S. Haro-Corzo

MIRROR AND POINT SYMMETRIES IN A BALLISTIC JET FROM A BINARY SYSTEM

Models of accretion disks around a star in a binary system predict that the disk will have a retrograde precession with a period a factor of ~10 times the orbital period. If the star+disk system ejects a bipolar outflow, this outflow will be subject to the effects of both the orbital motion and the precession. We present an analytic, ballistic model and a three-dimensional gasdynamical simulation of a bipolar outflow from a source in a circular orbit, and with a precessing outflow axis. We find that this combination results in a jet/counterjet system with a small spatial scale, reflection-symmetric spiral (resulting from the orbital motion) and a larger-scale, point-symmetric spiral (resulting from the longer period precession). These results provide interesting possibilities for modeling specific Herbig-Haro jets and bipolar planetary nebulae.

NANODIAMOND DUST AND THE FAR-ULTRAVIOLET QUASAR BREAK

We explore the possibility that the steepening observed shortward of 1000 A in the energy distribution of quasars may result from absorption by dust, being either intrinsic to the quasar environment or intergalactic. We find that a dust extinction curve consisting of nanodiamonds, composed of terrestrial cubic diamonds or with surface impurities as found in carbonaceous chondrite meteorites, such as Allende, is successful in reproducing the sharp break observed. The intergalactic dust model is partially successful in explaining the shape of the composite energy distribution but must be discarded in the end, as the amount of crystalline dust required is unreasonable and would imply an improbable fine-tuning among the dust formation processes. The alternative intrinsic dust model requires a mixture of both cubic diamonds and Allende nanodiamonds and provides a better fit of the UV break. The gas column densities implied are of the order 1020 cm-2, assuming solar metallicity for carbon and full depletion of carbon into dust. The absorption only occurs in the ultraviolet and is totally negligible in the visible. The minimum dust mass required is of the order ~0.003r M☉, where rpc is the distance in parsecs between the dust screen and the continuum source. The intrinsic dust model reproduces the flux rise observed around 660 A in key quasar spectra quite well. We present indirect evidence of a shallow continuum break near 670 A (18.5 eV), which would be intrinsic to the quasar continuum.

Energy Distribution of Individual Quasars from Far-Ultraviolet to X-Rays. I. Intrinsic Ultraviolet Hardness and Dust Opacities

Using Chandra and HST archival data, we have studied the individual SED of 11 quasars at redshifts 0.3 < z < 1.8. All UV spectra show a spectral break around 1100 ?. Five X-ray spectra showed the presence of a soft excess, and seven spectra showed an intrinsic absorption. We found that for most quasars a simple extrapolation of the far-UV power law into the X-ray domain generally lies below the X-ray data and that the big blue bump and the soft X-ray excess do not share a common physical origin. We explore the issue of whether the observed SED might be dust absorbed in the far- and near-UV. We fit the UV break, assuming a power law that is absorbed by cubic nanodiamond dust grains. We then explore the possibility of a universal SED (with a unique spectral index) by including further absorption from SMC-like extinction. Using this approach, satisfactory fits to the spectra can be obtained. The hydrogen column densities required by either nanodiamonds or amorphous dust models are all consistent, except for one object, with the columns deduced by our X-ray analysis, provided that the C depletion is ~0.6. Because dust absorption implies a flux recovery in the EUV (<700 ?), our modeling opens the possibility that the intrinsic quasar SED is much harder and more luminous in the EUV than inferred from the near-UV data, as required by photoionization models of the broad emission line region. We conclude that the intrinsic UV SED must undergo a sharp turnover before the X-ray domain.

STIS optical spectroscopy of the lobes of CRL 618

Context. Many proto-planetary nebulae show collimated structures sometimes showing multiple outflows. Aims. We present the results of new optical spectroscopic observations (both medium (with a dispersion of 0.56 A pixel −1 )a nd low (2.73 and 4.92 A pixel −1 for the G430L and G750L gratings) spectral resolution) of the lobes of the proto-planetary nebula CRL 618 obtained with the Space Telescope Imaging Spectrograph on board of the Hubble Space Telescope. Methods. We analyse the density structure and the excitation conditions of the lobes of CRL 618. The spectra obtained at medium spectral resolution (∼50 km s −1 ) allow us to quote the fraction of unscattered (intrinsic) Hα emission. We have also obtained dereddened emission line ratios of several features from the low spectral resolution spectra. Results. We find that most of the analysed line ratios are reproduced by planar shocks moving through a dense medium (with preshock densities ∼10 4 cm −3 ) with shock velocities from 30 to 40 km s −1 (except the [O III]/Hβ line ratios which require shock velocities of 80 to 90 km s −1 ). We find that the [S II]-weighted ionization fraction ranges from 0.015 to 0.06. The total densities derived from the electron density and the ionization fraction are ∼10 5 to 10 6 cm −3 . Conclusions. We conclude that the spectra of the lobes of CRL 618 can be margially reproduced by steady plane–parallel shock models for shock velocities which are significantly lower than the velocities at which the jet moves outwards (∼200 km s −1 ). These results are consistent with the predictions of a jet with a variable ejection velocity. The mirror-symmetry, the luminosity asymmetry between both lobes and the ejection velocity variability suggest that its central source may host a binary system.

SHAPING POINT- AND MIRROR-SYMMETRIC PROTOPLANETARY NEBULAE BY THE ORBITAL MOTION OF THE CENTRAL BINARY SYSTEM

We present three-dimensional hydrodynamical simulations of a jet launched from the secondary star of a binary system inside a protoplanetary nebula. The secondary star moves around the primary in a close eccentric orbit. From the gasdynamic simulations we compute synthetic [N II] lambda 6583 emission maps. Different jet axis inclinations with respect to the orbital plane, as well as different orientations of the flow with respect to the observer, are considered. For some parameter combinations, we obtain structures that show point- or mirror-symmetric morphologies depending on the orientation of the flow with respect to the observer. Furthermore, our models can explain some of the emission distribution asymmetries that are summarized in the classification given by Soker and Hadar.

Technique for Detecting Warm-Hot Intergalactic Gas in Quasar Ultraviolet Spectra

The ionizing spectral energy distribution of quasars exhibits a steepening of the distribution shortward of ~1200 ?. The change of the power-law index from approximately -1 (near-UV) to -2 (far-UV) has so far been interpreted as being intrinsic to quasars. We consider the possibility that the steepening may result from a tenuous absorption component that is anticorrelated with large mass overdensities. UV-sensitive satellites, whose detectors can extend down to 1000 ?, can set a useful limit to such an absorption component through the search for a flux increase in the window 1050-1190 ? (observer frame) with respect to an extrapolation of the continuum above 1230 ?. Since the recent Far Ultraviolet Spectroscopic Explorer and Hubble Space Telescope Space Telescope Imaging Spectrograph data do not show any obvious discontinuity in this region, this effectively rules out the possibility that intergalactic H I absorption is very important, and we conclude that most if not all of the steepening is intrinsic to quasars. A smaller flux discontinuity of order 1% cannot, however, be ruled out yet and would still be consistent with the warm-hot intergalactic component if it amounts to 30% of the baryonic mass, as predicted by some models of large scale structure formation, provided its temperature lies around 105.3 K.

Quasar 3C 298: a test-case for meteoritic nanodiamond 3.5 µm emission

Aims. We calculate the dust emission expected at 3.43 and 3.53 µm if meteoritic (i.e. hydrogenated) nanodiamonds are responsible for most of the far-UV break observed in quasars. Methods. We integrate the UV flux that hydrogenated nanodiamonds must absorb to reproduce the far-UV break. Based on laboratory spectra of H-terminated diamond surfaces, we analyse the radiative energy budget and derive theoretically the IR emission profiles expected for possible C-H surface stretch modes of the diamonds. Results. Using as test case a spectrum of 3C 298 provided by the Spitzer Observatory, we do not find evidence of these emission bands. Conclusions. While diamonds without surface adsorbates remain a viable candidate for explaining the far-UV break observed in quasars, hydrogenated nanodiamonds appear to be ruled out, as they would give rise to IR emission bands, which have not been observed so far.

Nanodiamond dust and the energy distribution of quasars

The spectral energy distribution of quasars shows a sharp steepening of the continuum shortward of ≃1100 A. The steepening could be a result of dust absorption. We present a dust extinction model which considers crystalline carbon grains and compare it with SMC-like dust extinction consisting of a mixture of silicate grains with graphite or amorphous carbon grains. We show that the sharp break seen in individual quasar spectra of intermediate redshift ∼1–2 can be reproduced by dust absorption provided the extinction curve consists of nanodiamonds, composed of terrestial cubic diamonds or of diamonds similar to the presolar nanodiamonds found in primitive meteorites. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Jets of the Proto-Planetary Nebula CRL 618

We present here the kinematic structure and the excitation conditions of the collimated outflows of the proto-planetary nebula CRL 618 based on high spatial resolution spectroscopy obtained with STIS onboard HST. The spectra obtained show a linear increase of the radial velocity with distance to the central source. We find that the emission line ratios observed in the clumpy lobes of CRL 618 are similar to high or low-excitation HH excitation class depending on the emission line ratio.