Alfvenic Heating of Protostellar Accretion Disks

We investigate the effects of heating generated by damping of Alfven waves on protostellar accretion disks. Two mechanisms of damping are investigated, nonlinear and turbulent, which were previously studied in stellar winds (Jatenco-Pereira & Opher 1989a, b). For the nominal values studied, f=delta v/v_{A}=0.002 and F=varpi/Omega_{i}=0.1, where delta v, v_{A} and varpi are the amplitude, velocity and average frequency of the Alfven wave, respectively, and Omega_{i} is the ion cyclotron frequency, we find that viscous heating is more important than Alfven heating for small radii. When the radius is greater than 0.5 AU, Alfvenic heating is more important than viscous heating. Thus, even for the relatively small value of f=0.002, Alfvenic heating can be an important source of energy for ionizing protostellar disks, enabling angular momentum transport to occur by the Balbus-Hawley instability.Comment: 21 pages, 9 figures. Accepted for publication in Ap

Emission-Line Properties of the Optical Filaments of NGC 1275

Extended nebular filaments are seen at optical wavelengths in NGC 1275, the central galaxy in the Perseus cluster. The agents responsible for the excitation of these filaments remain poorly understood. In this paper we investigate possible mechanisms for powering the filaments, using measurements from an extensive spectroscopic data set acquired at the Lick Observatory 3-m Shane telescope. The results show that the filaments are in an extremely low ionization and excitation state. The high signal-to-noise ratio of the spectra allows us to measure or place sensitive upper limits on weak but important diagnostic lines. We compare the observed line intensity ratios to the predictions of various ionization models, including photoionization by an active galactic nucleus, shock heating, stellar photoionization, and photoionization by the intracluster medium. We also investigate possible roles for cluster extreme-ultraviolet emission, and filtering of cluster soft X-ray emission by an ionized screen, in the energetics of the filaments. None of these mechanisms provides an entirely satisfactory explanation for the physical state of the nebulae. Heating and ionization by reconnection of the intracluster magnetic field remains a potentially viable alternative, which merits further investigation through Faraday rotation studies.Comment: Accepted for publication in Ap

The Possibility of Thermal Instability in Early-Type Stars Due to Alfven Waves

It was shown by dos Santos et al. the importance of Alfv\'en waves to explain the winds of Wolf-Rayet stars. We investigate here the possible importance of Alfv\'en waves in the creation of inhomogeneities in the winds of early-type stars. The observed infrared emission (at the base of the wind) of early-type stars is often larger than expected. The clumping explains this characteristic in the wind, increasing the mean density and hence the emission measure, making possible to understand the observed infrared, as well as the observed enhancement in the blue wing of the $H_\alpha$ line. In this study, we investigate the formation of these clumps a via thermal instability. The heat-loss function used, $H(T,n)$, includes physical processes such as: emission of (continuous and line) recombination radiation; resonance line emission excited by electron collisions; thermal bremsstrahlung; Compton heating and cooling; and damping of Alfv\'en waves. As a result of this heat-loss function we show the existence of two stable equilibrium regions. The stable equilibrium region at high temperature is the diffuse medium and at low temperature the clumps. Using this reasonable heat-loss function, we show that the two stable equilibrium regions can coexist over a narrow range of pressures describing the diffuse medium and the clumps.Comment: 21 pages (psfig.sty), 5 figures (included), ApJ accepted. Also available at http://www.iagusp.usp.br/preprints/preprint.htm

Tsunamis in Galaxy Clusters: Heating of Cool Cores by Acoustic Waves

Using an analytical model and numerical simulations, we show that acoustic waves generated by turbulent motion in intracluster medium effectively heat the central region of a so-called ``cooling flow'' cluster. We assume that the turbulence is generated by substructure motion in a cluster or cluster mergers. Our analytical model can reproduce observed density and temperature profiles of a few clusters. We also show that waves can transfer more energy from the outer region of a cluster than thermal conduction alone. Numerical simulations generally support the results of the analytical study.Comment: 18 pages, accepted for publication in Ap

Coupled spheroid and black-hole formation, and the multifrequency detectability of active galactic nuclei and submillimetre sources

We use a simple model of spheroid formation to explore the relationship between the creation of stars and dust in a massive proto galaxy and the growth of its central black hole. This model predicts that sub-mm luminosity peaks after only ~ 0.2 Gyr. However, without a very massive seed black hole, Eddington-limited growth means that a black hole mass of 10^9 solar masses, and hence very luminous AGN activity, cannot be produced until > 0.5 Gyr after the formation of the first massive stars in the halo. The model thus predicts a time-lag between the peak of sub-mm luminosity and AGN luminosity in a massive proto-elliptical of a few times 10^8 years. For a formation redshift z = 5, this means that powerful AGN activity is delayed until z = 3.5, by which time star formation in the host is 90% complete, and sub-mm luminosity has declined to ~ 25% of its peak value. This provides a natural explanation for why successful sub-mm detections of luminous radio galaxies are largely confined to z > 2.5. Conversely the model also predicts that while all high-redshift luminous sub-mm-selected sources should contain an active (and growing) black hole, the typical luminosity of the AGN in such objects is ~1000 times smaller than that of the most powerful AGN. This is consistent with the almost complete failure to detect sub-mm selected galaxies with existing X-ray surveys. Finally the model yields a black-hole:spheroid mass ratio which evolves rapidly in the first Gyr, but asymptotes to ~ 0.001-0.003 in agreement with results at low redshift. This ratio arises not because the AGN terminates star formation, but because fueling of the massive black hole is linked to the total mass of gas available for star formation in the host.Comment: Revised version accepted for publication in MNRAS. 10 pages with 8 figure

LIFE IN THE COSMIC CONTEXT. AN ASTROBIOLOGY COURSE AS AN EXPERIMENT IN TRANSDISCIPLINARITY

“Life in the Cosmic Context” (AGA0316) is\ud the astrobiology course offered by University\ud of S˜ao Paulo to undergraduate students of\ud science and humanities majors. The variety\ud of background of the population attending\ud AGA0316 and the broad scope of the addresssed\ud issues makes this course a laboratory\ud of transdisciplinarity.Resumo publicado no periódico: Revista Mexicana de Astronomía y Astrofísica. Serie de Conferencias, v. 44, p. 127, 2014