The frequency of large variations in the near-infrared fluxes of T Tauri stars

Scholz, Alexander

doi:10.1111/j.1365-2966.2011.20136.x

Cited by 37 publications

(44 citation statements)

References 42 publications

(61 reference statements)

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“…This view is supported by new survey results (e.g. [20,21]) that report frequent large luminosity variations in young forming stars.…”

Section: Ex Lupi and Other Exors: Extreme Versions Of A Larger Class?supporting

confidence: 53%

Dead discs, unstable discs and the stars they surround

D’Angelo

2014

EPJ Web of Conferences

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Abstract. Strong stellar magnetic fields significantly alter the behaviour of surrounding accretion discs. Recent work has demonstrated that at low accretion rates a large amount of mass can remain confined in the disc, contrary to the standard assumption that the magnetic field will expel the disc in an outflow (the "propeller regime"). These "dead discs" often become unstable, causing cycles of accretion onto the central star. Here I present the main predictions of this model, and argue that it provides a good explanation for the peculiar behaviour seen in several accreting sources with strong magnetic fields. I will focus in particular on three accreting millisecond X-ray pulsars: SAX J1808.4-3658, NGC 6440 X-2 and IGR J00291+5934. These sources all show low-frequency quasiperiodic oscillations consistent with a variable accretion rate, as well as unusual outburst patterns that suggest gas is confined in the inner disc regions during quiescence.

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“…This view is supported by new survey results (e.g. [20,21]) that report frequent large luminosity variations in young forming stars.…”

Section: Ex Lupi and Other Exors: Extreme Versions Of A Larger Class?supporting

confidence: 53%

Dead discs, unstable discs and the stars they surround

D’Angelo

2014

EPJ Web of Conferences

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“…This object has been studied by Wilking et al (2005) who reported a SpT of M3.5 with no particular comments, only that there were strong emission lines in the spectrum. Scholz (2012) has also noted that this object is extremely variable in the near infrared, with variations up to ∼0.9 mag in K-band. The flux calibration of the spectrum analyzed here is compatible with the 2MASS photometry in J-and H-bands, and it was only correct by a factor 1.12 to account for slit losses to match these bands.…”

Section: A3 Iso−oph123mentioning

confidence: 85%

“…The total population of the surrounding Ophiucus region is estimated to be of around 300 YSOs , with ∼200 YSOs located in ρ-Oph itself. Given the large quantity of YSOs present in this cluster and its proximity, it has been extensively studied in the past at various wavelengths from optical, near-and far-infrared, millimeter, radio, to X-ray (e.g., Greene & Meyer 1995;Luhman & Rieke 1999;Wilking et al 2005;Alves de Oliveira et al 2010, 2012Bontemps et al 2001;McClure et al 2010;Gagné et al 2004).…”

Section: Introductionmentioning

confidence: 99%

X-Shooter study of accretion inρ-Ophiucus: very low-mass stars and brown dwarfs

Manara

Testi

Natta

et al. 2015

A&A

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We present new VLT/X-Shooter optical and near-infrared spectra of a sample of 17 candidate young low-mass stars and brown dwarfs located in the ρ-Ophiucus cluster. We derived the spectral type and extinction for all the targets, and then we determined their physical parameters. All the objects but one have M 0.6 M , and eight have mass below or close to the hydrogen-burning limit. Using the intensity of various permitted emission lines present in their spectra, we determined the accretion luminosity and mass accretion rates (Ṁ acc ) for all the objects. When compared with previous works targeting the same sample, we find that, in general, these objects are not as strongly accreting as previously reported, and we suggest that the reason is our more accurate estimate of the photospheric parameters. We also compare our findings with recent works in other slightly older star-forming regions, such as Lupus, to investigate possible differences in the accretion properties, but we find that the accretion properties for our targets have the same dependence on the stellar and substellar parameters as in the other regions. This leads us to conclude that we do not find evidence for a different dependence ofṀ acc with M when comparing low-mass stars and brown dwarfs. Moreover, we find a similar small ( 1 dex) scatter in theṀ acc −M relation as in some of our recent works in other star-forming regions, and no significant differences inṀ acc due to different ages or properties of the regions. The latter result suffers, however, from low statistics and sample selection biases in the current studies. The small scatter in theṀ acc −M correlation confirms that mass accretion rate measurements in the literature based on uncertain photospheric parameters and single accretion indicators, such as the Hα width, can lead to a scatter that is unphysically large. Our studies show that only broadband spectroscopic surveys coupled with a detailed analysis of the photospheric and accretion properties allows us to properly study the evolution of disk accretion rates in star-forming regions.Key words. stars: pre-main sequence -stars: formation -brown dwarfs -protoplanetary disks -accretion, accretion disksopen clusters and associations: individual: rho-Ophiucus IntroductionThe evolution of protoplanetary disks surrounding forming stars has been a major subject of study in recent years. The interest in this topic is driven by the fact that disks are the birthplace of planets. A clear understanding of the physical mechanisms driving the formation, evolution, and dispersal of disks is thus needed to constrain planet formation theories, and to explain the observed properties of our own solar system and of the wealth of exoplanetary systems discovered so far.During their evolution, the central young stellar object (YSO) and the surrounding disk interact through multiple processes, such as photoevaporation, stellar winds, and accretion of matter. The latter is a result of viscous processes happening in the disk, which drive its secular evolu...

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“…More recently, Rice et al (2012) have monitored the dark cloud L 1003 in Cygnus OB7 at NIR wavelengths with UKIRT over a time span of 1.5 years, and Morales et al (2011Morales et al ( , 2012 collected multi-epoch, multi-color light curves of candidate members of the Orion nebular cluster region during their dedicated Warm Spitzer Exploration Science Program YSOVAR (complemented by UKIRT and CFHT data). Likewise, a comprehensive longterm (meanwhile spanning 8 yrs) monitoring campaign of NIR variability in a large sample of brown dwarfs and T Tauri stars has been carried out by Scholz and collaborators (Scholz et al 2009;Scholz 2012).…”

Section: Introductionmentioning

confidence: 99%

Near-infrared variability in the star-forming region RCW 38

Dörr

Chini

Haas

et al. 2013

A&A

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Aims. We want to study the content of young stellar objects in the RCW 38 cluster by means of multi-epoch variability studies. Methods. We performed a three-month near-infrared (NIR) monitoring campaign of the young cluster RCW 38 using the 80 cm IRIS telescope near Cerro Armazones, Chile. Variability data with a median sampling of 1 day was gathered for 1026 sources, while a total of 3433 sources in JHK could be studied in the co-added, deep images with a completeness limit of K < 15 mag. Results. We find that 139 sources were identified as variable with amplitudes above 10% in H and K, and 47% of these variables have been classified as candidate young stars by previous X-ray and mid-infrared studies. Although the majority of the variable sources show no K-excess, their high extinction and concentration towards the cluster center, together with their irregular variability behavior, suggest that they are also candidate young stellar objects. Most of them are likely low-mass sources with variability amplitudes typical of T Tauri stars. The majority of previously suggested OB candidates appear to be intermediate-mass pre-main sequence sources on the basis of their JHK properties. Conclusions. NIR variability is an efficient tool for detecting new, embedded, young stellar objects that have escaped previous X-ray and mid-infrared studies.

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The frequency of large variations in the near-infrared fluxes of T Tauri stars

Cited by 37 publications

References 42 publications

Dead discs, unstable discs and the stars they surround

Dead discs, unstable discs and the stars they surround

X-Shooter study of accretion inρ-Ophiucus: very low-mass stars and brown dwarfs

Near-infrared variability in the star-forming region RCW 38

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