Catherine C. Venturini

Variability of Disk Emission in Pre-main-sequence and Related Stars. I. HD 31648 and HD 163296: Isolated Herbig Ae Stars Driving Herbig-Haro Flows

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 exception 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.

0.8-13 Micron Spectroscopy of V838 Monocerotis and a Model for Its Emission

Abstract : We report on the results of a number of infrared spectra (0.8-2.5, 2.1-4.6, and 3-14 microns) 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 H2O, CO, AlO, TiO, SiO, SO2, OH, VO, and SH, as well as a complex of emission near 10 microns reminiscent of silicate emission, with a central absorbing feature at 10:3 microns. 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 objects late stages. The derived shell mass and distance are 0.04 M(circle dot solar) and 9.2 kpc, respectively.

Near-Infrared Spectrophotometry and the CO Emission in V2274 Cygni (Nova Cygni 2001 No. 1)

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 H2 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 13C/12C ratio (0.83 ± 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 λ10830 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] λ9911 and [Si VI] λ19645, 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(B-V) = 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.

Near-Infrared Emission Lines of V723 Cassiopeiae (Nova Cassiopeiae 1995)

Near-infrared spectroscopy (0.8-2.5 μm) from two epochs is presented for the very slow nova V723 Cassiopeiae (=Nova Cassiopeiae 1995). Its bright, comparatively narrow emission lines (FWHM ~ 500 km s-1) make it ideal for determining wavelengths of unidentified emission lines that appear in the nebular/coronal stages of novae. We present wavelengths for 16 previously unobserved or unidentified features and search for identifications by looking for coincidences with known atomic transitions. For a candidate transition, the likely abundance of the parent ion is considered and then a collisional, fluorescent, or recombination process capable of exciting the feature is sought. Four of the lines are identified in this manner, all of them collisionally excited, forbidden transitions. One of these, [Ti VII] λ22050, is a new coronal line that de-excites directly to the ground state. Three other lines are associated with transitions from collisionally excited, low-lying, metastable levels of Fe+5. Of the remaining unidentified features, five, with wavelengths of 8926, 11110, 11900, 15545, and 20996 A, have been observed in other novae. Comparing the time development of these features with the [S VIII] λ9913 coronal line indicates that all have parent ions of lower excitation (<280 eV) than S+7.

Early spectral evolution of Nova Sagittarii 2004 (V5114 Sagittarii)

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 Fell 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.

Near-Infrared Spectroscopy of V1493 Aquilae and V4642 Sagittarii: Two Novae with Unusual Spectral Features

We present 0.8–2.5 μm spectroscopy of two novae with uncommon spectral features at different stages in their decline after outburst. Nova Aql 1999 No. 1 (V1493 Aql) was a very fast nova that initially exhibited a rapid decline in brightness that flattened by day 20 and actually reversed to show an unusual secondary peak. The near-infrared spectrum was observed during this secondary peak at 46 days after initial peak brightness. Blended low-excitation lines such as H I Brackett and Paschen and O I largely populated the spectrum, which also showed a strong continuum declining monotonically toward the red (1.4–2.5 μm). He II lines were just beginning to emerge. The overall spectral appearance was much more representative of the period a few days after outburst. A possible explanation for this, and the secondary peak in the visible light curve, is that the nova experienced a second period of mass loss, but of a more continuous rather than explosive nature. Nova Sgr 2000 (V4642 Sgr) was a moderately fast nova, observed 160 days after peak brightness. High-excitation lines, including coronal lines, were present in the spectrum. However, their profiles were distinctly different from those of the lower excitation lines. Also present were four emission lines that have only recently been detected in the spectra of novae and which remain unidentified.

Early-Time Infrared Spectra of the Type Ia Supernova 2000cx

We present 0.8 to 2.5 μm spectra of the Type Ia supernova 2000cx from 8 and 7 days before maximum light. The spectra consist of a continuum that closely follows that of a hot blackbody (25,000 K) upon which is superposed a small number of absorption and emission features. The most prominent absorption is due to the Mg II multiplet at 1.0926 μm (rest frame); the strongest emission feature is at ~1.25 μm and is probably due to Fe III. The broad Si II feature at ~1.65 μm, if present, is very weak. There is no evidence of the He I singlet at 2.0581 μm. Velocities in the Mg II feature extend to beyond 20,000 km s -1, indicating that carbon burning reached the outermost layers of the progenitor, and providing support for the delayed detonation models. The blackbody shape of the continuum beyond 0.9 μm is used to provide a limit on the in situ reddening of E(B-V) ≤ 0.1 mag. Given the probable uniformity of the early-time spectra of Type Ia supernovae (SNe Ia), this technique should be applicable to other SNe Ia. Multicolor light curves reported by other observers indicate that SN 2000cx was overluminous, suggesting a higher than usual production of 56Ni. This can account for the hotter than normal continuum and the generally higher excitation of the line features.

Toward Understanding the B[e] Phenomenon. II. New Galactic FS CMa Stars*

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

Time Development of Recurrent Nova CI Aquilae's 2000 Outburst between 0.8 and 2.5 MICRONS

We report 0.8–2.5 μm spectrophotometry of CI Aquilae at eight epochs between 2000 May 9 and 2001 June 2 UT, corresponding to approximately 3 and 391 days after peak brightness. Near peak brightness, the spectra showed emission lines that were characteristic of a low-excitation, nitrogen-rich shell. Within a few weeks, the spectra began to show higher excitation/ionization emission lines indicative of a harder illuminating source: the neutral metal lines faded, leaving only lines of H I, He I, and He II and the emerging coronal lines. A month after peak brightness, the [Ca VIII] coronal line at 2.3205 μm appeared and persisted until the last of our observations, on day +391. From the O I line ratios, we deduced a reddening of EB-V = 1.5 ± 0.1 and a visual extinction of AV = 4.6 ± 0.2. Along with the rate of decline from the light curve (t2), we derived a distance of 2.6 ± 1.3 kpc. The frequently observed unidentified novae lines were present in CI Aquilae along with a potentially new member of the group at 2.425 ± 0.002 μm.

Near-Infrared (0.8-2.5 Micron) Spectroscopy of Nova Sagittarius 1998 = V4633 Sagittarii

The 0.8–2.4 μm spectroscopy of the moderately fast Nova Sgr 1998 = V4633 Sgr, obtained approximately 525 and 850 days after peak brightness, revealed an expanding, hydrogen-deficient shell of medium excitation level that increased with time. The strongest lines were He I and He II and the coronal line of [Si VI] 1.9641 μm. Also prominent were the lines of H I, and coronal [Ca VIII] 2.3205 μm and [Si VII] 2.4807 μm. Other lines included the [S III] lines at 0.9069 and 0.9532 μm and the coronal lines of [Al IX] 2.0444 μm and [Ti VI] 1.7155 μm. Five lines that frequently appear in novae spectra remain unidentified: 0.8926, 1.1114, 1.1900, 1.5545, and 2.1000 ± 0.005 μm. All the observed lines were roughly 1800 km s-1 wide (FWHM), and no asymmetries or underlying plateaus were seen. The continuum was significantly shallower than a 1/λ4 blackbody emission (approximately stellar photosphere) and steepened with age.