The Mid-infrared Fine-structure Lines of Neon as an Indicator of Star For mation Rate in Galaxies

The fine-structure lines of singly ([Ne II] 12.8 micron) and doubly ([Ne III] 15.6 micron) ionized neon are among the most prominent features in the mid-infrared spectra of star-forming regions, and have the potential to be a powerful new indicator of the star formation rate in galaxies. Using a sample of star-forming galaxies with measurements of the fine-structure lines available from the literature, we show that the sum of the [Ne II] and [Ne III] luminosities obeys a tight, linear correlation with the total infrared luminosity, over 5 orders of magnitude in luminosity. We discuss the formation of the lines and their relation with the Lyman continuum luminosity. A simple calibration between star formation rate and the [Ne II]+[Ne III] luminosity is presented.Comment: To appear in ApJ. 8 page

Modeling RR Tel through the Evolution of the Spectra

We investigate the evolution of RR Tel after the outburst by fitting the emission spectra in two epochs. The first one (1978) is characterized by large fluctuations in the light curve and the second one (1993) by the slow fading trend. In the frame of a colliding wind model two shocks are present: the reverse shock propagates in the direction of the white dwarf and the other one expands towards or beyond the giant. The results of our modeling show that in 1993 the expanding shock has overcome the system and is propagating in the nearby ISM. The large fluctuations observed in the 1978 light curve result from line intensity rather than from continuum variation. These variations are explained by fragmentation of matter at the time of head-on collision of the winds from the two stars. A high velocity (500 km/s) wind component is revealed from the fit of the SED of the continuum in the X-ray range in 1978, but is quite unobservable in the line profiles. The geometrical thickness of the emitting clumps is the critical parameter which can explain the short time scale variabilities of the spectrum and the trend of slow line intensity decrease.Comment: 26 pages, LaTeX (including 5 Tables) + 6 PostScript figures. To appear in "The Astrophysical Journal

Illumination in symbiotic binary stars: Non-LTE photoionization models. II. Wind case

We describe a non-LTE photoionization code to calculate the wind structure and emergent spectrum of a red giant wind illuminated by the hot component of a symbiotic binary system. We consider spherically symmetric winds with several different velocity and temperature laws and derive predicted line fluxes as a function of the red giant mass loss rate, \mdot. Our models generally match observations of the symbiotic stars EG And and AG Peg for \mdot about 10^{-8} \msunyr to 10^{-7} \msunyr. The optically thick cross- section of the red giant wind as viewed from the hot component is a crucial parameter in these models. Winds with cross-sections of 2--3 red giant radii reproduce the observed fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models favor winds with acceleration regions that either lie far from the red giant photosphere or extend for 2--3 red giant radii.Comment: 51 pages, LaTeX including three tables, requires 15 Encapsulated Postscript figures, to appear in Ap

3D simulations of RS Oph: from accretion to nova blast

RS Ophiuchi is a recurrent nova with a period of about 22 years, consisting of a wind accreting binary system with a white dwarf (WD) very close to the Chandrasekhar limit and a red giant star (RG). The system is considered a prime candidate to evolve into an SNIa. We present a 3D hydrodynamic simulation of the quiescent accretion and the subsequent explosive phase. The computed circumstellar mass distribution in the quiescent phase is highly structured with a mass enhancement in the orbital plane of about a factor of 2 as compared to the poleward directions. The simulated nova remnant evolves aspherically, propagating faster toward the poles. The shock velocities derived from the simulations are in agreement with those derived from observations. For v_RG = 20 km/s and for nearly isothermal flows, we derive a mass transfer rate to the WD of 10% of the mass loss of the RG. For an RG mass loss of 10^{-7} solar masses per year, we found the orbit of the system to decay by 3% per million years. With the derived mass transfer rate, multi-cycle nova models provide a qualitatively correct recurrence time, amplitude, and fastness of the nova. Our simulations provide, along with the observations and nova models, the third ingredient for a deeper understanding of the recurrent novae of the RS Oph type. In combination with recent multi-cycle nova models, our results suggests that the WD in RS Oph will increase in mass. Several speculative outcomes then seem plausible. The WD may reach the Chandrasekhar limit and explode as an SN Ia. Alternatively, the mass loss of the RG could result in a smaller Roche volume, a common envelope phase, and a narrow WD+WD system. Angular momentum loss due to graviational wave emission could trigger the merger of the two WDs and - perhaps - an SN Ia via the double degenerate scenario.Comment: Accepted by Astronomy & Astrophysics Letters, 4 pages, 5 figures; Version with high resolution figures and movie can be found at http://www.astro.phys.ethz.ch/staff/folini/private/research/rsoph/rsoph.htm

Signature of Electron Capture in Iron-Rich Ejecta of SN 2003du

Late-time near-infrared and optical spectra are presented for the normal-bright SN2003du. At about 300 days after the explosion, the emission profiles of well isolated [FeII] lines (in particular that of the strong 1.644mu feature) trace out the global kinematic distribution of radioactive material in the expanding. In SN2003du, the 1.644 mu [FeII] line shows a flat-topped, profile, indicative of a thick but hollow-centered expanding shell, rather than a strongly-peaked profile that would be expected from a ``center-filled'' distribution.Based on detailed models for exploding Chandrasekhar mass white dwarfs, we show that the feature is consistent with spherical explosion models.Our model predicts central region of non-radioactive electron-capture elements up to 2500--3000km/s as a consequence of burning under high density, and an extended region of 56Ni up to 9,000--10,000km/s. Furthermore our analysis indicates that the 1.644mu [FeII] profile is not consistent with strong mixing between the regions of electron- capture isotopes and the 56Ni layers as is predicted by detailed 3D models for nuclear deflagration fronts. We discuss the possibility that the flat-topped profile could be produced as a result of an infrared catastrophe and conclude that such an explanation is unlikely. We put our results in context to other SNeIa and briefly discuss the implications of our result for the use of SNe Ia as cosmological standard candles.Comment: 12 pages + 8 figures, ApJ (in press, Dec. 20, 2004) For high resolution figures send E-mail to [email protected]

The Unusual Object IC 2144/MWC 778

IC 2144 is a small reflection nebula located in the zone of avoidance near the Galactic anticenter. It has been investigated here largely on the basis of Keck/HIRES optical spectroscopy (R ~ 48,000) and a SpeX spectrogram in the near-IR (R = 2000) obtained at the NASA IRTF. The only star in the nebula that is obvious in the optical or near-IR is the peculiar emission-line object MWC 778 (V = 12.8), which resembles a T Tauri star in some respects. What appear to be F- or G-type absorption features are detectable in its optical region under the very complex emission line spectrum; their radial velocity agrees with the CO velocity of the larger cloud in which IC 2144 is embedded. There are significant differences between the spectrum of the brightest area of the nebula and of MWC 778, the presumed illuminator, an issue discussed in some detail. The distance of IC 2144 is inferred to be about 1.0 kpc by reference to other star-forming regions in the vicinity. The extinction is large, as demonstrated by [Fe II] emission line ratios in the near-IR and by the strength of the diffuse interstellar band spectrum; a provisional value of A_V of 3.0 mag was assumed. The SED of MWC 778 rises steeply beyond about 1 $\mu$m, with a slope characteristic of a Class I source. Integration of the flux distribution leads to an IR luminosity of about 510 L_solar. If MWC 778 is indeed a F- or G-type pre--main-sequence star several magnitudes above the ZAMS, a population of faint emission Halpha stars would be expected in the vicinity. Such a search, like other investigations that are recommended in this paper, has yet to be carried out.Comment: 36 pages, 13 figures, accepted by A

Multiwavelength evidence for a 15-year periodic activity in the symbiotic nova V1016 Cygni

The ~15.1 years period found in the long-term UBV photoelectric and photographic photometry of the symbiotic nova V1016 Cyg is detected also in the (J-K) colour index and in the UV continuum and emission line fluxes from IUE and HUT spectra. It could be interpreted either as the effect of recurrent enhanced mass loss episodes from the Mira type variable companion to a hot component along its ultra-wide orbit (proposed from recent HST observations) or the true orbital period of the inner, unresolved binary of a triple system. A 410-day delay of the maximum of UV emission lines fluxes with respect to the maximum of continuum was found. The pulsation period of the Mira type variable was improved to 474+/-6 days.Comment: 7 pages, 7 PostScript figures. Accepted for pubblication in A&

Star Formation in M51 Triggered by Galaxy Interaction

We have mapped the inner 360'' regions of M51 in the 158micron [CII] line at 55'' spatial resolution using the Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO). The emission is peaked at the nucleus, but is detectable over the entire region mapped, which covers much of the optical disk of the galaxy. There are also two strong secondary peaks at ~43% to 70% of the nuclear value located roughly 120'' to the north-east, and south-west of the nucleus. These secondary peaks are at the same distance from the nucleus as the corotation radius of the density wave pattern. The density wave also terminates at this location, and the outlying spiral structure is attributed to material clumping due to the interaction between M51 and NGC5195. This orbit crowding results in cloud-cloud collisions, stimulating star formation, that we see as enhanced [CII] line emission. The [CII] emission at the peaks originates mainly from photodissociation regions (PDRs) formed on the surfaces of molecular clouds that are exposed to OB starlight, so that these [CII] peaks trace star formation peaks in M51. The total mass of [CII] emitting photodissociated gas is ~2.6x10^{8} M_{sun}, or about 2% of the molecular gas as estimated from its CO(1-0) line emission. At the peak [CII] positions, the PDR gas mass to total gas mass fraction is somewhat higher, 3-17%, and at the secondary peaks the mass fraction of the [CII] emitting photodissociated gas can be as high as 72% of the molecular mass.... (continued)Comment: 14 pages, 6 figures, Accepted in ApJ (for higher resolution figures contact the author

Silicates in D-type symbiotic stars: an ISO overview

We investigate the IR spectral features of a sample of D-type symbiotic stars. Analyzing unexploited ISO-SWS data, deriving the basic observational parameters of dust bands and comparing them with respect to those observed in other astronomical sources, we try to highlight the effect of environment on grain chemistry and physic. We find strong amorphous silicate emission bands at 10 micron and 18 micron in a large fraction of the sample. The analysis of the 10 micron band, along with a direct comparison with several astronomical sources, reveals that silicate dust in symbiotic stars shows features between the characteristic circumstellar environments and the interstellar medium. This indicates an increasing reprocessing of grains in relation to specific symbiotic behavior of the objects. A correlation between the central wavelength of the 10 and 18 micron dust bands is found. By the modeling of IR spectral lines we investigate also dust grains conditions within the shocked nebulae. Both the unusual depletion values and the high sputtering efficiency might be explained by the formation of SiO moleculae, which are known to be a very reliable shock tracer. We conclude that the signature of dust chemical disturbance due to symbiotic activity should be looked for in the outer, circumbinary, expanding shells where the environmental conditions for grain processing might be achieved. Symbiotic stars are thus attractive targets for new mid-infrared and mm observations.Comment: 24 pages, 6 figures, 5 tables - to be published in A

The Atomic Physics Underlying the Spectroscopic Analysis of Massive Stars and Supernovae

We have developed a radiative transfer code, CMFGEN, which allows us to model the spectra of massive stars and supernovae. Using CMFGEN we can derive fundamental parameters such as effective temperatures and surface gravities, derive abundances, and place constraints on stellar wind properties. The last of these is important since all massive stars are losing mass via a stellar wind that is driven from the star by radiation pressure, and this mass loss can substantially influence the spectral appearance and evolution of the star. Recently we have extended CMFGEN to allow us to undertake time-dependent radiative transfer calculations of supernovae. Such calculations will be used to place constraints on the supernova progenitor, to place constraints on the supernova explosion and nucleosynthesis, and to derive distances using a physical approach called the "Expanding Photosphere Method". We describe the assumptions underlying the code and the atomic processes involved. A crucial ingredient in the code is the atomic data. For the modeling we require accurate transition wavelengths, oscillator strengths, photoionization cross-sections, collision strengths, autoionization rates, and charge exchange rates for virtually all species up to, and including, cobalt. Presently, the available atomic data varies substantially in both quantity and quality.Comment: 8 pages, 2 figures, Accepted for publication in Astrophysics & Space Scienc