scholarly journals Dipper-like variability of the Gaia alerted young star V555 Ori

2021 ◽  
Vol 504 (1) ◽  
pp. 185-198
Author(s):  
Zsófia Nagy ◽  
Elza Szegedi-Elek ◽  
Péter Ábrahám ◽  
Ágnes Kóspál ◽  
Attila Bódi ◽  
...  
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Accretion Rate ◽  
Young Star ◽  
Short Term ◽  
T Tauri ◽  
Periodic Behaviour ◽  
Optical Wavelengths ◽  
Optical Flux

ABSTRACT V555 Ori is a T Tauri star, whose 1.5 mag brightening was published as a Gaia science alert in 2017. We carried out optical and near-infrared (NIR) photometric, and optical spectroscopic observations to understand the light variations. The light curves show that V555 Ori was faint before 2017, entered a high state for about a year, and returned to the faint state by mid-2018. In addition to the long-term flux evolution, quasi-periodic brightness oscillations were also evident, with a period of about 5 d. At optical wavelengths both the long-term and short-term variations exhibited colourless changes, while in the NIR they were consistent with changing extinction. We explain the brightness variations as the consequence of changing extinction. The object has a low accretion rate whose variation in itself would not be enough to reproduce the optical flux changes. This behaviour makes V555 Ori similar to the pre-main sequence star AA Tau, where the light changes are interpreted as periodic eclipses of the star by a rotating inner disc warp. The brightness maximum of V555 Ori was a moderately obscured (AV = 2.3 mag) state, while the extinction in the low state was AV = 6.4 mag. We found that while the Gaia alert hinted at an accretion burst, V555 Ori is a standard dipper, similar to the prototype AA Tau. However, unlike in AA Tau, the periodic behaviour was also detectable in the faint phase, implying that the inner disc warp remained stable in both the high and low states of the system.

scholarly journals Variability of young stellar objects in the star-forming region Pelican Nebula

2019 ◽  
Vol 627 ◽  
pp. A135 ◽  
Author(s):  
A. Bhardwaj ◽  
N. Panwar ◽  
G. J. Herczeg ◽  
W. P. Chen ◽  
H. P. Singh
Keyword(s):  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Main Sequence Stars ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Optical Wavelengths

Context. Pre-main-sequence variability characteristics can be used to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. The photometric variability of pre-main-sequence stars is studied at optical wavelengths to explore star–disk interactions, accretion, spots, and other physical mechanisms associated with young stellar objects. Methods. We observed a field of 16′ × 16′ in the star-forming region Pelican Nebula (IC 5070) at BVRI wavelengths for 90 nights spread over one year in 2012−2013. More than 250 epochs in the VRI bands are used to identify and classify variables up to V ∼ 21 mag. Their physical association with the cluster IC 5070 is established based on the parallaxes and proper motions from the Gaia second data release (DR2). Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalog of optical time-series photometry with periods, mean magnitudes, and classifications for 95 variable stars including 67 pre-main-sequence variables towards star-forming region IC 5070. The pre-main-sequence variables are further classified as candidate classical T Tauri and weak-line T Tauri stars based on their light curve variations and the locations on the color-color and color-magnitude diagrams using optical and infrared data together with Gaia DR2 astrometry. Classical T Tauri stars display variability amplitudes up to three times the maximum fluctuation in disk-free weak-line T Tauri stars, which show strong periodic variations. Short-term variability is missed in our photometry within single nights. Several classical T Tauri stars display long-lasting (≥10 days) single or multiple fading and brightening events of up to two magnitudes at optical wavelengths. The typical mass and age of the pre-main-sequence variables from the isochrone fitting and spectral energy distributions are estimated to be ≤1 M⊙ and ∼2 Myr, respectively. We do not find any correlation between the optical amplitudes or periods with the physical parameters (mass and age) of pre-main-sequence stars. Conclusions. The low-mass pre-main-sequence stars in the Pelican Nebula region display distinct variability and color trends and nearly 30% of the variables exhibit strong periodic signatures attributed to cold spot modulations. In the case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable on a timescale of one year.

scholarly journals Exploring the dimming event of RW Aurigae A through multi-epoch VLT/X-shooter spectroscopy

2019 ◽  
Vol 625 ◽  
pp. A49 ◽  
Author(s):  
M. Koutoulaki ◽  
S. Facchini ◽  
C. F. Manara ◽  
A. Natta ◽  
R. Garcia Lopez ◽  
...  
Keyword(s):  
Energy Distribution ◽  
Physical Properties ◽  
Near Infrared ◽  
Accretion Rate ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Infrared Excess ◽  
Mass Accretion Rate ◽  
Near Ir ◽  
T Tauri

Context. RW Aur A is a classical T Tauri star that has suddenly undergone three major dimming events since 2010. The reason for these dimming events is still not clear. Aims. We aim to understand the dimming properties, examine accretion variability, and derive the physical properties of the inner disc traced by the CO ro-vibrational emission at near-infrared wavelengths (2.3 μm). Methods. We compared two epochs of X-shooter observations, during and after the dimming. We modelled the rarely detected CO bandhead emission in both epochs to examine whether the inner disc properties had changed. The spectral energy distribution was used to derive the extinction properties of the dimmed spectrum and compare the infrared excess between the two epochs. Lines tracing accretion were used to derive the mass accretion rate in both states. Results. The CO originates from a region with physical properties of T = 3000 K, NCO = 1 × 1021 cm−2 and vk sin i = 113 km s−1. The extinction properties of the dimming layer were derived with the effective optical depth ranging from τeff ~2.5−1.5 from the UV to the near-IR. The inferred mass accretion rate Ṁacc is ~1.5 × 10−8 M⊙ yr−1 and ~2 × 10−8 M⊙ yr−1 after and during the dimming respectively. By fitting the spectral energy distribution, additional emission is observed in the infrared during the dimming event from dust grains with temperatures of 500–700 K. Conclusions. The physical conditions traced by the CO are similar for both epochs, indicating that the inner gaseous disc properties do not change during the dimming events. The extinction curve is flatter than that of the interstellar medium, and large grains of a few hundred microns are thus required. When we correct for the observed extinction, the mass accretion rate is constant in the two epochs, suggesting that the accretion is stable and therefore does not cause the dimming. The additional hot emission in the near-IR is located at about 0.5 au from the star and is not consistent with an occulting body located in the outer regions of the disc. The dimming events could be due to a dust-laden wind, a severe puffing-up of the inner rim, or a perturbation caused by the recent star-disc encounter.

scholarly journals Mid-infrared evolution of η Carinae from 1968 to 2018

2019 ◽  
Vol 630 ◽  
pp. L6 ◽  
Author(s):  
A. Mehner ◽  
W.-J. de Wit ◽  
D. Asmus ◽  
P. W. Morris ◽  
C. Agliozzo ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Circumstellar Dust ◽  
Spectral Energy ◽  
Short Term ◽  
Dust Extinction ◽  
Bolometric Luminosity ◽  
Very Large Telescope ◽  
Optical Wavelengths ◽  
The Mean

η Car is one of the most luminous and massive stars in our Galaxy and is the brightest mid-IR source in the sky outside our solar system. Since the late 1990s, the central source has dramatically brightened at UV and optical wavelengths. This might be explained by a decrease in circumstellar dust extinction. We aim to establish the mid-IR flux evolution and further our understanding of the star’s UV and optical brightening. Mid-IR images from 8−20 μm were obtained in 2018 with VISIR at the Very Large Telescope. Archival data from 2003 and 2005 were retrieved from the ESO Science Archive Facility, and historical records were collected from publications. We present mid-IR images of η Car with the highest angular resolution to date at the corresponding wavelengths (≥0.22″). We reconstruct the mid-IR evolution of the spectral energy distribution of the spatially integrated Homunculus nebula from 1968 to 2018 and find no long-term changes. The bolometric luminosity of η Car has been stable over the past five decades. We do not observe a long-term decrease in the mid-IR flux densities that could be associated with the brightening at UV and optical wavelengths, but circumstellar dust must be declining in our line of sight alone. Short-term flux variations within about 25% of the mean levels could be present.

scholarly journals Multiepoch, multiwavelength study of accretion onto T Tauri

2018 ◽  
Vol 618 ◽  
pp. A55 ◽  
Author(s):  
P. C. Schneider ◽  
H. M. Günther ◽  
J. Robrade ◽  
J. H. M. M. Schmitt ◽  
M. Güdel
Keyword(s):  
Near Infrared ◽  
Accretion Rate ◽  
Strong Shock ◽  
Field Configuration ◽  
Optical Data ◽  
X Rays ◽  
Coronal Emission ◽  
X Ray ◽  
T Tauri ◽  
The Impact

Classical T Tauri stars (CTTSs) accrete matter from the inner edge of their surrounding circumstellar disks. The impact of the accretion material on the stellar atmosphere results in a strong shock, which causes emission from the X-ray to the near-infrared (NIR) domain. Shock velocities of several 100 km s−1 imply that the immediate post shock plasma emits mainly in X-rays. Indeed, two X-ray diagnostics, the so-called soft excess and the high densities observed in He-like triplets, differentiate CTTSs from their non-accreting siblings. However, accretion shock properties derived from X-ray diagnostics often contradict established ultraviolet (UV)–NIR accretion tracers and a physical model simultaneously explaining both, X-ray and UV–NIR accretion tracers, is not yet available. We present new XMM-Newton and Chandra grating observations of the CTTS T Tauri combined with UV and optical data. During all epochs, the soft excess is large and the densities derived from the O VII and Ne IX He-like triplets are compatible with coronal densities. This confirms that the soft X-ray emission cannot originate in accretion funnels that carry the bulk of the accretion rate despite T Tauri’s large soft excess. Instead, we propose a model of radially density stratified accretion columns to explain the density diagnostics and the soft excess. In addition, accretion rate and X-ray luminosity are inversely correlated in T Tauri over several epochs. Such an anti-correlation has been observed in samples of stars. Hence the process causing it must be intrinsic to the accretion process, and we speculate that the stellar magnetic field configuration on the visible hemisphere affects both the accretion rate and the coronal emission, eventually causing the observed anti-correlation.

scholarly journals Measuring the physical conditions of accreting gas in T Tauri systems

2007 ◽  
Vol 3 (S243) ◽  
pp. 95-102
Author(s):  
Jeffrey S. Bary ◽  
Sean P. Matt
Keyword(s):  
Near Infrared ◽  
Young Star ◽  
Emission Lines ◽  
Line Flux ◽  
Star Forming ◽  
Physical Conditions ◽  
T Tauri ◽  
Hydrogen Emission Lines ◽  
Line Theory ◽  
Magnetospheric Accretion

AbstractHydrogen emission lines observed from T Tauri stars (TTS) are associated with the accretion/outflow of gas in these young star forming systems. Magnetospheric accretion models have been moderately successful at reproducing the shapes of several Hi emission line profiles, suggesting that the emission arises in the accretion funnels. Despite considerable effort to model and observe these emission features, the physical conditions of the gas confined to the funnel flows remain poorly constrained by observation. We conducted a mutli-epoch near-infrared spectroscopic survey of 16 actively accreting classical TTS in the Taurus-Auriga star forming region. We present an analysis of these simultaneously acquired line flux ratios of many Paschen and Brackett series emission lines, in which we compare the observed ratios to those predicted by the Case B approximation of hydrogen recombination line theory. We find that the line flux ratios for the Paschen and Brackett decrements as well as a comparison between Brγ and Paschen transitions agree well with the Case B models with T < 5000 K and ne ≈ 1010 cm−3.

scholarly journals V899 Mon: A Peculiar Eruptive Young Star Close to the End of Its Outburst

2021 ◽  
Vol 923 (2) ◽  
pp. 171
Author(s):  
Sunkyung Park ◽  
Ágnes Kóspál ◽  
Fernando Cruz-Sáenz de Miera ◽  
Michał Siwak ◽  
Marek Dróżdż ◽  
...  
Keyword(s):  
Loss Rate ◽  
Near Infrared ◽  
Accretion Rate ◽  
Mass Loss Rate ◽  
Young Star ◽  
Light Curves ◽  
Emission Lines ◽  
Spectroscopic Observations ◽  
Photometric Monitoring ◽  
Physical Changes

Abstract The eruptive young star V899 Mon shows characteristics of both FUors and EXors. It reached a peak brightness in 2010, then briefly faded in 2011, followed by a second outburst. We conducted multifilter optical photometric monitoring, as well as optical and near-infrared spectroscopic observations, of V899 Mon. The light curves and color–magnitude diagrams show that V899 Mon has been gradually fading after its second outburst peak in 2018, but smaller accretion bursts are still happening. Our spectroscopic observations taken with Gemini/IGRINS and VLT/MUSE show a number of emission lines, unlike during the outbursting stage. We used the emission line fluxes to estimate the accretion rate and found that it has significantly decreased compared to the outbursting stage. The mass-loss rate is also weakening. Our 2D spectroastrometric analysis of emission lines recovered jet and disk emission of V899 Mon. We found that the emission from permitted metallic lines and the CO bandheads can be modeled well with a disk in Keplerian rotation, which also gives a tight constraint for the dynamical stellar mass of 2 M ⊙. After a discussion of the physical changes that led to the changes in the observed properties of V899 Mon, we suggest that this object is finishing its second outburst.

scholarly journals The 2016–2017 peak luminosity of the pre-main sequence variable V2492 Cygni

2018 ◽  
Vol 611 ◽  
pp. A54 ◽  
Author(s):  
T. Giannini ◽  
U. Munari ◽  
S. Antoniucci ◽  
D. Lorenzetti ◽  
A. A. Arkharov ◽  
...  
Keyword(s):  
High Resolution ◽  
Main Sequence ◽  
Near Infrared ◽  
Accretion Rate ◽  
High State ◽  
Physical Origin ◽  
Mass Accretion Rate ◽  
Gas Kinematics ◽  
Peak Luminosity ◽  
Present Event

Context. V2492 Cyg is a young pre-main sequence star presenting repetitive brightness variations of significant amplitude (ΔR ≥ 5 mag) whose physical origin has been ascribed to both extinction (UXor-type) and accretion (EXor-type) variability, although their mutual proportion has not been clarified yet. Recently, V2492 Cyg has reached a level of brightness ever registered in the period of its documented activity.Aim. We aim to derive the variation of the mass accretion rate between low- and high-state and to get new insights on the origin of the variability of V2492 Cyg.Methods. Optical and near-infrared (NIR) photometry and spectroscopy have been obtained in October 2016 and between March and July 2017. The source has remained bright until the end of May 2017, then it started to rapidly fade since the beginning of June at a rate of ~0.08 mag/day. On mid-July 2017 the source has reached the same low-brightness level as two years before. Extinction and mass accretion rate were derived by means of the luminosity of the brightest lines, in particular Hα and Hβ. A couple of optical high-resolution spectra are also presented to derive information on the gas kinematics.Results. Visual extinction variations do not exceed a few magnitudes, while the mass accretion rate is estimated to vary from less than 10−8 up to a few 10−7 M⊙ yr−1. This latter is comparable to that estimated on the previous high-state in 2010, likely occurred under more severe extinction conditions.Conclusions. The combined analysis of the optical and NIR observations extends to the present event the original suggestion that the V2492 Cyg variability is a combination of changing extinction and accretion.

scholarly journals A Comparative Anatomy of Dusty Disks Imaged by NICMOS

2004 ◽  
Vol 202 ◽  
pp. 308-315
Author(s):  
Glenn Schneider ◽  
Dean C. Hines ◽  
Murray Silverstone ◽  
Alycia J. Weinberger ◽  
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Hubble Space Telescope ◽  
Comparative Anatomy ◽  
Scattered Light ◽  
Infrared Camera ◽  
Main Sequence Stars ◽  
Spatially Resolved ◽  
T Tauri ◽  
Dusty Disks

Using the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope we have conducted a coronagraphic imaging survey of 18 main sequence stars with large infrared excesses, searching for circumstellar dust (debris) in scattered light. Dusty disks with radial and hemispheric brightness anisotropies and complex morphologies, both possibly indicative of dynamical interactions with unseen planetary mass companions, were spatially resolved and imaged around three young (≲ 10Myr old) stars. From these observations we describe the debris systems around: a) HR 4796A (A0V), a 70 AU radius ring less than 14 AU wide with unequal ansal flux densities; b) HD 141569A (Herbig Ae/Be), a 400 AU radius disk with a 40 AU wide gap; and c) TW Hya (K7 T-Tauri), a pole-on circularly symmetric disk with a radial break in its surface density of scattering particles. Additionally, our non-detection of scattered light and high precision photometry of a fourth system of similar age, HD 98800 A/B, coupled with mid and thermal IR measurements, greatly constrain a likely model for the debris about the B component.

scholarly journals Statistical studies of flare stars and other flashing objects carried out at the Byurakan Observatory

2021 ◽  
pp. 150-162
Author(s):  
A. A. Akopian
Keyword(s):  
Open Clusters ◽  
Physical Parameters ◽  
Evolutionary Status ◽  
Flare Activity ◽  
Short Term ◽  
T Tauri ◽  
Statistical Studies ◽  
Flare Stars

The review briefly presents the statistical studies of flare stars and related objects carried out at the Byurakan Astrophysical Observatory, in particular: i) determination of the evolutionary status of flare stars, ii) an explanation of the observed difference between flare stars of the galactic field (type UV Cet) and flare stars of systems (open clusters, associations), iii) the connection between flare stars and T Tauri stars, iv) short-term and long-term (evolutionary) variability of flare activity, v) original statistical methods developed for the study of flare stars and their systems, vi) recent advances in research on flashing objects. This review does not present such important areas of research on flare stars as the determination of physical parameters, photometry and colorimetry of stars and their flares, detailed studies of individual stars, theoretical works on possible mechanisms of flares. These areas were well presented in many books and reviews by Ambartsumian and Mirzoyan.

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