Variabiity of young stellar objects: Accretion, disks, outflows, and magnetic activity

Stelzer, B.

doi:10.1002/asna.201512185

Cited by 3 publications

(4 citation statements)

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“…Variability in Herbig Ae/Be stars predominantly occurs due to the obscuration Article number, page 1 of 17 arXiv:1906.00256v1 [astro-ph.SR] 1 Jun 2019 A&A proofs: manuscript no. IC5070 from the circumstellar dust (Bertout 1989;Herbst et al 1994Herbst et al , 2007Semkov 2011;Stelzer 2015). Since, YSOs exhibit different variability signatures, exploring their variable properties at multiple wavelengths is essential to understand the complex nature of these stars in both short and long time-scales.…”

Section: Introductionmentioning

confidence: 99%

“…In CTTSs, variability is caused by the variable accretion from the circumstellar disk onto the star, where both the accretion rate and the distribution of accretion zone or hot-spots over the stellar surface are not uniform (Herbst et al 2007;Cody et al 2014). Variability in Herbig Ae/Be stars predominantly occurs due to the obscuration from the circumstellar dust (Bertout 1989;Herbst et al 1994Herbst et al , 2007Semkov 2011;Stelzer 2015). Since, YSOs exhibit different variability signatures, exploring their variable properties at multiple wavelengths is essential to understand the complex nature of these stars in both short and long time-scales.…”

Section: Introductionmentioning

confidence: 99%

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

Bhardwaj

Panwar

Herczeg

et al. 2019

A&A

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Context. Pre-main-sequence variability characteristics are useful to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. 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 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. Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalogue 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 up to a couple of 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% variables exhibit strong periodic signatures attributed to cold spot modulations. In case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable over the year-long time-scale.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Bhardwaj

Panwar

Herczeg

et al. 2019

A&A

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“…Variability can occur both on long (>> years) and short (hours -days) time scales. Longer term, gradual variability is attributed to the global evolution of the stellar magnetic field topology and/or disk accretion properties (e.g., Feigelson & Montmerle 1999;Stelzer 2015). Shorter term variability is associated with magnetic reconnection events in the corona, similar to solar X-ray flares but with greater magnitude and frequency (e.g., Feigelson et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Variable H¹³CO⁺ Emission in the IM Lup Disk: X-Ray Driven Time-dependent Chemistry?

Cleeves

Bergin

Öberg

et al. 2017

ApJL

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We report the first detection of a substantial brightening event in an isotopologue of a key molecular ion, HCO + , within a protoplanetary disk of a T Tauri star. The H 13 CO + J = 3−2 rotational transition was observed three times toward IM Lup between July 2014 and May 2015 with the Atacama Large Millimeter Array. The first two observations show similar spectrally integrated line and continuum fluxes, while the third observation shows a doubling in the disk integrated J = 3−2 line flux compared to the continuum, which does not change between the three epochs. We explore models of an X-ray active star irradiating the disk via stellar flares, and find that the optically thin H 13 CO + emission variation can potentially be explained via X-ray driven chemistry temporarily enhancing the HCO + abundance in the upper layers of the disk atmosphere during large or prolonged flaring events. If the HCO + enhancement is indeed caused by a X-ray flare, future observations should be able to spatially resolve these events and potentially enable us to watch the chemical aftermath of the high-energy stellar radiation propagating across the face of protoplanetary disks, providing a new pathway to explore ionization physics and chemistry, including electron density, in disks.

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“…We showed that a continuously driven stellar jet forms a stationary X-ray emitting shock at the base with physical parameters in good agreement with observations. According to the YSO jets phenomenology described in this section, we do not expect a continuous flow propagating but rather a variable perturbed plasma (see Stelzer 2015Stelzer , 2017 for a brief description of the variability observed at YSOs). Here we aim at investigating the effect of perturbations in the X-ray emitting stationary shocks formed at the base of stellar jets described in Ustamujic et al (2016).…”

Section: Introductionmentioning

confidence: 99%

Structure of X-ray emitting jets close to the launching site: from embedded to disk-bearing sources

Ustamujic

Orlando

Bonito

et al. 2018

A&A

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Context. Several observations of stellar jets show evidence of X-ray emitting shocks close to the launching site. In some cases, the shocked features appear to be stationary, also for Young Stellar Objects (YSOs) at different stages of evolution. We study the case of HH 154, the jet originating from the embedded binary Class 0/I protostar IRS 5, and the case of the jet associated to DG Tau, a more evolved Class II disk-bearing source or Classical T Tauri star (CTTS), both located in the Taurus star-forming region. Aims. We aim at investigating the effect of perturbations in X-ray emitting stationary shocks in stellar jets; the stability and detectability in X-rays of these shocks; and explore the differences in jets from Class 0 to Class II sources. Methods. We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations that modelled supersonic jets ramming into a magnetized medium. The jet is formed by two components: a continously driven component that forms a quasi-stationary shock at the base of the jet; and a pulsed component constituted by blobs perturbing the shock. We explored different parameters for both components. We studied two cases: a jet less dense than the ambient medium (light jet), representing the case of HH 154; and a jet denser than the ambient (heavy jet), associated with DG Tau. We synthesized the count rate from the simulations and compared with available Chandra observations. Results. Our model explains the formation of X-ray emitting quasi-stationary shocks observed at the base of jets in a natural way, being able to reproduce the observed jet properties at different evolutionary phases (in particular, for HH 154 and DG Tau). The jet is collimated by the magnetic field forming a quasi-stationary shock at the base which emits in X-rays even when perturbations formed by a train of blobs are present. We found similar collimation mechanisms dominating in both heavy and light jets. Conclusions. We derived the pysical parameters that can give rise to X-ray emission consistent with observations of HH 154 and DG Tau. We have also performed a wide exploration of the parameter space characterizing the model; this can represent a useful tool to study and diagnose the physical properties of YSO jets over a broad range of physical conditions, from embedded to disk-bearing sources. We have shown that luminosity did not change significantly in variable jet models for the range of parameters explored. Finally, we provided an estimation of the maximum perturbations that can be present in HH 154 and DG Tau taking into account the available X-ray observations.

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Variabiity of young stellar objects: Accretion, disks, outflows, and magnetic activity

Abstract: Variability is a key characteristic of young stars. Two major origins may be distinguished: a scaled-up version of the magnetic activity seen on main-sequence stars and various processes related to circumstellar disks, accretion, and outflows.

Cited by 3 publications

References 75 publications

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

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

Variable H¹³CO⁺ Emission in the IM Lup Disk: X-Ray Driven Time-dependent Chemistry?

Structure of X-ray emitting jets close to the launching site: from embedded to disk-bearing sources

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Variabiity of young stellar objects: Accretion, disks, outflows, and magnetic activity

Abstract: Variability is a key characteristic of young stars. Two major origins may be distinguished: a scaled-up version of the magnetic activity seen on main-sequence stars and various processes related to circumstellar disks, accretion, and outflows.

Cited by 3 publications

References 75 publications

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

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

Variable H13CO+ Emission in the IM Lup Disk: X-Ray Driven Time-dependent Chemistry?

Structure of X-ray emitting jets close to the launching site: from embedded to disk-bearing sources

Contact Info

Product

Resources

About

Variable H¹³CO⁺ Emission in the IM Lup Disk: X-Ray Driven Time-dependent Chemistry?