We present new observations of the far-ultraviolet (FUV; 1100-2200 ) radiation field and the near-to mid-A IR (3-13.5 mm) spectral energy distribution (SED) of a sample of T Tauri stars selected on the basis of bright molecular disks (GM Aur, DM Tau, and LkCa 15). In each source we find evidence for Lya-induced H 2 fluorescence and an additional source of FUV continuum emission below 1700 . Comparison of the FUV spectrå A to a model of H 2 excitation suggests that the strong continuum emission is due to electron impact excitation of H 2 . The ultimate source of this excitation is likely X-ray irradiation that creates hot photoelectrons mixed in the molecular layer. Analysis of the SED of each object finds the presence of inner disk gaps with sizes of a few AU in each of these young (∼1 Myr) stellar systems. We propose that the presence of strong H 2 continuum emission and inner disk clearing are related by the increased penetration power of high-energy photons in gasrich regions with low grain opacity.

Infrared photometry and spectroscopy covering a time span of a quarter century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the -3exception of a major increase in emitted flux in a broad wavelength region centered near 3 µm in 2002. In contrast, HD 31648 has exhibited sporadic changes in the entire 3-13 µm region throughout this span of time. In both stars the changes in the 1-5 µm flux indicate structural changes in the region of the disk near the dust sublimation zone, possibly causing its distance from the star to vary with time. Repeated thermal cycling through this region will result in the preferential survival of large grains, and an increase in the degree of crystallinity. The variability observed in these objects has important consequences for the interpretation of other types of observations. For example, source variability will compromise models based on interferometry measurements unless the interferometry observations are accompanied by nearly-simultaneous photometric data.

We report on the results of a number of infrared spectra (0.8-2.5, 2.1-4.6, and 3-14 m) of V838 Monocerotis, taken from a short time after discovery in 2002 January to about 14 months later, in early 2003. The spectrum evolved dramatically, changing from a quasi-photospheric stellar spectrum with weak atomic emission lines (some with P Cygni profiles) to one showing a wide range of deep absorption features indicative of a cool, extended atmosphere with a circumstellar dust shell. The early spectra showed lines of s-process elements, such as Sr ii and Ba i. The later spectra showed absorption by gaseous H 2 O, CO, AlO, TiO, SiO, SO 2 , OH, VO, and SH, as well as a complex of emission near 10 m reminiscent of silicate emission, with a central absorbing feature at 10:3 m. Thus, V838 Mon appears to be oxygen-rich. A simple, spherically symmetric model of the system involving a central star with a two-component expanding circumstellar shell is presented that is able to explain the major molecular features and spectral energy distribution in the object's late stages. The derived shell mass and distance are 0.04 M and 9.2 kpc, respectively.

FS CMa stars form a group of objects with the B[e] phenomenon that were previously known as unclassified B[e] stars or B[e] stars with warm dust (B[e]WD) until recently. They exhibit strong emission-line spectra and strong IR excesses, most likely due to recently formed circumstellar dust. These properties have been suggested to be due to ongoing or recent rapid mass exchange in binary systems with hot primaries and various types of secondaries. The first paper of this series reported an analysis of the available information about previously known Galactic objects with the B[e] phenomenon, the initial selection of the FS CMa group objects, and a qualitative explanation of their properties. This paper reports the results of our new search for more FS CMa objects in the IRAS Point Source Catalog. We present new photometric criteria for identifying FS CMa stars as well as the first results of our observations of nine new FS CMa group members. With this addition, the FS CMa group has now 40 members, becoming the largest among the dust-forming hot star groups. We also present nine objects with no evidence for the B[e] phenomenon, but with newly discovered spectral line emission and/or strong IR excesses.

STIS white-light coronagraphic imaging has been carried out for 14 nearby, lightly reddened Herbig Ae stars, providing data on the environments and disks associated with these stars. No disks are detected in our data when the Herbig Ae star is accompanied by a stellar companion at r 2 00 . We find that the optical visibility of protoplanetary disks associated with Herbig Ae stars at r ! 50 70 AU from the star is correlated with the strength of the mid-IR PAH features, particularly 6.2 m. These features, like the FUV fluorescent H 2 emission, trace the presence of material sufficiently far above the disk midplane that it is directly illuminated by the star's FUV radiation. In contrast, measures of the bulk properties of the disk, including ongoing accretion activity, mass, and the submillimeter slope of the SED, do not correlate with the surface brightness of the optical nebulosity. Modelers have interpreted the appearance of the IR SED and the presence of emission from warm silicate grains at 10 m as a measure of geometrical shadowing by material in the disk near the dust sublimation radius of 0.5 AU. Geometrical shadowing sufficient to render a disk dark to distances as large as 500 AU from a star would require that the star be optically visible only if viewed essentially pole-on, in disagreement with our program star system inclinations. Rather than invoking shadowing to account for the optically dark disks, the correlation of the STIS detections with PAH emission features suggests a correlation with disk flaring and an anticorrelation with the degree of dust settling toward the midplane. If this correlation continues to lower levels, the STIS data suggest that improvements in coronagraph performance that suppress the residual scattered and diffracted stellar light by an additional factor of !10 should render the majority of disks associated with nearby Herbig Ae stars detectable.

Infrared spectroscopy of V2274 Cygni (=Nova Cygni 2001 No. 1) is presented for two widely separated epochs, 17 and 370 days after discovery. In addition to the Paschen and Brackett series of H i, the early-time spectrum shows strong emission lines of C i and N i, fluorescently excited lines of O i, and emission from the first overtone of carbon monoxide. Because the initial data were probably acquired no more than 18 days after outburst, CO molecule formation occurred remarkably quickly in the dense, cool, carbon and oxygen rich ejecta. Rapid formation was also seen in NQ Vul, V842 Cen, and V705 Cas, three other novae in which first-overtone CO emission has been detected. Formation of the CO molecule may occur chemically in a process that requires H 2 as a precursor or directly through radiative association. The overtone emission of V2274 Cyg indicates a temperature of $2500 K. The vibrational levels show no obvious departures from thermal equilibrium, which may indicate high optical depths in the fundamental. A large 13 C/ 12 C ratio (0:83 AE 0:3) is also indicated by the observations, consistent with the fast CNO burning expected in novae explosions. By the time of the second epoch observations, the emission lines of the neutral C, N, and O had disappeared. He i 10830 was the dominant emission feature in the spectrum. In addition to the hydrogen lines, recombination features of He ii were also strong. The common nebular lines of [S iii] were seen but only two coronal line, [S viii] 9911 and [Si vi] 19645, were detected. The CO emission had disappeared, but a strong thermal dust component was present. The interstellar reddening for the system was found to be E(BÀV Þ ¼ 1:3. This extinction, together with the absolute magnitude derived from the rate of decline of the light curve, suggest a distance of $10.8 kpc. This places V2274 Cyg well out of the Galactic plane. The small number of novae with spectroscopic detections of carbon monoxide all have prominent C i lines, moderate speed classes and ejection velocities, exhibit marked dust formation events, and result from an explosion on a CO-type white dwarf. Based on these similarities, the spectrum of V2274 is proposed as a likely near-infrared spectral template for other novae that display carbon monoxide emission.

Aims. We present optical and near-infrared spectral evolution of the Galactic nova V5114 Sgr (2004) during few months after the outburst. Methods. We use multi-band photometry and line intensities derived from spectroscopy to put constrains on the distance and the physical conditions of the ejecta of V5114 Sgr.Results. The nova showed a fast decline (t 2 11 days) and spectral features of Fe ii spectroscopic class. It reached M V = −8.7 ± 0.2 mag at maximum light, from which we derive a distance of 7700 ± 700 kpc and a distance from the galactic plane of about 800 pc. Hydrogen and oxygen mass of the ejecta are measured from emission lines, leading to ∼10 −6 and 10 −7 M , respectively. We compute the filling factor of the ejecta to be in the range 0.1-10 −3 . We found the value of the filling factor to decrease with time. The same is also observed in other novae, then giving support to the idea that nova shells are not homogeneously filled in, rather being the material clumped in relatively higher density blobs less affected by the general expanding motion of the ejecta.

We present a 0.9-2.5 m spectrum of V445 Puppis obtained about 3 years after maximum brightness. The spectrum shows thermal continuum emission and two narrow, structured emission lines: He i 1.0830 m and 2.0581 m. We interpret this to be emission from a hydrogen-deficient, helium-rich, low-temperature nebula surrounded by an optically thick dust shell, probably carbonaceous.