The multiwavelength variability of 3C 273 Soldi, S.; Türler, M.; Paltani, S. ...
Astronomy and astrophysics (Berlin),
08/2008, Letnik:
486, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Aims. We present an update of the 3C 273's database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the ...multiwavelength properties of this quasar, especially focussing on its variability behaviour. Methods. We study the amplitude of the variations and the maximum variability time scales across the broad-band spectrum and correlate the light curves in different bands, specifically with the X-rays, to search for possible connections between the emission at different energies. Results. 3C 273 shows variability at all frequencies, with amplitudes and time scales strongly depending on the energy and being the signatures of the different emission mechanisms. The variability properties of the X-ray band imply the presence of either two separate components (possibly a Seyfert-like and a blazar-like) or at least two parameters with distinct timing properties to account for the X-ray emission below and above ~20 keV. The dominant hard X-ray emission is most probably not due to electrons accelerated by the shock waves in the jet as their variability does not correlate with the flaring millimeter emission, but seems to be associated to long-timescale variations in the optical. This optical component is consistent with being optically thin synchrotron radiation from the base of the jet and the hard X-rays would be produced through inverse Compton processes (SSC and/or EC) by the same electron population. We show evidence that this synchrotron component extends from the optical to the near-infrared domain, where it is blended by emission of heated dust that we find to be located within about 1 light-year from the ultraviolet source.
Metal-anodic aluminum oxide (AAO)–Al nanostructures have been deposited by using sputtering for the metal layer deposition and a two-step anodization process in different electrolytes to produce ...self-ordered anodic aluminum oxide films. The effect of the morphological parameters of AAO films (such as thickness, pore diameter, interpore distance, and porosity) on the optical properties was studied. The UV–vis reflectance properties as a function of the thickness for the different electrolytes of metal-AAO–Al films were analyzed in order to obtain the color diagrams and the effective refractive indexes of the films. The effective refractive index was found to depend on the thickness and porosity of AAO films. The change in color observed in metal-AAO–Al nanostructures is due to the thickness and porosity of the AAO films. In order to verify the experimental results, UV–vis reflectance spectra of AAO–Al films were simulated using commercially available finite element simulation software.
Context. The EROS-2 survey has produced a database of millions of time series from stars monitored for more than six years, allowing us to classify some of their sources into different variable star ...types. Among the so-called, long period variables (LPVs), which are known to follow particular sequences in the period-luminosity diagram, we find long secondary period variables whose variability origin remains a matter of debate. Aims. We analyze data for the 856 864 variable stars that have been discovered in the Large Magellanic Cloud (LMC) that are present in the EROS-2 database, to detect, classify, and characterize LPVs. Methods. Our method for identifying LPVs is based on the statistical Abbe test. It investigates the regularity of the light curve with respect to the survey duration in order to extract candidates with long-term variability. The period search is performed using Deeming, Lomb-Scargle, and generalized Lomb-Scargle methods, combined with a Fourier series fit. Color − magnitude, period-magnitude, and period-amplitude diagrams are used to characterize our candidates. Results. We present a catalog of 43 551 LPV candidates for the Large Magellanic Cloud. For each of them, we provide up to five periods, a mean magnitude in EROS-2, 2MASS, and Spitzer bands, BE − RE color, RE amplitude, and spectral type. We use infrared data to distinguish between RGB, O-rich, C-rich, and extreme AGB stars. Properties of our LPV candidates are investigated by analyzing period-luminosity and period-amplitude diagrams.
Context.Light curves of the long-period Algols are known for their complex shape (asymmetry in the eclipse, light variations outside the eclipse, changes from cycle-to-cycle), but their ...interpretation is not possible in the standard model of binary stars. Aims. We determined that complex structures present in these active Algol systems could be studied with the eclipse-mapping method that was successfully applied to the new 7-color photometric observations in the Geneva system of W Cru, belonging to the isolated group of these active Algols. Methods. Several cycles of this long-period (198.5 days) eclipsing binary were covered by observations. We used a modified Rutten's approach to the eclipse-mapping. The optimization of the system's parameters and the recovery of the disk intensity distribution are performed using a genetic algorithm (GA). Results.The finding of a primary (hot) component is hidden in thick accretion disk confirms previous solutions. The mass of the primary component, $M_{1} = 8.2$ $M_{\odot}$, indicates that it is a mid-B type star. The mass-losing component fills its critical lobe, which, for the system's parameters, means it is a G-type supergiant with a mass $M_{2} = 1.6$ $M_{\odot}$. The disk is very extended geometrically, and its outer radius is about 80% of the primary's critical lobe. A reconstructed image reveals the rather clumpy and nonuniform brightness distribution of an accretion disk rim in this system that is seen almost edge-on. This clumpiness accounts for light curve distortions and asymmetries, as well as for secular changes.
Outbursts in the Be star HR 2501 Carrier, F.; Burki, G.
Astronomy and astrophysics (Berlin),
04/2003, Letnik:
401, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Be star HR 2501 was monitored in photometry, from 1978 to 1998 in the Geneva system and from 1990 to 1992 by the Hipparcos satellite, and in spectroscopy from 1998 to 2001 by using the Coralie ...spectrograph. Several mostly unrelated periods or time scales characterize the variability of HR 2501. First, the radial velocity data reveals that this is a new λ Eri star, with a period of 0.79187 d due to non-radial pulsations or clouds close to the stellar photosphere. Second, both Geneva and Hipparcos photometries exhibit a mid- to long-term variability of characteristic time ~500 d and peak-to-peak amplitude ~0.4 mag, most probably a consequence of the recurrent outbursts of matter from the rapidly rotating Be star towards its disk. Third, a characteristic time of ~300 d between the outbursts is shown by spectroscopy by looking at the variations of the equivalent width of Hα, Hβ and HeI (5875.6 Å) emission lines (the outbursts studied in photometry and spectroscopy are unfortunately not the same due to the non-simultaneity of the monitorings). Fourth, the $V/R$ ratio of the double peaks in Hα and Hβ show a periodic-type variation during the second of the spectroscopic outbursts, with periods of respectively 16.7 and 15.1 d, in agreement with the prediction of the dynamical evolution of a blob of material ejected from the equator of the star into the Keplerian disk. Fifth, a short-term photometric period of 0.46 d is detected during an epoch of intensive monitoring; however, it must be noted that if this variability is confirmed, the value of this short-term period is unsure. The other main results are: i) During the 27 months of the spectroscopic survey, in addition to the mentioned outbursts, the emission in Hα and Hβ lines decreased progressively until it almost completely vanishes at the end. ii) The estimated radius of the circumstellar disk varies and reaches 5.5, 4 and 2 stellar radii at maximum for the Hα, Hβ and HeI emission regions respectively; iii) The spectroscopic monitoring was particularly successful, and the series of observation of the line profiles, with the variation of the emission from day to day, is quite exceptional in the studies of Be stars.
The semi-detached eclipsing binary system
V621 Cen (
P
=
3.68
d) has been analysed using the Wilson–Devinney program, on the basis of light curves obtained in the
Geneva 7-colour photometric system, ...and radial velocity curves for both components measured with the cross-correlation technique. The physical and orbital parameters have been determined through a self-consistent simultaneous solution of the photometric and radial velocity curves. The effective temperature of the primary component has been determined from the photometric analysis,
T
eff
1
=
15
,
600
±
800
K
.
The absolute elements of the components are for the primary (mass gainer), with the value of
T
eff
1
fixed,
M
1
=
6.10
±
0.10
M
⊙,
R
1
=
4.58
±
0.01
R
⊙,
M
bol
1
=
-
2.83
±
0.01
, and for the secondary (mass loser),
M
2
=
2.09
±
0.04
M
⊙,
R
2
=
5.87
±
0.01
R
⊙,
M
bol
2
=
-
0.86
±
0.01
,
T
eff
2
=
8750
±
20
K
. The semi-major axis
A of the relative orbit is 20.20
±
0.12
R
⊙. The estimated spectral types of the components are about B3/4
V (primary) and A0/1III (secondary). The equatorial rotational velocity of the primary is 63
km
s
−1. The distance to
V621 Cen is evaluated to 1550
±
140
pc, and the colour excess
E
B2
−
V1 to 0.270
±
0.045.
High aspect ratio ZnO nanowires have been uniformly grown into anodic aluminum oxide (AAO) templates by electrodeposition at a constant potential using peroxide solution. The influence of the ZnCl 2 ...to H 2 O 2 concentration ratio, reduction potential and electrodeposition temperature on the diffusion mechanism, filling ratio, morphology and crystallographic orientation of ZnO nanowires is studied. A correlation between the electrodeposition parameters, through the diffusion mechanism, and the morphological and structural properties of the ZnO nanowire arrays is presented. The diffusion coefficient was found to depend on the zinc chloride concentration, reduction potential and electrodeposition temperature for the electrodeposition of ZnO nanowires into AAO templates. The filling ratio was found to be influenced by the reduction potential and electrodeposition temperature. The morphology of ZnO nanowires is affected by the ZnCl 2 concentration and reduction potential, but not by the deposition temperature. The crystallographic orientation of the ZnO nanowires depends on the reduction potential. These nanowires exhibit a high aspect ratio and uniform growth up to 50 μm thickness into AAO templates.
Four Be stars, HR 1960, HR 2968, HR 3237 and HR 3642, selected according to their periodic variations in Hipparcos and Geneva photometries, were monitored from 1998 until 2001 with the Coralie ...spectrograph. Among these stars, two are new spectroscopic binaries and one is a new λ Eri short period variable. HR 1960 is a low amplitude (K = 3.4 km s-1) SB1 with a period of 395.48 d in agreement with the photometric prediction. HR 3237 is a short period SB1 (P = 5.1526 d). HR 3642 presents some interesting variations in photometry and spectroscopy: indeed, a mid- and a short-term variation is present with periods of 137.99 d (Hp magnitude) and 1.13028 d (radial velocity) respectively. The short-term variation, characteristic of the λ Eri stars, probably implies non-radial pulsations or inhomogeneities in the corotating disc. The last star, HR 2968, is an excellent photometric binary candidate, but no spectroscopic obviousness of a companion has been found.
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