Francisco Jose Jablonski

Cyclical period changes in the dwarf novae V2051 Oph and V4140 Sgr

We report the identification of cyclical changes in the orbital period of the eclipsing dwarf novae V2051 Ophiuchi and V4140 Sagitarii. We used sets of white dwarf mideclipse timings to construct observed-minus-calculated diagrams covering, respectively, 25 and 16 years of observations. The V2051 Oph data present cyclical variations that can be fitted by a linear plus sinusoidal function with period 22±2 yr and amplitude 17±3 s. The statistical significance of this period by an F-test is larger than 99.9 per cent. The V4140 Sgr data present cyclical variations of similar amplitude and period 6.9 ± 0.3 yr which are statistically significant at the 99.7 per cent level. We derive upper limits for secular period changes of | u P| < 3 × 10 12 and | u P| < 1.8 × 10 11 , respectively for V2051 Oph and V4140 Sgr. We combined our results with those in the literature to construct a diagram of the amplitude versus period of the modulation for a sample of 11 eclipsing cataclysmic variables (CVs). If the cyclical period changes are the consequence of a solar-type magnetic activity cycle in the secondary star, then magnetic activity is a widespread phenomenon in CVs, being equally common among long- and short-period systems. This gives independent evidence that the magnetic field (and activity) of the secondary stars of CVs do not disappear when they become fully convective. We also find that the fractional cycle period changes of the short-period CVs are systematically smaller than those of the long-period CVs.

Spectral atlas of massive stars around

We present a digital atlas of peculiar, high-luminosity massive stars in the near-infrared region (10470-11000 A) at medium resolution (R~7000). The spectra are centered around He I 10830 A, which is formed in the wind of those stars, and is a crucial line to obtain their physical parameters. The instrumental configuration also sampled a rich variety of emission lines of Fe II, Mg II, C I, N I and Pa gamma. Secure identifications for most spectral lines are given, based on synthetic atmosphere models calculated by our group. We also propose that two unidentified absorption features have interstellar and/or circumstellar origin. For the strongest one (10780 A) an empirical calibration between E(B-V) and equivalent width is provided. The atlas displays the spectra of massive stars organized in four categories, namely Be stars, OBA Iape (or luminous blue variables, LBV candidates and ex/dormant LBVs), OB supergiants and Wolf-Rayet stars. For comparison, the photospheric spectra of non emission-line stars are presented. Selected LBVs were observed in different epochs from 2001 to 2004, and their spectral variability reveals that some stars, such as Eta Car, AG Car and HR Car, suffered dramatic spectroscopic changes during this time interval.

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We report strong evidence for a approximately 304 day periodicity in the spin history of the accretion-powered pulsar GX 1+4 that is most probably associated with the orbital period of the system. We have used data from the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory to show a clear periodic modulation of the pulsar frequency from 1991 to date, in excellent agreement with the ephemeris proposed by Cutler, Dennis, & Dolan in 1986. Our results indicate that the orbital period of GX 1+4 is 303.8+/-1.1 days, making it the widest known low-mass X-ray binary system by more than 1 order of magnitude and putting this long-standing question to rest. A likely scenario for this system is an elliptical orbit in which the neutron star decreases its spin-down rate (or even exhibits a momentary spin-up behavior) at periastron passages due to the higher torque exerted by the accretion disk onto the magnetosphere of the neutron star. These results are not inconsistent with either the X-ray pulsed flux light curve measured by BATSE during the same epoch or the X-ray flux history from the All-Sky Monitor on board the Rossi X-Ray Timing Explorer.

10 830 Å

In the course of the Pico dos Dias survey (PDS), we identified the stellar-like object PDS 456 at coordinates a 5 17 h 28 m 19 s d 52 147159550 (epoch 2000), with a relatively nearby (z 5 0.184) and bright (B 5 14.69) quasar. Its position at Galactic coordinates l 5 107 b 51 117 .2, near the bulge of the Galaxy, may explain why it was not detected before. The optical spectrum of PDS 456 is typical of a luminous quasar, showing a broad (FWHM » 4000 km s 21 )H bline, very intense Fe ii lines, and a weak [O iii] l5007 line. PDS 456 is associated to the infrared source IRAS 1725421413 with a 60 mm infrared luminosity L60 5 3.8 # 10 45 ergs s 21 . The relatively flat slopes in the infrared [ a(25, 60) 52 0.33 and a(12, 25) 52 0.78] and a flat power index in the optical (Fn / n 20.72 ) may indicate a low dust content. A good match between the position of PDS 456 and the position of the X-ray source RXS J172819.32141600 implies an X-ray luminosity LX 5 2.8 # 10 44 ergs s 21 . The good correlation between the strength of the emission lines in the optical and the X-ray luminosity, as well as the steep optical to X-ray index estimated (aOX 52 1.64), suggests that PDS 456 is radio quiet. A radio survey previously performed in this region yields an upper limit for radio power at about 5 GHz of approximately 2.6 # 10 30 ergs 21 Hz 21 . We estimate the Galactic reddening in this line of sight to be AB . 2.0, implying an absolute magnitude MB 52 26.7 (using H0 5 75 km s 21 Mpc 21 and q0 5 0). In the optical, PDS 456 is therefore 1.3 times more luminous than 3C 273 and the most luminous quasar in the nearby (z • 0.3) universe. Subject headings: infrared: general — quasars: individual (PDS 456, IRAS 17254 21413) — X-rays: galaxies

The Orbital Period of the Accreting Pulsar GX 1+4

We use the star count model of Ortiz & Lepine to perform an unprecedented exploration of the most important Galactic parameters comparing the predicted counts with the Two Micron All Sky Survey observed star counts in the J, H, and KS bands for a grid of positions covering the whole sky. The comparison is made using a grid of lines of sight given by the HEALPix pixelization scheme. The resulting best-fit values for the parameters are: 2120 ± 200 pc for the radial scale length and 205 ± 40 pc for the scale height of the thin disk, with a central hole of 2070 pc for the same disk, 3050 ± 500 pc for the radial scale length and 640 ± 70 pc for the scale height of the thick disk, 400 ± 100 pc for the central dimension of the spheroid, 0.0082 ± 0.0030 for the spheroid to disk density ratio, and 0.57 ± 0.05 for the oblate spheroid parameter.

Discovery of a Luminous Quasar in the Nearby Universe

We present the first optical circular and linear polarizatio n measurements of two polar candidates from ROSAT: 1RXS J161008.0+035222 and 1RXS J231603.9 052713. We also present H band near-infrared photometry of the last object. The presence of strong circular polarization confirms them as AM Her systems. 1RXS J231603.9 052713 was observed in two different brightness states. The orbital phase dependence of the flux and polarization of 1RXS J161008.0+035222 is reasonably fitted with a simple mod el in which the binary is observed at a small inclination and the magnetic field axis is al most parallel to the white-dwarf rotation axis resulting in the accretion column axis being s een from top during the whole orbital revolution. An alternative geometry with intermediate inclination can fit the observed flux and circular polarization. However, in this case, the mo del produces a linear polarization peak which is not corroborated by the data. The estimated magnetic field is in the 10 to 20 MG range. The circular polarization of 1RXS J231603.9 052713 is complex and highly variable. The light-curves of that object have been fitted using a model which includes the white-dwarf, a heated secondary and a point-like accretion region. The secondary emission contributes significantly even in optical wavelengths. This model also repr oduces the main features of the optical polarization of 1RXS J231603.9 052713. We estimate the main parameters of the binary, of the accretion region and the distance to the syste m. An improved description of this system should include an extended and inhomogeneous accreting region as well as non-radial accretion.

A galaxy model from two micron all sky survey star counts in the whole sky, including the plane

The discovery of a coherent photometric modulation in Nova Oph 1988 with period 0.117515 +/- 0.000002 d, which is associated with the orbital period of the underlying binary, is reported. On the basis of photometric observations, it is concluded that Nova V2214 Oph 1988 is a magnetic nova with an orbital period inside the period gap. The inclusion of this system in the statistics of novae suggests that there is no period gap for novae and that there is a clear correlation between the occurrence of novae with short orbital periods and the presence of magnetic white dwarfs. It is suggested that funneling of the accretion flow onto the magnetic poles favors the conditions for a thermonuclear runaway, increasing the frequency of eruptions for magnetic systems.

Optical polarimetry and infrared photometry of two AM Her binaries: 1RXS J161008.0+035222 and 1RXS J231603.9−052713

We describe the “Monitor e Imageador de Raios-X” (MIRAX), an X-ray astronomy satellite mission proposed by the high-energy astrophysics group at the National Institute for Space Research (INPE) in Brazil to the Brazilian Space Agency. MIRAX is an international collaboration that includes, besides INPE, the University of California San Diego, the University of Tubingen in Germany, the Massachusetts Institute of Technology and the Space Research Organization Netherlands. The payload of MIRAX will consist of two identical hard X-ray cameras (10–200 keV) and one soft X-ray camera (2–28 keV), both with angular resolution of ∼5–7′. The basic objective of MIRAX is to carry out continuous broadband imaging spectroscopy observations of a large source sample (∼9 months/yr) in the central Galactic plane region. This will allow the detection, localization, possible identification, and spectral/temporal study of the entire history of transient phenomena to be carried out in one single mission. MIRAX will have sensitivities of ∼ 5 mCrab/day in the 2–10 keV band (∼2 times better than the All Sky Monitor on Rossi X-ray Timing Explorer) and 2.6 mCrab/day in the 10–100 keV band (∼40 times better than the Earth Occultation technique of the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory). The MIRAX spacecraft will weigh about 200 kg and is expected to be launched in a low-altitude (∼600 km) circular equatorial orbit around 2007/2008.

Nova V2214 Ophiuchi 1988 : a magnetic nova inside the period gap

We present BVRI CCD aperture polarization and near-infrared photometry of the proto-planetary nebula Hen 3-1475. Its intrinsic polarization is high and shows a strong spectral dependence. The position angles in all bands are perpendicular to the axis of the observed bipolar structure. A Monte Carlo code is used to model the intrinsic polarization of Hen 3-1475. Using disk dimensions and other constraints suggested by previous works, we are able to reproduce the observations with an optically thick disk composed by grains with a power-law size distribution ranging from 0.06 to 0.22 μm. We also reliably estimate the foreground polarization from hundreds of stars contained in the CCD images. It is parallel to the intrinsic polarization of Hen 3-1475. Possible implications of this result are discussed. From IR observations, we estimate an interstellar reddening, AV, of about 3.2.

MIRAX: a Brazilian X-ray astronomy satellite mission

Context. Activity in low-mass stars is an important ingredient in their evolution. Fundamental physical properties such as age, rotation, and magnetic field are correlated with activity. Aims. We show that two components of the low-mass triple system LHS 1070 exhibit strong flaring activity. We identify the flaring components and obtained an improved astrometric solution for the LHS 1070 A/(B +C )s ystem. Methods. Time-series CCD observations were used to monitor LHS 1070 in the B and IC bands. H-band data were used to obtain accurate astrometry for the LHS 1070 A/(B+C )s ystem. Results. We find that two components of the triple system LHS 1070 exhibit photometric activity. We identified components A and B as the flaring objects. We estimate the total energy, ∼2.0 × 10 33 erg, and the magnetic field strength, ∼5.5 kG, of the flare observed in LHS 1070 B. This event has one of the largest amplitudes, ΔB 8.2 mag, ever observed in a flare star.