak at 8.8394 ± 0.0002 h with a confidence level above 99.9%. The lightcurve seems to be double-peaked, and therefore the rotation period would be 17.6788 ± 0.0004 h. The amplitude of the oscillation is 0.133 ± 0.028 mag. Under the assumption that the rotational variation is induced by an irregular shape, the minimum axial ratio of Quaoar would then be 1.133 ± 0.028.

CCD photometric search for peculiar stars in open clusters - VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120

Institute of Astronomy, National Astronomical Observatory, P.O. Box 136, BG-4700 Smolyan, BulgariaReceived 2006 / Accepted 2006ABSTRACTContext. We continue our survey for magnetic chemically peculiar (CP2) stars in galactic open clusters to shed morelight on their origin and evolution.Aims. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at awide range of evolutionary stages. The knowledge of open clusters ages and metallicities can help to find a correlationof these parameters with the (non-)presence of peculiarities which has to be taken into account in stellar evolutionmodels.Methods. The intermediate band ∆a photometric system samples the depth of the 5200˚A flux depression by comparingthe flux at the center with the adjacent regions with bandwidths of 110˚A to 230 ˚A. It is capable to detect magneticCP2 and CP4 stars with high efficiency, but also the groups of (metal-weak) λ Bootis, as well as classical Be/shell starscan be successfully investigated. In addition, it allows to determine the age, reddening and distance modulus with anappropriate accuracy by fitting isochrones.Results. From the 1677 observed members of the eight open clusters, twenty five CP2 and one Ae stars were identified.Further nineteen deviating stars are designated as questionable due to several reasons. The estimated age, reddeningand distance for the programme clusters were compared with published vales of the literature and discussed in thiscontext.Conclusions. The current paper shows that CP2 stars are present continuously in very young (7Myr) to intermediateage (500Myr) open clusters at distances larger than 2kpc from the Sun.Key words. Stars: chemically peculiar – stars: early-type – techniques: photometric – open clusters and associations:general

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.

HD 172189: another step in furnishing one of the best laboratories known for asteroseismic studies

HD 172189 is a spectroscopic eclipsing binary system with a rapidly-rotating pulsating δ Scuti component. It is also a member of the open cluster IC 4756. These combined characteristics make it an excellent laboratory for asteroseismic studies. To date, HD 172189 has been analysed in detail photometrically but not spectroscopically. For this reason we have compiled a set of spectroscopic data to determine the absolute and atmospheric parameters of the components. We determined the radial velocities (RV) of both components using four different techniques. We disentangled the binary spectra using KOREL, and performed the first abundance analysis on both disentangled spectra. By combining the spectroscopic results and the photometric data, we obtained the component masses, 1.8 and 1.7 Mȯ, and radii, 4.0 and 2.4 Rȯ, for inclination i = 73.2°, eccentricity e = 0.28, and orbital period Π = 5.70198 days. Effective temperatures of 7600 K and 8100 K were also determined. The measured v sin i are 78 and 74 km s-1, respectively, giving rotational periods of 2.50 and 1.55 days for the components. The abundance analysis shows [Fe/H] = -0.28 for the primary (pulsating) star, consistent with observations of IC 4756. We also present an assessment of the different analysis techniques used to obtain the RVs and the global parameters.

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

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.