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Studying the physical conditions structuring the young circumstellar disks is required for understanding the onset of planet formation. Of particular interest is the protoplanetary disk surrounding the Herbig star MWC480. The structure and properties of the circumstellar disk of MWC480 are studied by infrared interferometry and interpreted from a modeling approach. New observations are driving this study, in particular some recent Very Large Telescope Interferometer (VLTI)/MIDI data acquired in December 2013. Our one-component disk model could not reproduce simultaneously all our data: the Spectral Energy Distribution, the near-infrared Keck Interferometer data and the mid-infrared data obtained with the MIDI instrument. In order to explain all measurements, one possibility is to add an asymmetry in our one-component disk model with the assumption that the structure of the disk of MWC480 has not varied with time. Several scenarios are tested, and the one considering the presence of an azimuthal bright feature in the inner component of the disk model provides a better fit of the data. (In this study, we assumed that the size of the outer disk of MWC480 to be 20 au since most of the near and mid-IR emissions come from below 20 au. In our previous study (Jamialahmadi et al. 2015), we adopted an outer radius of 80 au, which is consistent with the value found by previous studies based on mm observations)., Comment: Accepted for publication in MNRAS, 12 pages, 9 figures, 4 tables

Dust trapping accelerates the coagulation of dust particles, and thus it represents an initial step toward the formation of planetesimals. We report $H$-band (1.6 um) linear polarimetric observations and 0.87 mm interferometric continuum observations toward a transitional disk around LkHa 330. As results, a pair of spiral arms were detected in the $H$-band emission and an asymmetric (potentially arm-like) structure was detected in the 0.87 mm continuum emission. We discuss the origin of the spiral arm and the asymmetric structure, and suggest that a massive unseen planet is the most plausible explanation. The possibility of dust trapping and grain growth causing the asymmetric structure was also investigated through the opacity index (beta) by plotting the observed SED slope between 0.87 mm from our SMA observation and 1.3 mm from literature. The results imply that grains are indistinguishable from ISM-like dust in the east side ($beta = 2.0 pm 0.5$), but much smaller in the west side $beta = 0.7^{+0.5}_{-0.4}$, indicating differential dust size distribution between the two sides of the disk. Combining the results of near-infrared and submillimeter observations, we conjecture that the spiral arms exist at the upper surface and an asymmetric structure resides in the disk interior. Future observations at centimeter wavelengths and differential polarization imaging in other bands (Y to K) with extreme AO imagers are required to understand how large dust grains form and to further explore the dust distribution in the disk., 10 pages, 4 figures, AJ accepted for publication

We present a survey of high dispersion UV and optical spectra of Herbig Ae/Be (HAeBe) and related stars. We nd accreting, circumstellar gas over the velocity range +100 to +400 km s 1 , and absorption proles similar to those seen toward Pic, in 36% of the 33 HAeBe stars with IUE data as well as in 3 non-emission B stars. We also nd evidence of accretion in 7 HAeBe stars with optical data only. Line prole variability appears ubiquitous. As a group, the stars with accreting gas signatures have higher v sini than the stars with outflowing material, and tend to exhibit large amplitude ( 1 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 Pic are not unique to that object, but instead are consistent with interpretation of Pic as a comparatively young A star with its associated circumstellar disk.

One of the key predictions of modeling from the IR excess of Herbig Ae stars is that for protoplanetary disks, where significant grain growth and settling has occurred, the dust disk has flattened to the point that it can be partially or largely shadowed by the innermost material at or near the dust sublimation radius. When the self-shadowing has already started, the outer disk is expected to be detected in scattered light only in the exceptional cases when the scale height of the dust disk at the sublimation radius is smaller than usual. High-contrast imaging combined with the IR spectral energy distribution allow us to measure the degree of flattening of the disk, as well as to determine the properties of the outer disk. We present polarimetric differential imaging in the H band obtained with Subaru/HiCIAO of one such system, MWC 480. The HiCIAO data were obtained at a historic minimum of the NIR excess. The disk is detected in scattered light from 0farcs2 to 1farcs0 (27.4-137 AU). Together with the marginal detection of the disk from 1998 February 24 by Hubble Space Telescope/NICMOS, our data constrain the opening half-angle for the disk to lie between 1fdg3 ≤θ ≤ 2fdg2. When compared with similar measures in CO for the gas disk from the literature, the dust disk subtends only ~30% of the gas disk scale height (H/R ~ 0.03). Such a dust disk is a factor of 5-7 flatter than transitional disks, which have structural signatures that giant planets have formed.

The O VIII phenomenon describes the occurrence of ultra-high ionization absorption lines of the CNO elements (e.g. O VIII, N VII, C VI, and even Ne X) in the optical spectra hot of DO WDs. This requires temperatures of almost 106 K. Since the first discovery of two such objects (Werner et al. 1995) we realized that 50% of all DO WDs are affected (Dreizler et al. 1995), hence it could be that all DO WDs experience this phenomenon at the beginning of the WD cooling sequence. The HeII profiles are symmetric, hence line formation occurs in hydrostatic layers. However, we cannot uniquely fit the unusually strong profiles with any model atmosphere, preventing precise parameter determinations. The optical high ionization CNO lines have pronounced blue wings, corresponding to outflow velocities of up to several thousand km/s. We stress that none of the objects was detected in the X-ray region. The inferred low X-ray luminosity confirms that we do not see absorption lines from super-hot photospheres, but that the high temperatures are possibly localized along shock fronts in the wind.

We discuss silicate emission profiles observed with the ISO SWS and ground-based IR observations in a population of intermittently embedded Herbig Ae/Be stars which are viewed edge-on to their polarimetrically identified dust and gas disks. The ISO SWS observations confirm the lack of a simple correlation between system age and the profile shape. Comparison with laboratory silicates suggests that much of the observed variation is due to different annealing histories of the grains.

Studies of the evolutionary precursors of β Pic have demonstrated that high velocity, accreting gas features are routinely detectable when the viewing geometry is similar to the β Pic system. We present a first exploration of the composition of the accreting gas toward 4 nearby, UV-luminous Herbig Ae/Be stars viewed through their circumstellar dust disks. We find that in addition to refractory materials, plausibly interpreted as sublimates of silicate grains, the accreting gas features in these stars contain carbon, mildly refractory species such as Zn II, and volatiles. Overall, the composition of the accreting gas is consistent with detection of the gaseous comae of star-grazing planetesimals of either cometary or carbonaceous chondritic composition.

The continua of BL Lacertae objects and other “blazars” are dominated by nonthermal emission that is variable and highly polarized at UV-radio wavelengths (Angel and Stockman 1980; Kollgaard 1994; Allen et al 1993). It is believed that this non-thermal emission is associated with the relativistic jets that are known to exist in these sources, but details of the jet structure and physics are still very uncertain. It is usually expected that the polarization behavior at optical and radio wavelengths should show little or no correlation, even if genuinely simultaneous measurements are compared. It is typically thought that the emission in these two wavebands originates in vastly different parts of the source, where the magnetic field geometries are likely to be quite different. In some inhomogeneous synchrotron source models for blazars, however, depending on the model parameters considered, the radio and UV-optical-IR (UVOIR) emission may be co-spatial (Ghisellini, Maraschi & Treves (1985)). It is thus of interest to search for correlations between the emission of blazars in the UVOIR and radio, to test such models. Our approach to doing this has been to compare simultaneous measurements of the optical and VLBI polarization characteristics of compact AGN. The polarization of the radiation is effectively used as a probe of the magnetic field structures in the regions where the emission at the two wavelengths arises.

We present the data and initial results from a combined Hubble Space Telescope (HST)/IUE/ground-based spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once every 2 days for a period of 74 days beginning on 1993 March 14. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations (both CCD imaging and aperture photometry), are reported for the period 1992 October-1993 September, although many of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution we describe the acquisition and reduction of all of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies.

One of the most promising approaches to unravelling the relationship between the optical and radio emission in AGN is to obtain nearly simultaneous optical and VLBI polarization data. We have obtained such data for five AGN (0735+178, OJ287, 1219+285, 3C 279, and BL Lac). These data suggest that there is a direct link between the optical and radio polarized emission, and that frequently the optical polarization of AGN is associated with the emergence of new VLBI components.

Visual and infrared photometry of strongly polarized QSOs (BL Lacertae objects) is reported. Spectral flux distributions of these objects are discussed in combination with results from earlier studies. With the exception of the well-resolved galaxies Mkn 421 and Mkn 501 only one object (1218 + 304) has a change in spectral index easily explained by the presence of an underlying galaxy. Six other sources appear to have either a break in their spectra near about 1 micron or a smoother general steepening of their spectra at shorter wavelengths. A spectral break at this wavelength may be attributed to a low flux of nonthermal radiation superimposed on a stellar energy distribution or by nonthermal electron energy losses.

New ultraviolet data are combined with optical data to investigate the wavelength-dependent extinction of the stars W46, W90, and W100 in the young galactic cluster NGC 2264. The observations of W90 confirm the existence of anomalous (circumstellar) dust extinction with a ratio of total to selective extinction, R greater than 7. This extinction is most easily explained by a graphite-silicate mixture with larger mean sizes than are present in the diffuse interstellar medium. For W46 and W100, the grains are likely to be gray, but the possibility of nongray extinction cannot be excluded because of uncertainties arising from the very small ultraviolet optical depths of the circumstellar dust.

Absolute fluxes over the wavelength range 1200-3200 A are presented for 13 normal early-type stars and 12 early-type stars known to have large IR excess; the data were obtained to study the UV spectral modifications produced by absorbing circumstellar dust particles. It is found that all the Be/shell stars whose spectral types are later than B6 exhibit greatly enhanced line absorption due to circumstellar Fe II. The circumstellar gaseous line absorption in stars cooler than B6 severely complicates the study of circumstellar dust absorption. However, those B and A stars that exhibit the circumstellar 9.7-micron emission feature have a very large increase in circumstellar absorption for 1800 A; such absorption is expected from circumstellar silicate particles.

The peculiar Be star HD 45677 was observed at low and high resolution by the IUE, and nearly simultaneous optical and IR observations were obtained with ground-based telescopes. These data were used to produce a spectral energy distribution extending from 0.12 to 12.6 microns in order to investigate the conversion of UV to IR radiation in the circumstellar dust shell. The high-resolution spectra indicate a spectral type of B2 in agreement with the optical classification.

Spectral measurements of the two BL Lac objects OQ 530 and ON 325 are presented. The measurements were taken at frequencies ranging from radio to ultraviolet. Both sources show spectral curvature between the infrared and ultraviolet frequencies. The intensity and spectral shape of OQ 530 vary, but the spectral shape of ON 325 appears to remain constant during intensity variability. A nonthermal theoretical model of jet emission is developed which incorporates both the spectral and time variability data. The model predicts that ON 325 radiates at X-ray frequencies with Compton radiation dominating over synchrotron emission. The angular size of the jet emission is predicted to be less than 0.1 milli-arcsec at high radio frequencies.

Low-resolution IUE data are used to explore the ultraviolet extinction toward the Wolf-Rayet star HD 193793 and to search for ultraviolet variability that might relate to the infrared variability. High-dispersion IUE observations are used to investigate the nature of the stellar wind of the star and to search for anomalies in the interstellar line spectrum that might be expected to be found toward a star that has recently formed a dust shell. Finally, the ultraviolet and new visual and infrared data are combined to investigate the full energy distribution of this unusual source. The energy distribution is found to extend from 0.12 to 12.5 microns, and the ultraviolet data suggest a normal WC-7 type star. A wind terminal speed of about 3000 km/s is implied by the data, as well as an E(B-V) value of 0.85. The dereddened ultraviolet to visual energy distribution is consistent with a star having effective temperature of about 43,000 K.

The authors report optical-infrared continuum observations of OJ 287 during its lowest recorded flux level. The spectrum was steeper than previously seen, but does not unambiguously show the presence of any underlying galaxy. It is suggested that this is primarily due to the object's still being too bright to make such a detection in this manner. The authors also report spectroscopic observations of OJ 287 showing the presence of Hα, Hβ, and [O III] emission lines. These lines confirm a redshift z = 0.306. The data are also used to compare the emitted luminosities in these lines to those of other active extragalactic objects. These lines are intrinsically underluminous compared to quasars of similar ionizing luminosities. The data are consistent with OJ 287 being deficient in gas compared to normal quasars or with the observed continuum flux having a Doppler factor of δ ≡ 4.

New observations of the ultraviolet spectrum of HD 44179 are reported. Absorption due to the CO molecule is present in the spectrum with NCO approximately 10 to the 18th power per sq cm. Emission due to either CO or a molecule containing C=C, C=N, C-C, and C-H bonds (or both) is also present.

Combined spectral energy distribution curves of six Ae/Be stars (BD+61 deg 154, AB Aur, V380 Ori, HD 259431, ZCMa, and BD+40 deg 4124), five peculiar shell stars (HD 31648, HD 45677, HD 50138, HD 163296, and HD 190073), and the peculiar central object in the Red Rectangle nebula (HD 44179), obtained with the IUE and a variety of ground-based optical and infrared telescope systems, are presented, covering the wavelength range of approximately 1300 A to 12.5 microns. The observations are reviewed, and include ultraviolet observations, low-resolution absolute visual spectrophotometry, moderate-resolution relative visual spectrophotometry, and infrared photometry. For most of the objects the ratio of the flux deficiency for lambda equals less than 1 micron to the flux excess for lambda equals greater than 1 micron is approximately unity. Only two of the objects (AB Aur and HD 163296) possess a strong emission feature at 9.7 microns, while one other (HD 31648) may have a weak 9.7 micron emission feature. Most of the objects have a broad, smooth, infrared emission curve resembling those seen in some WC stars. It is concluded that the dust surrounding these stars may be different from that seen in the diffuse interstellar medium.