Variable Circumstellar Extinction in UX Ori Stars of Late Spectral Types: V695 Per

Context. A multiwavelength study of laboratory carbons with varying degrees of hydrogenation and sp2 hybridization is required to characterize the structure of the carbonaceous carriers of interstellar and circumstellar extinction. Aims. We study the spectral properties of carbonaceous dust analogs from the far-ultraviolet to the mid-infrared and correlate features in both spectral ranges to the aromatic/aliphatic degree. Methods. Analogs to carbonaceous interstellar dust encountered in various phases of the interstellar medium have been prepared in the laboratory. These are amorphous hydrogenated carbons (a-C:H), analogs to the diffuse interstellar medium component, and soot particles, analogs to the polyaromatic component. Thin films (d < 100 nm) have been measured in transmission in the vacuum-ultraviolet (VUV; 120–210 nm) within the atmospheric pressure experiment (APEX) chamber of the DISCO beam line at the SOLEIL synchrotron radiation facility. Spectra of these films were further measured through the UV-Vis (210 nm–1 μm) and in the mid-infrared (3–15 μm). Results. Tauc optical gaps, Eg, are derived from the visible spectra. The major spectral features are fitted through the VUV to the mid-infrared to obtain positions, full-widths at half maximum (FWHM), and integrated intensities. These are plotted against the position of the π-π∗ electronic transitions peak. Unidentified or overlapping features in the UV are identified by correlations with complementary infrared data. A correlation between the optical gap and position of the π-π∗ electronic transitions peak is found. The latter is also correlated to the position of the sp3 carbon defect band at ~8 μm, the aromatic C=C stretching mode position at ~6 μm, and the H/C ratio. Conclusions. Ultraviolet and infrared spectroscopy of structurally diverse carbon samples are used to constrain the nanostructural properties of carbon carriers of both circumstellar and interstellar extinction, such as the associated coherent lengths and the size of polyaromatic units. Our study suggests that carriers of the interstellar UV bump should exhibit infrared bands akin to the A/B classes of the aromatic infrared bands, while the circumstellar bump carriers should exhibit bands corresponding to the B/C classes.

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Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/sty3066 ◽

2018 ◽

Vol 483 (1) ◽

pp. 132-146 ◽

Cited By ~ 3

Author(s):

P P Petrov ◽

K N Grankin ◽

J F Gameiro ◽

S A Artemenko ◽

E V Babina ◽

...

Keyword(s):

T Tauri Stars ◽

Gas Flows ◽

Photometric Variability ◽

Outflow Velocity ◽

T Tauri ◽

Photometric Observations ◽

Accretion Model ◽

Circumstellar Extinction ◽

Magnetospheric Accretion

Abstract Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars, RY Tauri and SU Aurigae, with the aim to quantify the accretion and outflow dynamics at time-scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau, we observed a new effect: during events of enhanced outflow, the circumstellar extinction becomes lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time-scale of years. Periods of quiescence in the variability of the Hα profile were observed during the 2015–2016 period in RY Tau and during the 2016–2017 period in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and we discuss how the global stellar magnetic field can influence the long-term variations of the outflow activity.

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CI Camelopardalis: The first sgB[e]-high mass X-ray binary twenty years on: A supernova imposter in our own Galaxy?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834315 ◽

2019 ◽

Vol 622 ◽

pp. A93 ◽

Cited By ~ 4

Author(s):

E. S. Bartlett ◽

J. S. Clark ◽

I. Negueruela

Keyword(s):

Variable Mass ◽

Compact Object ◽

Small Population ◽

High Mass ◽

Circumstellar Envelope ◽

Local Conditions ◽

Single Star ◽

X Ray ◽

Circumstellar Extinction ◽

Binary Evolution

Context. The Galactic supergiant B[e] star CI Camelopardalis (CI Cam) was the first sgB[e] star detected during an X-ray outburst. The star brightened to ∼2 Crab in the X-ray regime (∼5 × 10−8 ergs cm−2 s−1 in the 2–25 keV range) within hours before decaying to a quiescent level in less than two weeks, clearly indicative of binarity. Since the outburst of CI Cam, several sgB[e] stars have been identified as X-ray overluminous for a single star (i.e. LX > 10−7 Lbol). This small population has recently expanded to include two ultra luminous X-ray sources (ULX), Holmberg II X-1 and NGC 300 ULX-1/supernova imposter SN2010da. Aims. Since the discovery of X-ray emission from CI Cam, there have been many developments in the field of massive binary evolution. In light of the recent inclusion of two ULXs in the population of X-ray bright sgB[e] stars, we revisit CI Cam to investigate its behaviour over several timescales and shed further light on the nature of the compact object in the system, its X-ray outburst in 1998 and the binary system parameters. Methods. We analysed archival XMM-Newton EPIC-pn spectra and light curves along with new data from Swift and NuSTAR. We also present high-resolution (R ∼ 85 000) Mercator/HERMES optical spectra, including a spectrum taken 1.02 days after our NuSTAR observation. Results. Despite being in quiescence, CI Cam is highly X-ray variable on timescales of days, both in terms of total integrated flux and spectral shape. We interpret these variations by invoking the presence of an accreting compact companion immersed in a dense, highly structured, aspherical circumstellar envelope. The differences in the accretion flux and circumstellar extinction represent either changes in this environment, triggered by variable mass loss from the star, or the local conditions to the accretor due to its orbital motion. We find no evidence for pulsations in the X-ray light curve. Conclusions. CI Cam has many similarities with SN2010da across mid-IR, optical and X-ray wavelengths suggesting that, subject to distance determination for CI Cam, if CI Cam was located in an external galaxy its 1998 outburst would have led to a classification as a supernova imposter.

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Non-LTE models of the accretion disks of UX Ori stars

Astrophysics ◽

10.1007/bf02700914 ◽

1999 ◽

Vol 42 (1) ◽

pp. 54-63 ◽

Cited By ~ 8

Author(s):

L. V. Tambovtseva ◽

V. P. Grinin ◽

O. V. Kozlova

Keyword(s):

Accretion Disks ◽

Ux Ori Stars

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Circumstellar dust and circumstellar extinction curves

Astrophysics and Space Science ◽

10.1007/bf00667849 ◽

1995 ◽

Vol 224 (1-2) ◽

pp. 223-226 ◽

Cited By ~ 2

Author(s):

N. V. Voshchinnikov ◽

F. J. Molster ◽

P. S. Th�

Keyword(s):

Circumstellar Dust ◽

Circumstellar Extinction

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Hydrodynamics of Young Binaries with Low-Mass Secondaries

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311028304 ◽

2011 ◽

Vol 7 (S282) ◽

pp. 521-524

Author(s):

Tatiana Demidova ◽

Vladimir Grinin ◽

Nataliya Sotnikova

Keyword(s):

Young Star ◽

Secondary Component ◽

Model Parameters ◽

Mass Ratio ◽

Cyclic Activity ◽

Orbit Plane ◽

Sph Method ◽

Circumstellar Extinction ◽

Low Mass

AbstractThe model of a young star with a low-mass secondary component (q = M2/M1 ≤ 0.1) accreting matter from a circumbinary (CB) disc is considered. It is assumed that the orbit and the CB disc can be coplanar and non-coplanar. The model parameters were varied within the following ranges: the component mass ratio q ranged from 0.1 to 0.003, the eccentricity e varied from 0 to 0.7, the inclination of the orbit plane to the CB disc ranged from 0 to 10 degrees, and the parameter that defines the viscosity of the system was also varied. A number of hydrodynamics models of such a system have been calculated by the SPH method and then the variations of the circumstellar extinction and phase brightness curves were determined. The calculated brightness curves differ in shape and amplitude and it depends on the model parameters and the orientation of the system relative to the observer. The results were used to analyze the cyclic activity of UX Ori type stars.

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Gaia DR2 study of Herbig Ae/Be stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832870 ◽

2018 ◽

Vol 620 ◽

pp. A128 ◽

Cited By ~ 33

Author(s):

M. Vioque ◽

R. D. Oudmaijer ◽

D. Baines ◽

I. Mendigutía ◽

R. Pérez-Martínez

Keyword(s):

Near Infrared ◽

Strong Support ◽

High Mass ◽

Be Stars ◽

Line Profiles ◽

Lower Mass ◽

Photometric Variability ◽

Ux Ori Stars ◽

The Difference ◽

Herbig Ae Stars

Aims. We use Gaia Data Release 2 (DR2) to place 252 Herbig Ae/Be stars in the Hertzsprung–Russell diagram and investigate their characteristics and properties. Methods. For all known Herbig Ae/Be stars with parallaxes in Gaia DR2, we collected their atmospheric parameters and photometric and extinction values from the literature. To these data we added near-infrared and mid-infrared photometry, and collected Hα emission line properties such as equivalent widths and line profiles, and their binarity status. In addition, we developed a photometric variability indicator from Gaia’s DR2 information. Results. We provide masses, ages, luminosities, distances, photometric variabilities and IR excesses homogeneously derived for the most complete sample of Herbig Ae/Be stars to date. We find that high-mass stars have a much smaller IR excess and have much lower optical variabilities compared to lower-mass stars, with the break at around 7 M⊙. Hα emission is generally correlated with IR excess, with the correlation being stronger for IR emission at wavelengths tracing the hot dust closest to the star. The variability indicator as developed by us shows that ∼25% of all Herbig Ae/Be stars are strongly variable. We observe that the strongly variable objects display doubly peaked Hα line profiles, indicating an edge-on disk. Conclusions. The fraction of strongly variable Herbig Ae stars is close to that found for A-type UX Ori stars. It had been suggested that this variability is in most cases due to asymmetric dusty disk structures seen edge-on. The observation here is in strong support of this hypothesis. Finally, the difference in dust properties occurs at 7 M⊙, while various properties traced at UV/optical wavelengths differ at a lower mass, 3 M⊙. The latter has been linked to different accretion mechanisms at work, whereas the differing IR properties and photometric variabilities are related to different or differently acting (dust-)disk-dispersal mechanisms.

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