ALBERT

Description: The LBV characteristics of the new LBV candidate WRA 751 suggested by Hu et al. (1990) are studied in greater detail. A comparison is made with observational characteristics of the well-known LBVs Ag Car and HR Car using photometric and spectroscopic data of Hu et al. supplemented with an IUE spectrum and direct CCD images in H-alpha, blue, and red. It is found that the spectra of WRA 751 and HR Car discussed in this paper are similar to the minimum-phase spectrum of AG Car and therefore resemble the Of/WN 9 spectral type. The characteristics of the optical, near- and far-UV (IUE) spectra of the Fe II spectrum in these wavelength regions is due to continuum fluorescence. The H, He I, Fe II and forbidden Fe II emission lines are formed in different parts of the stars' envelopes, corresponding to their expanding velocities. It is concluded that WRA 751 has properties which fit well the LBV properties at minimum-brightness phase, and possesses circumstellar material with observational properties similar to those of the known LBVs AG Car and HR Car.

Description: We present additional photometric observations (Stromgren y filter) of the Herbig Ae Star HR 5999. This new set of data, composed of 282 data points covering April 1983 to August 1989, was used in conjunction with the 362 data points compiled by Baade and Stahl (1989). Our aim was to detect single or multiple periods in the integrated set of data spanning nearly 20 yr. Through the use of series analysis techniques, and by removing any linear component present in the raw data, we were able to detect weak peaks in the power spectra (in the order of intensity the strongest peaks are at 301 and 113 d) which were not self-evident in the phase diagrams. The overall picture of the data shows a small linear component, which is more noticeable in the new set of data, indicating that the recent maxima appear brighter. By a detailed analysis of the full light curve we were able to detect the presence of well-defined 'pulses' or bursts. Further Gaussian fits of these bursts indicated that the pulses are relatively rapid, of the order of 10 d, with some of them being closely spaced. No periodicity was found for the pulses. A possible explanation of these aperiodic outbursts is that they detect a flow of matter accompanied by magnetic field disturbances originated from the interior of the star, unlike those originating externally such as binary perturbations, which tend to be periodic.

Description: The newly discovered hot-emission line star, HD 147196 in the Rho Oph dark cloud region was observed spectroscopically and photometrically and high and low resolution IUE spectra were obtained. The finding of Irvine (1990) that this relatively bright star show its H-alpha-line in emission is confirmed. Previous H-alpha-surveys of the Rho Oph star-forming region did not detect HD 147196 as an H-alpha-emission star, meaning that it must recently be very active and has perhaps transformed itself from a B-type star at shell phase to a Be-phase. The Mg II h + k resonance lines are in absorption and they appear to be interstellar in nature, which means that either the abundance of Mg in the extended atmosphere of the star is low or that the shell is not extended enough to produce emission lines of Mg II. Photometric observations of this B8 V type star do not show any variations during at least the years covered by our monitoring or any excess of NIR radiation in its spectral energy distribution up to the M-passband at 4.8 microns.

Description: The photometric behavior of the Herbig Ae star V351 Ori was investigated combining data from the literature with new photometry. It is shown that this object changed from a Herbig Ae star with strong photometric variations, due to extinction by circumstellar dust clouds, to that of an almost non-variable star. Such a behavior is not unique; it has been found also in the star BN Ori. This suggests that such transitions as well as the opposite must occur quite often during the evolution of these intermediate mass stars towards the main-sequence. A provisional model to explain V351 Ori's behavior, in which it is assumed that a temporarily strong accretion of matter onto the star took place, is proposed.

Description: Results are presened on spectroscopic observations (carried out with the ESO 1.52-m telescope at La Silla, Chile) and measurements made by the Infrared Astronomical Satellite on the star WRA 751. It is estimated that the T(eff) of this star is 30,000 K and its E(B-V) is 1.8 mag. Comparison with evolutionary tracks of Maeder and Meynet (1980) indicates that WRA 751 is located in the region of luminous blue variables at a lower limit of the initial mass of about 50 solar masses. Its other physical characteristics, such as the light variability, strong Fe II lines, and the extinction-free spectral energy distribution, suggest that WRA 751 is a candidate for a new luminous blue variable.

Description: We present a survey of high dispersion UV and optical spectra of Herbig Ae/Be (HAeBe) and related stars. We find accreting, circumstellar gas over the velocity range +100 to +400 km/s, and absorption profiles similar to those seen toward Beta Pic, in 36% of the 33 HAeBe stars with IUE data as well as in 3 non-emission B stars. We also find evidence of accretion in 7 HAeBe stars with optical data only. Line profile variability appears ubiquitous. As a group, the stars with accreting gas signatures have higher v sin i than the stars with outflowing material, and tend to exhibit large amplitude (greater than or equal to 1(sup m)) optical light variations. All of the program stars with polarimetric variations that are anti-correlated with the optical light, previously interpreted as the signature of a dust disk viewed close to equator-on, also show spectral signatures of accreting gas. These data imply that accretion activity in HAeBe stars is preferentially observed when the line of sight transits the circumstellar dust disk. Our data imply that the spectroscopic signatures of accreting circumstellar material seen in Beta Pic are not unique to that object, but instead are consistent with interpretation of Beta Pic as a comparatively young A star with its associated circumstellar disk.

Description: Some preliminary results of a study of extreme emission line objects (EELOs) are presented. These stars are selected from H alpha emission line stars having a strong IR excess. The study is based on multiwavelength photometric and spectroscopic observations. Special attention is paid to the detailed study of the correlation between spectroscopic and photometric variations, which indicate the activity of the star. The ultraviolet and infrared extinction characteristics of the circumstellar material are given special attention.

Description: The IUE spectra of HR 5999 and BN Ori were analyzed, showing strong emission lines of C II, C IV, O I, and Si IV (also Mg II in HR 5999), indicating the presence of chromospheres and transition regions around these high mass premain sequence (PMS) stars. Infrared, optical, and ultraviolet observations show that BN Ori has a spectral type of FO-2 IIIe, a bolometric luminosity of 36 L, age 1.5 million yr, and mass 2 to 2.5 solar mass. As HR 5999 fades, the ratio of total to selective absorption increases indicating the appearance of larger grains or changes in grain alignment. Emission measure distributions are used to investigate the atmospheric structure of the stars. As HR 5999 fades the emission measure distribution rises systematically and the inferred transition region pressures increase. The transition region and chromospheric radiative losses are large and imply input mechanical energy fluxes similar to those of lower mass PMS stars.

Description: Analysis of IUE high- and low-dispersion spectra of the young Herbig Ae star HR 5999 (HD 144668) covering 1978-1992 revealed dramatic changes in the Mg II h and k (2795.5, 2802.7 A) emission profiles, changes in the column density and distribution in radial velocity of accreting gas, and flux in the Ly(alpha), O I, and C IV emission lines, which are correlated with the UV excess luminosity. Variability in the spectral type inferred from the UV spectral energy distribution, ranging from A5 IV-III in high state to A7 III in the low state, was also observed. The trend of earlier inferred spectral type with decreasing wavelength and with increasing UV continuum flux has previously been noted as a signature of accretion disks in lower mass pre-main sequence stars (PMS) and in systems undergoing FU Orionis-type outbursts. Our data represent the first detection of similar phenomena in an intermediate mass (M greater than or equal to 2 solar mass) PMS star. Recent IUE spectra show gas accreting toward the star with velocities as high as plus 300 km/s, much as is seen toward beta Pic, and suggest that we also view this system through the debris disk. The absence of UV lines with the rotational broadening expected given the optical data (A7 IV, V sini=180 plus or minus 20 km/s for this system) also suggests that most of the UV light originates in the disk, even in the low continuum state. The dramatic variability in the column density of accreting gas, is consistent with clumpy accretion, such as has been observed toward beta Pic, is a hallmark of accretion onto young stars, and is not restricted to the clearing phase, since detectable amounts of accretion are present for stars with 0.5 Myr less than t(sub age) less than 2.8 Myr. The implications for models of beta Pic and similar systems are briefly discussed.

Description: We report detection of high velocity, accreting gas toward the Be star with IR excess and bipolar nebula, HD 45677. High velocity (+200 to +400 km/s), variable column density gas is visible in all IUE spectra from 1979-1992 in transitions of Si II, C II, Al III, Fe III, Si IV, and C IV. Low-velocity absorption profiles from low oscillator-strength transitions of Si II, Fe II, and Zn II exhibit double-peaked absorption profiles similar to those previously reported in optical spectra of FU Orionis objects. The UV absorption data, together with previously reported analyses of the IR excess and polarization of this object, suggest that HD 45677 is a massive, Herbig Be star with an actively accreting circumstellar, proto-planetary disk.