Search Publications
Quantifying the impact of variable BLR diffuse continuum contributions on measured continuum interband delays
Korista, K. T.; Goad, M. R.
We investigate the contribution of reprocessed continuum emission (1000-10 000 Å) originating in broad-line region (BLR) gas, the diffuse continuum (DC), to the wavelength-dependent continuum delays measured in AGN disc reverberation mapping experiments. Assuming a spherical BLR geometry, we adopt a Local Optimally emitting Cloud (LOC) model for t…
The spectral energy distributions of active galactic nuclei
Salvato, M.; Ricci, C.; Brown, M. J. I. +5 more
We present spectral energy distributions (SEDs) of 41 active galactic nuclei, derived from multiwavelength photometry and archival spectroscopy. All of the SEDs span at least 0.09 to 30 µm, but in some instances wavelength coverage extends into the X-ray, far-infrared, and radio. For some active galactic nuclei (AGNs) we have fitted the meas…
Spectral analysis of the extremely hot DA white dwarf PG 0948+534
Rauch, T.; Werner, K.; Reindl, N.
There is a striking paucity of hydrogen-rich (DA) white dwarfs (WDs) relative to their hydrogen-deficient (non-DA) counterparts at the very hot end of the WD cooling sequence. The three hottest known DAs (surface gravity log g ≥ 7.0) have effective temperatures around T_{eff} = 140 000 K, followed by only five objects in the range 104 000-120 000 …
Extreme resonance line profile variations in the ultraviolet spectra of NGC 1624-2: probing the giant magnetosphere of the most strongly magnetized known O-type star
Martins, F.; Owocki, S. P.; Wade, G. A. +12 more
In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent the first ultraviolet spectra of this archetypal object. We examine the variability of its wind-sensitive resonance lines, comparing it to that of other known magnetic O stars. In particular, the observed variations in the prof…
Fundamental parameters and evolutionary status of the magnetic chemically peculiar stars HD 188041 (V1291 Aquilae), HD 111133 (EP Virginis), and HD 204411: spectroscopy versus interferometry
Shulyak, D.; Ryabchikova, T.; Perraut, K. +4 more
The determination of fundamental parameters of stars is one of the main tasks of astrophysics. For magnetic chemically peculiar stars, this problem is complicated by the anomalous chemical composition of their atmospheres, which requires special analysis methods. We present the results of the effective temperature, surface gravity, abundance, and …
Ultraviolet and optical spectroscopy of AGB stars showing UV excess
Guerrero, Martín A.; Ortiz, Roberto; Costa, Roberto D. D.
We have examined ultraviolet (UV) and optical UB spectra of 20 UV-emitting Asymptotic Giant Branch (AGB) stars of various variability classes to study the intensity of the continuum and emission lines as a function of stellar visual magnitude to shed light on the origin of their UV emission. A significant fraction (60 per cent) of these stars show…
The enigmatic binary system HD 5980
Hillier, D. John; Morrell, Nidia; Nazé, Yaël +3 more
The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich Wolf-Rayet (WR) star. Since the eruption, the wind mass-loss rate has been declining while wind speeds have been steadily increasing. Observations obtained in 2014…
Hidden IR structures in NGC 40: signpost of an ancient born-again event
Guerrero, M. A.; Toalá, J. A.; Todt, H. +1 more
We present the analysis of infrared (IR) observations of the planetary nebula NGC 40 together with spectral analysis of its [WC]-type central star HD 826. Spitzer IRS observations were used to produce spectral maps centred at polycyclic aromatic hydrocarbons (PAH) bands and ionic transitions to compare their spatial distribution. The ionic lines s…
Investigating the origin of the spectral line profiles of the Hot Wolf-Rayet Star WR 2
Crowther, P. A.; Wade, G. A.; Chené, A. -N. +12 more
The hot WN star WR 2 (HD 6327) has been claimed to have many singular characteristics. To explain its unusually rounded and relatively weak emission line profiles, it has been proposed that WR 2 is rotating close to break-up with a magnetically confined wind. Alternatively, the line profiles could be explained by the dilution of WR 2's spectrum by…
Tiny grains shining bright in the gaps of Herbig Ae transitional discs
Monnier, John D.; Kraus, Stefan; Federrath, Christoph +7 more
This work presents a study of two Herbig Ae transitional discs, Oph IRS 48 and HD 169142; which both have reported rings in their dust density distributions. We use Keck-II/NIRC2 adaptive optics imaging observations in the L' filter (3.8 µm) to probe the regions of these discs inwards of {∼ }20 au from the star. We introduce our method for i…