Line Structure in the Spectrum of FU Orionis

New high-resolution spectra of FU Ori, obtained with the HIRES spectrograph at the Keck I telescope in 2003-2006, make it possible to compare the optical line profiles with those predicted by the self-luminous accretion disk model. A dependence of line width on excitation potential and on wavelength, expected for a Keplerian disk, is definitely not present in the optical region, nor is the line duplicity due to velocity splitting. The absorption lines observed in the optical region of FU Ori must originate in or near the central object, and here their profiles are shown to be those expected of a rigidly rotating object. They can be fitted by a rapidly rotating (v sin i = 70 km/s) high-luminosity G-type star having a large dark polar spot, with axis inclined toward the line of sight. Over these years, the radial velocity of FU Ori has remained constant to within +/-0.3 km/s, so there is no indication that the star is a spectroscopic binary. These results apply to the optical region ($\lambda< 8800$ \AA); more distant, cooler regions of the disk contribute in the infrared.Comment: 14 pages, 11 figures, accepted by A

Review of cometary spectra

The spectra of comet Kohoutek, comet Bradfield, and comet Mrkos are reviewed and compared in relation to stellar spectroscopy and evolution. The possibility of observing the absorption spectrum of a comet and direct measurement of Doppler shifts due to expansion or streaming motions in comets are considered along with the spectra of giant comets, such as, comet Minkowski, comet Baade, and comet Lovas. A speculative explanation for possible intrinsic abundance differences between comets is given

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

Profiles of Strong Permitted Lines in Classical T Tauri Stars

We present a spectral analysis of 30 T Tauri stars observed with the Hamilton echelle spectrograph over more than a decade. One goal is to test magnetospheric accretion model predictions. Observational evidence previously published supporting the model, such as emission line asymmetry and a high frequency of redshifted absorption components, are considered. We also discuss the relation between different line forming regions and search for good accretion rate indicators. In this work we confirm several important points of the models, such as the correlation between accretion and outflow, broad emission components that are mostly central or slightly blueshifted and only the occasional presence of redshifted absorption. We also show, however, that the broad emission components supposedly formed in the magnetospheric accretion flow only partially support the models. Unlike the predictions, they are sometimes redshifted, and are mostly found to be symmetric. The published theoretical profiles do not have a strong resemblance to our observed ones. We emphasize the need for accretion models to include a strong turbulent component before their profiles will match the observations. The effects of rotation, and the outflow components, will also be needed to complete the picture.Comment: 25 pages including 9 figures, 3 tables, accepted for publication in the Astronomical Journa

IRAS 05436-0007 and the Emergence of McNeil's Nebula

We present a study of McNeil's Nebula, a newly appeared reflection nebula in the L1630 cloud, together with photometry and spectroscopy of its source. New IR photometry compared to earlier 2MASS data shows that the star has brightened by about 3 magnitudes in the near-infrared, changing its location in a J-H/H-K diagram precisely along a reddening vector. A Gemini NIRI K-band spectrum shows strong CO-bandhead emission and Br-gamma is in emission, indicative of strong accretion. A Gemini GMOS optical spectrum shows only a red, heavily veiled continuum, with H-alpha strongly in emission and displaying a pronounced P Cygni profile, with an absorption trough reaching velocities up to 600 km s-1. This implies significant mass loss in a powerful wind. However, no evidence is found for any shocks, as commonly seen in collimated outflows from young stars. Apparently the eruption has dispersed a layer of extinction and this, together with the intrinsic brightening of the IRAS source, has allowed an earlier outflow cavity to be flooded with light, thus creating McNeil's Nebula.Comment: 9 pages, 5 figure

Radio Spectra and NVSS Maps of Decametric Sources

We constructed radio spectra for ~1400 UTR-2 sources and find that 46% of them have concave curvature. Inspection of NVSS maps of 700 UTR sources suggests that half of all UTR sources are either blends of two or more sources or have an ultra-steep spectrum (USS). The fraction of compact USS sources in UTR may be near 10%. Using NVSS and the Digitized Sky Survey(s) we expect to double the UTR optical identification rate from currently ~19%.Comment: 2 pages, no figures; to appear in Proc. "Observational Cosmology with the New Radio Surveys", eds. M. Bremer, N. Jackson & I. Perez-Fournon, Kluwer Acad. Pres

Radio and Optical Observations of the R Aquarii Jet

VLA observations at 6 cm and Lick Observatory optical plates of R Aquarii indicate the existence of a jetlike feature extending 7 -10 from the central star. A wide field map at 6 cm shows an unresolved compact radio source which lies close to the axis defined by the jet at a distance of ~ 3\u27 from R Aqr. Episodic mass transfer in this symbiotic variable could explain the erratic outbursts that R Aqr is known to undergo. Formation of an accretion disk and the accompanying radio-optical jet may characterize the observed outbursts in this system

Pre-Main Sequence variables in the VMR-D : identification of T Tauri-like accreting protostars through Spitzer-IRAC variability

We present a study of the infrared variability of young stellar objects by means of two Spitzer-IRAC images of the Vela Molecular Cloud D (VMR-D) obtained in observations separated in time by about six months. By using the same space-born IR instrumentation, this study eliminates all the unwanted effects usually unavoidable when comparing catalogs obtained from different instruments. The VMR-D map covers about 1.5 square deg. of a site where star formation is actively ongoing. We are interested in accreting pre-main sequence variables whose luminosity variations are due to intermittent events of disk accretion (i.e. active T Tauri stars and EXor type objects). The variable objects have been selected from a catalog of more than 170,000 sources detected at a S/N ratio > 5. We searched the sample of variables for ones whose photometric properties are close to those of known EXor's. These latter are monitored in a more systematic way than T Tauri stars and the mechanisms that regulate the observed phenomenology are exactly the same. Hence the modalities of the EXor behavior is adopted as driving criterium for selecting variables in general. We selected 19 bona fide candidates that constitute a well-defined sample of new variable targets for further investigation. Out of these, 10 sources present a Spitzer MIPS 24 micron counterpart, and have been classified as 3 Class I, 5 flat spectrum and 2 Class II objects, while the other 9 sources have spectral energy distribution compatible with phases older than Class I. This is consistent with what is known about the small sample of known EXor's, and suggests that the accretion flaring or EXor stage might come as a Class I/II transition. We present also new prescriptions that can be useful in future searches for accretion variables in large IR databases.Comment: 35 pages, 12 figures To appear in Ap