[Show abstract][Hide abstract] ABSTRACT: In 2008–2013, we obtained 11333 CCD BVI c frames for 57 Cepheids from the General Catalogue of Variable Stars. We performed our observations with the 76-cm telescope of the South African Astronomical Observatory (SAAO, South Africa) and the 40-cm telescope of the Cerro Armazones Astronomical Observatory of the Universidad Católica del Norte (OCA, Chile) using the SBIG ST-10XME CCD camera. The tables of observations, the plots of light curves, and the current light elements are presented. Comparison of our light curves with those constructed from photoelectric observations shows that the differences between their mean magnitudes exceed 005 in 20% of the cases. This suggests the necessity of performing CCD observations for all Cepheids.
[Show abstract][Hide abstract] ABSTRACT: We use UCAC4 proper motions and WISE W1-band apparent magnitudes
intensity-mean for almost 400 field RR Lyrae variables to determine the
parameters of the velocity distribution of Galactic RR Lyrae population and
constrain the zero points of the metallicity- relation and those of the
period-metallicity- -band and period-metallicity- -band luminosity
relations via statistical parallax. We find the mean velocities of the halo-
and thick-disc RR Lyrae populations in the solar neighbourhood to be (U0(Halo),
V0(Halo), W0(Halo)) = (-7 +/- 9, -214 +/- 10, -10 +/- 6) km/s and (U0(Disc),
V0(Disc), W0(Disc)) =(-13 +/- 7, -37 +/- 6, -17 +/- 4) km/s, respectively, and
the corresponding components of the velocity-dispersion ellipsoids, (sigma
VR(Halo), sigma Vphi(Halo), sigma Vtheta(Halo)) = (153 +/- 9, 101 +/- 6, 96 +/-
5) km/s and (sigma VR(Disc), sigma Vphi(Disc), sigma Vtheta(Disc)) = (46 +/- 7,
37 +/- 5, 27 +/- 4) km/s, respectively. The fraction of thick-disc stars is
estimated at 0.22 +/- 0.03. The corrected IR period-metallicity-luminosity
relations are = -0.769 +0.088 [Fe/H]- 2.33 mathoprm log PF and =
-0.825 + 0.088 [Fe/H] -2.33 mathoprm log PF, and the optical
metallicity-luminosity relation, [Fe/H]- , is = +1.094 + 0.232 [Fe/H],
with a standard error of +/- 0.089, implying an LMC distance modulus of 18.32
+/- 0.09, a solar Galactocentric distance of 7.73 +/- 0.36 kpc, and the M31 and
M33 distance moduli of DM(M31) = 24.24 +/- 0.09 (D = 705 +/- 30 kpc) and
DM(M33) = 24.36 +/- 0.09 (D = 745 +/- 31 kpc), respectively. Extragalactic
distances calibrated with our RR Lyrae star luminosity scale imply a Hubble
constant of ~80 km/s/Mpc. Our results suggest marginal prograde rotation for
the population of halo RR Lyraes in the Milky Way.
Monthly Notices of the Royal Astronomical Society 08/2013; 435(4). · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Variations in the pulsation arrival time of five independent pulsation
frequencies of the DB white dwarf EC 20058-5234 individually imitate the
effects of reflex motion induced by a planet or companion but are inconsistent
when considered in unison. The pulsation frequencies vary periodically in a
12.9 year cycle and undergo secular changes that are inconsistent with simple
neutrino plus photon-cooling models. The magnitude of the periodic and secular
variations increases with the period of the pulsations, possibly hinting that
the corresponding physical mechanism is located near the surface of the star.
The phase of the periodic variations appears coupled to the sign of the secular
variations. The standards for pulsation-timing-based detection of planetary
companions around pulsating white dwarfs, and possibly other variables such as
subdwarf B stars, should be re-evaluated. The physical mechanism responsible
for this surprising result may involve a redistribution of angular momentum or
a magnetic cycle. Additionally, variations in a supposed combination frequency
are shown to match the sum of the variations of the parent frequencies to
remarkable precision, an expected but unprecedented confirmation of theoretical
The Astrophysical Journal 02/2013; 765(1). · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on analysis of 308.3 hrs of high speed photometry targeting the
pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole
Earth Telescope (WET) during the 2008 international observing run XCOV26. The
Fourier transform of the light curve contains 19 independent frequencies and
numerous combination frequencies. The dominant peaks are 1633.907, 1887.404,
and 2504.897 microHz. Our analysis of the combination amplitudes reveals that
the parent frequencies are consistent with modes of spherical degree l=1. The
combination amplitudes also provide m identifications for the largest amplitude
parent frequencies. Our seismology analysis, which includes 2004--2007 archival
data, confirms these identifications, provides constraints on additional
frequencies, and finds an average period spacing of 41 s. Building on this
foundation, we present nonlinear fits to high signal-to-noise light curves from
the SOAR 4.1m, McDonald 2.1m, and KPNO 2m telescopes. The fits indicate a
time-averaged convective response timescale of 99.4 +/- 17 s, a temperature
exponent 85 +/- 6.2 and an inclination angle of 32.9 +/- 3.2 degrees. We
present our current empirical map of the convective response timescale across
the DA instability strip.
The Astrophysical Journal 04/2012; 751(2). · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Photometric data in the UBV(RI)c system have been acquired for 80 solar
analog stars for which we have previously derived highly precise atmospheric
parameters Teff, log g, and [Fe/H] using high resolution, high signal-to-noise
ratio spectra. UBV and (RI)c data for 46 and 76 of these stars, respectively,
are published for the first time. Combining our data with those from the
literature, colors in the UBV(RI)c system, with ~0.01 mag precision, are now
available for 112 solar analogs. Multiple linear regression is used to derive
the solar colors from these photometric data and the spectroscopically derived
Teff, log g, and [Fe/H] values. To minimize the impact of systematic errors in
the model-dependent atmospheric parameters, we use only the data for the ten
stars that most closely resemble our Sun, i.e., the solar twins, and derive the
following solar colors: (B-V)=0.653+/-0.005, (U-B)=0.166+/-0.022,
(V-R)=0.352+/-0.007, and (V-I)=0.702+/-0.010. These colors are consistent,
within the 1 sigma errors, with those derived using the entire sample of 112
solar analogs. We also derive the solar colors using the relation between
spectral line-depth ratios and observed stellar colors, i.e., with a completely
model-independent approach, and without restricting the analysis to solar
twins. We find: (B-V)=0.653+/-0.003, (U-B)=0.158+/-0.009, (V-R)=0.356+/-0.003,
and (V-I)=0.701+/-0.003, in excellent agreement with the model-dependent
The Astrophysical Journal 04/2012; 752(1). · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A total of total of 1071 B, V, Ic-band CCD frames are taken for three
GCVS RR Lyr-type variables (CL Eri, CM Eri, and CN Eri), for which only
coordinates were known. Observations were made with the 76-cm telescope
of the South African Astronomical Observatory using an SBIG CCD
ST-10XME. The inferred periods and light-curves confirm that CL Eri
(P=0.644d), which was found to exhibit the Blazhko effect, and CN Eri
(P=0.580d) are RR Lyr-type variables. CM Eri is most probably a
Population-Il Cepheid with a period of 0.824d.
(1 data file).
[Show abstract][Hide abstract] ABSTRACT: We took a total of 1175 B, V, and Ic-band CCD frames for 11 GCVS RR
Lyr-type variables, for which only the coordinates were known.
Observations were made with the 76-crn telescope of the South African
Astronomical Observatory. We confirm the variability types, determine
the periods, and build the light curves for five objects: BL Aps
(P=0.598d), GR Pav (P=0.583d), HI Pav (P=0.643d), HZ Pav (P=0.803d), and
IR Pav (P=0.561d). The objects SY Aps (P=0.279d) and IV Pav (P=0.408d)
proved to be W UMa-type eclipsing variables; TW Aps (P=0.149d), an SX
Phe-type variable; TT Aps (P=482d), an SRD-type semiregular variable,
and SW Aps and GI Pav, constant stars.
(2 data files).
[Show abstract][Hide abstract] ABSTRACT: In 2008-2010, we obtained 6095 CCD frames in the BVIc photometric system for 49 classical Cepheids discovered in the ASAS-3 project. The observations were obtained on the 76-cm telescope of the South African Astronomical Observatory (SAAO, RSA) and the 40-cm telescope of the Cerro Armazones Observatory of the Catholic University of the North (OCA, Chile), with a SBIGCCD ST-10XME camera. We present tabulated observations, light curves, and revised elements for the brightness variations. (2 data files).
[Show abstract][Hide abstract] ABSTRACT: In 2008-2010, we obtained 6095 CCD frames in the BV I c photometric systemfor 49 classical Cepheids discovered in the ASAS-3 project. The observations were obtained on the 76-cm telescope of the South African Astronomical Observatory (SAAO, RSA) and the 40-cm telescope of the Cerro Armazones Observatory of the Catholic University of the North (OCA, Chile), with a SBIGCCD ST-10XME camera. We present tabulated observations, light curves, and revised elements for the brightness variations.
[Show abstract][Hide abstract] ABSTRACT: We present new results from an ongoing programme to study the dust extragalactic extinction law in E/S0 galaxies with dust lanes with the Southern African Large Telescope (SALT) during its performance verification phase. The wavelength dependence of the dust extinction for seven galaxies is derived in six spectral bands ranging from the near-ultraviolet atmospheric cut-off to the near-infrared. The derivation of an extinction law is performed by fitting model galaxies to the unextinguished parts of the image in each spectral band, and subtracting from these the actual images. We compare our results with the derived extinction law in the Galaxy and find them to run parallel to the Galactic extinction curve with a mean total-to-selective extinction value of RV= 2.71 ± 0.43. We use total optical extinction values to estimate the dust mass for each galaxy, compare these with dust masses derived from IRAS measurements, and find them to range from 104 to 107 M⊙. We study the case of the well-known dust-lane galaxy NGC 2685 for which Hubble Space Telescope/Wide Field Planetary Camera 2 (HST/WFPC2) data are available to test the dust distribution on different scales. Our results imply a scale-free dust distribution across the dust lanes, at least within ∼1 arcsec (∼60 pc) regions.
Monthly Notices of the Royal Astronomical Society 11/2010; 409(2):727 - 736. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Non-radial pulsations in the primary white dwarfs of cataclysmic variables can now potentially allow us to explore the stellar interior of these accretors using stellar seismology. In this context, we conducted a multi-site campaign on the accreting pulsator SDSS J161033.64–010223.3 (V386 Ser) using seven observatories located around the world in 2007 May over a duration of 11 days. We report the best-fit periodicities here, which were also previously observed in 2004, suggesting their underlying stability. Although we did not uncover a sufficient number of independent pulsation modes for a unique seismological fit, our campaign revealed that the dominant pulsation mode at 609 s is an evenly spaced triplet. The even nature of the triplet is suggestive of rotational splitting, implying an enigmatic rotation period of about 4.8 days. There are two viable alternatives assuming the triplet is real: either the period of 4.8 days is representative of the rotation period of the entire star with implications for the angular momentum evolution of these systems, or it is perhaps an indication of differential rotation with a fast rotating exterior and slow rotation deeper in the star. Investigating the possibility that a changing period could mimic a triplet suggests that this scenario is improbable, but not impossible. Using time-series spectra acquired in 2009 May, we determine the orbital period of SDSS J161033.64–010223.3 to be 83.8 ± 2.9 minutes. Three of the observed photometric frequencies from our 2007 May campaign appear to be linear combinations of the 609 s pulsation mode with the first harmonic of the orbital period at 41.5 minutes. This is the first discovery of a linear combination between non-radial pulsation and orbital motion for a variable white dwarf.
The Astrophysical Journal 04/2010; 714(2):1702. · 6.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Time-series relative photometry for 14 near-Earth asteroids is presented as well as the aspect data, the observing log, and the derived rotation parameters. For most asteroids several lightcurves are reported, each of which was measured with a different comparison star. For each asteroid a composite lightcurve is included, obtained with the specified synodic rotation period. The period, together with the shifts in magnitude of the individual data sets used in the composite lightcurve, were obtained in a least-square fit of the Fourier series of the specified order. (5 data files).
[Show abstract][Hide abstract] ABSTRACT: Aims: We report first results from our extensive survey of the very small (H > 21.5 mag) near-Earth asteroids. Our aim was to obtain photometric lightcurves for these faint, fast moving objects and to measure their rotation periods and amplitudes of light variations. These parameters can be used to make statistical analysis of the still little known population of the smallest asteroids, test present theories of the YORP effect as well as to study their spin limits, which are connected with their internal structure. Methods: Due to the faintness of the targets and the expected short periods of rotation, observations were performed with the large, 10-m SALT telescope in SAAO (South Africa). For most asteroids, V filter images with exposure times of 5-60 s were obtained with the instrument's SALTICAM's CCD camera. Even though the non-sidereal tracking was not available, the SALTICAM's relatively large field-of-view of 8 arcmin × 8 arcmin helped to perform the relative photometry of the fast-moving targets. Results: The presented asteroids have synodic periods ranging from 77 s to 44 min, effective diameters from 21 to 94 m, and significantly elongated shapes. Photometric tables are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/509/A94
Astronomy and Astrophysics 01/2010; · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report the discovery of the first symbiotic star (V= 21.6, KS= 15.8 mag) in the Local Group dwarf irregular galaxy NGC 6822. This star was identified during a spectral survey of Hα emission-line objects using the Southern African Large Telescope during its performance-verification phase. The observed strong emission lines of H i and He ii suggest a high electron density and T* < 130 000 K for the hot companion. The infrared colours allow us to classify this object as an S-type symbiotic star, comprising a red giant losing mass to a compact companion. The red giant is an asymptotic giant branch (AGB) carbon star, and a semiregular variable, pulsating in the first overtone with a period of 142 d. Its bolometric magnitude is Mbol=−4.4 mag.We review what is known about the luminosities of extragalactic symbiotic stars, showing that most, possibly all, contain AGB stars. We suggest that a much larger fraction of Galactic symbiotic stars may contain AGB stars than was previously realized.
Monthly Notices of the Royal Astronomical Society 05/2009; 395(2):1121 - 1126. · 5.52 Impact Factor