1,720,991 research outputs found
Monitoring the late decline of the old nova RW Ursae Minoris
No full textNew 2003-2006 time-resolved photometric observations of the old nova RW UMi (1956) confirm the QPO nature of the light modulations observed. The analysis of all our historical runs show that QPOs tend to cluster around frequencies 4.96 d-1 and 12.4 d-1 while the historical superhump period remains undetected in our data. Although the two main frequencies observed might appear to be aliases of the superhump frequency 17 d-1, they should be produced by two independent mechanisms. These rather irregular QPOs might be explained by vertical oscillations of the inner regions of the accretion disk and/or by the cyclical generation in the disk of travelling density waves at the co-rotation radius of an inclined magnetic rotator. We find that the post-nova luminosity is decaying at a rate of ~0.03 mag y-1. If RW UMi is an intermediate polar system, during the decline the magnetospheric radius of the accreting white dwarf primary should increase and produce important changes in the periods of QPOs
The sky as a laboratory: an educational project of the Department of Astronomy of the University of Padova
No full text“The Sky as a Laboratory” is an educational project of the Department of Astronomy of the University of Padova aimed to give students a physical approach to astronomy and astrophysics. It is a regional program designed to improve science education in the last two grades of high school, by creating cooperation between scientists and teachers. Currently it is present in 30 high schools around all provinces of the region of Veneto in the North-East of Italy. The close involvement in the didactical activities of high schools teachers is without any doubt the winning strategy of the project. Their enthusiastic participation to teaching and organising
activities attracts each year the attention for sciences of an increasing number of students and suggests new ideas for future educational activities
Exploring Narrow-Line Seyfert 1 Galaxies through the Physical Properties of Their Hosts
Full text linkIn this work we address the still open question of the nature of narrow-line Seyfert 1 galaxies (NLS1s): are they really active nuclei with lower mass black holes (BHs) than Seyfert 1 galaxies (S1s) and quasars? Our approach is based on the recently discovered physical connections between nuclear supermassive BHs and their hosting spheroids (spiral bulges or elliptical galaxies). In particular, we compare BH masses of NLS1s and S1s, analyzing the properties of their hosts by means of spectroscopic and photometric data in the optical wavelength domain. We find that NLS1s fill the low BH mass and bulge luminosity values of the MBH-MB relation, a result strongly suggesting that NLS1s are active nuclei in which less massive BHs are hosted by less massive bulges. The correlation is good, with a relatively small scatter fitting simultaneously NLS1s, S1s, and quasars. On the other hand, NLS1s seem to share the same stellar velocity dispersion range as S1s in the MBH-σ* relation, indicating that NLS1s have a smaller BH/bulge mass ratio than S1s. These two conflicting results support in any case the idea that NLS1s could be young S1s. Finally, we do not confirm the significantly nonlinear BH-bulge relation claimed by some authors.
Partially based on observations made with the Asiago 1.82 m telescope of the Padova Astronomical Observatory
The O I λ8446 emission line in NLS1 galaxies
No full textIn studying Ca II λλλ 8498,8542,8662 spectral region of NLS1, we have observed that 7 NLS1 do not show O I λ 8446 line emission. We have investigated the reasons of this disappearing analysing the excitation mechanism of O I λ 8446 and the physical conditions of BLR that permit its emission. With a preliminary study of BLR properties we have found that O I λ 8446 emission required a density n_H between 1E11 and 1E12 and ionization parameter U between -1.8 and -3 in logarithm
Morphology and photometry of isolated Seyfert galaxies
No full textWe present preliminary results about morphological and photometric analysis of a sample of 35 nearby (z<0.035) and isolated or partially isolated Seyfert galaxies, observed through broad-band BVR filters at the 1.8m Vatican Telescope and the 2.2m ESO-La Silla Telescope. We plotted radial profiles of surface brightness, ellipticity, position angles and deviations of axisymmetry for all galaxies. We also calculated magnitudes and colours and morphological parameters by means of 2D decomposition technique
MASYS. The AKARI spectroscopic survey of Symbiotic Stars in the Magellanic Clouds
Full text linkMASYS is the AKARI spectroscopic survey of Symbiotic Stars in the Magellanic Clouds, and one of the European Open Time Observing Programmes approved for the AKARI (Post-Helium) Phase-3. It is providing the first ever near-IR spectra of extragalactic symbiotic stars. The observations are scheduled to be completed in July 2009
The Starburst -- AGN Connection: a Critical Review
No full textNuclear activity and star formation processes represent two key elements in the evolution of galaxies across the cosmic ages. In spite of very different physical backgrounds, several arguments suggest that they should be closely connected. On the basis of simple theoretical considerations, the transport of appreciable amounts of fuel to the AGN scale is very likely to trigger star formation in the gas. Young stellar populations, in their turn, are expected to affect the properties of the interstellar medium, leading to a complex balance of interactions among nuclear activity and star formation. This scenario is also supported by the observation of super-massive black holes and host galaxy properties, which strongly suggest a common evolutionary track. However, despite several years of extensive investigation, the relationship among the two processes still has to be properly explained. Here we provide a review of some of the most important observations, which are relevant to the issue of the connection among AGN and starburst events. Based on a wide sample of observations, we present an analysis of the spectral signatures connected with AGN and star formation activity. Expanding the concept of the distinction among star forming galaxies and the true active nuclei, we provide systematic evidence for a role of recent starburst events in the circum-nuclear regions of active galaxies and discuss the possibility of its influence onto the AGN environment. We also analyze the age, mass and metallicity properties of star-forming and active galaxies, illustrating that they are arranged in a sequence that is consistent with the identified relation
Hydrogen Balmer emission lines and the complex broad line region structure.
No full textIn this work we investigate the properties of the broad emission line components in the Balmer series of a sample of Type 1 Active Galactic Nuclei (AGN). Using the Boltzmann Plot method as a diagnostic tool for physical conditions in the plasma, we detect a relationship among the kinematical and thermo-dynamical properties of these objects. In order to further clarify the influence of the central engines on the surrounding material, we look for signatures of structure in the broad line emitting regions, that could affect the optical domain of the observed spectra. Using a combination of line profile analysis and kinematical modeling of the emitting plasma, we study how the emission line broadening functions are influenced by different structural configurations. The observed profiles are consistent with flattened structures seen at quite low inclinations, typically with i < 20°. Since this result is in good agreement with some independent observations at radio frequencies, we apply a new formalism to study the properties of AGN central engines
Stellar velocity dispersion in narrow-line Seyfert 1 galaxies
No full textSeveral authors have recently explored, for narrow-line Seyfert 1 galaxies (NLS1s), the relationship between black hole mass (MBH) and stellar velocity dispersion (σ*). Their results are more or less in agreement and seem to indicate that NLS1s fill the region below the fit obtained by Tremaine et al., showing a range of σ* similar to that of Seyfert 1 galaxies, and a lower MBH. Until now, the [OIII] width has been used in place of the stellar velocity dispersion, but some indications have begun to arise against the effectiveness of the gaseous kinematics in representing the bulge potential, at least in NLS1s. Bian & Zhao have stressed the urgency of producing true σ* measurements. Here, we present new stellar velocity dispersions obtained through direct measurements of the CaII absorption triplet (~8550 Å) in the nuclei of eight NLS1 galaxies. The resulting σ* values and a comparison with σ[OIII] confirm our suspicion that [OIII] typically overestimates the stellar velocity dispersion. We demonstrate that NLS1s follow the MBH-σ* relation as Seyfert 1, quasars and non-active galaxies
Nuclear activity and star formation properties of Seyfert 2 galaxies.
No full textIn order to characterize the amount of recent or ongoing stellar formation in the circumnuclear region of active galaxies on a statistically sound basis, we have studied the stellar component of the nuclear spectra in three different samples of galaxies, namely Seyfert 2 galaxies (hereafter S2G), star-forming galaxies (SFG) and passive normal galaxies (NG), i.e., no emission lines observed, using Sloan Digital Sky Survey data (SDSS) (Adelman-McCarthy, 2008). The stellar component of the observed spectra has been extracted using STARLIGHT (Cid Fernandes et al., 2004), which fits an observed spectrum with a model (template) spectrum obtained by combining a library of pre-defined simple stellar populations spectra, with distinct ages and metallicities. The resulting template spectra for the different samples of galaxies have been compared to determine the features of the stellar emission component and to evaluate the presence and intensity of the star formation in the nuclear regions of different families of galaxies. From a first qualitative analysis it results that the shape of the Spectral Energy Distribution (SED) of S2G and NG is very similar, while that of SFG is characterized by a strong blue excess. The presence of the 4000 Å break in the spectra of S2G and NG together with the lack of a strong blue continuum clearly indicate the absence of ongoing star formation in the circumnuclear regions of S2G and obviously of NG. Anyway traces of a recent star formation history are evident in the spectra of S2G galaxies, which show a 4000 Å break systematically shallower than in NG
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