A Continuum of Accretion Burst Behavior in Young Stars Observed by K2

Cody, Ann Marie; Hillenbrand, Lynne A.; David, Trevor J.; Carpenter, John M.; Everett, Mark E.; Howell, Steve B.

doi:10.3847/1538-4357/836/1/41

Cited by 68 publications

(86 citation statements)

References 155 publications

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“…During the K2 portion of the mission, because only two reaction wheels can be used, the whole spacecraft slowly drifts and then repositions regularly every 0.245 days. This drift is ∼0 1 per hour (Cody et al 2017).…”

Section: K2 Datamentioning

confidence: 99%

Rotation of Late-type Stars in Praesepe with K2

Rebull

Stauffer

Hillenbrand

et al. 2017

ApJ

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104

133

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We have Fourier-analyzed 941 K2 light curves (LCs) of likely members of Praesepe, measuring periods for 86% and increasing the number of rotation periods (P) by nearly a factor of four. The distribution of P versus -( ) V K s , a mass proxy, has three different regimes:, where the rotation rate rapidly slows as mass decreases; 1.3< -( ) V K s <4.5, where the rotation rate slows more gradually as mass decreases; andwhere the rotation rate rapidly increases as mass decreases. In this last regime, there is a bimodal distribution of periods, with few between ∼2 and ∼10 days. We interpret this to mean that once M stars start to slow down, they do so rapidly. The K2 period-color distribution in Praesepe (∼790 Myr) is much different than that in the Pleiades (∼125 Myr) for late F, G, K, and early-M stars; the overall distribution moves to longer periods and is better described by two line segments. For mid-M stars, the relationship has a similarly broad scatter and is steeper in Praesepe. The diversity of LCs and of periodogram types is similar in the two clusters; about a quarter of the periodic stars in both clusters have multiple significant periods. Multi-periodic stars dominate among the higher masses, starting at a bluer color in Praesepe ( -( ) V K s ∼1.5) than in the Pleiades ( -( ) V K s ∼2.6). In Praesepe, there are relatively more LCs that have two widely separated periods, D > P 6 days. Some of these could be examples of M star binaries where one star has spun down but the other has not.

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Section: K2 Datamentioning

confidence: 99%

Rotation of Late-type Stars in Praesepe with K2

Rebull

Stauffer

Hillenbrand

et al. 2017

ApJ

Self Cite

104

133

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“…Accretion variability is common in young stellar objects, as 10% of CTTSs have similar bursty light curves (Findeisen et al 2013;Cody et al 2014Cody et al , 2017Stauffer et al 2014). The variable accretion process appears as changes in excess continuum and line emission above the photosphere (e.g., Alencar et al 2012;Fang et al 2013;Costigan et al 2014), and the corresponding changes in photometry (Venuti et al 2014;Sousa et al 2016;Stauffer et al 2016;Tofflemire et al 2017a) are driven by either unsteady star-disk connections (e.g., Romanova et al 2013) or changes in the disk density at the inner rim (Robinson et al 2017).…”

Section: Introductionmentioning

confidence: 99%

“…The photometric variability of T Tauri stars has been studied for decades (Wenzel 1969;Grinin 1988;Herbst et al 1994;Bouvier et al 2013;Cody et al 2017). When star-disk interactions are steady, an accretion column and the associated inner disk warp rotate around the star, periodically occulting the central star (e.g., Bouvier et al 2007;McGinnis et al 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Spot modulation is also commonly seen among young stars with typical variations of  DV 0.5 mag (e.g., Herbst et al 1994;Grankin et al 2007), although spots in light curves of some CTTSs can be difficult to distinguish from extinction and accretion variations. Extinction, accretion, and spot variability each have particular patterns in high time-resolution photometry (Alencar et al 2010(Alencar et al , 2012Morales-Calderón et al 2011;Cody et al 2017), multiband photometry (Herbst et al 1994;Grankin et al 2007;Venuti et al 2015), and spectroscopic monitoring .…”

Section: Introductionmentioning

confidence: 99%

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Star–Disk Interactions in Multiband Photometric Monitoring of the Classical T Tauri Star GI Tau

Guo

Herczeg

Jose

et al. 2018

ApJ

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The variability of young stellar objects is mostly driven by star-disk interactions. In long-term photometric monitoring of the accreting T Tauri star GI Tau, we detect extinction events with typical depths of DṼ 2.5 mag that last for days to months and often appear to occur stochastically. In 2014-2015, extinctions that repeated with a quasi-period of 21 days over several months are the first empirical evidence of slow warps predicted by magnetohydrodynamic simulations to form at a few stellar radii away from the central star. The reddening is consistent with =  R 3.85 0.5 V and, along with an absence of diffuse interstellar bands, indicates that some dust processing has occurred in the disk. The 2015-2016 multiband light curve includes variations in spot coverage, extinction, and accretion, each of which results in different traces in color-magnitude diagrams. This light curve is initially dominated by a month-long extinction event and a return to the unocculted brightness. The subsequent light curve then features spot modulation with a 7.03 day period, punctuated by brief, randomly spaced extinction events. The accretion rate measured from U-band photometry ranges from´-1.3 10 8 to´-1.1 10 10 M e yr −1 (excluding the highest and lowest 5% of high-and low-accretion rate outliers), with an average of4.7 -10 9 M e yr −1 . A total of 50% of the mass is accreted during bursts of >´-12.8 10 9 M e yr -1, which indicates limitations on analyses of disk evolution using single-epoch accretion rates.

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“…Those light curves provide a hunting ground for the search for newly formed planets via their transits (David et al 2016b;Mann et al 2016), for the identification of YSO eclipsing binaries Kraus et al 2015;Lodieu et al 2015;David et al 2016a), and for the determination of the rotational periods for a large sample of low-mass stars of 5-10 Myr age (L. Rebull et al 2017, in preparation). A small fraction of the Upper Sco YSOs have IR excesses and are likely classical TTauri stars (CTTs); a subgroup of "burster" light curves associated with some of these accreting systems is discussed in Cody et al (2017).…”

Section: Introductionmentioning

confidence: 99%

Orbiting Clouds of Material at the Keplerian Co-rotation Radius of Rapidly Rotating Low-mass WTTs in Upper Sco

Stauffer

Cameron

Jardine

et al. 2017

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137

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Using K2 data, we identified 23 very-low-mass members of the ρ Oph and Upper Scorpius star-forming region as having periodic photometric variability not easily explained by well-established physical mechanisms such as star spots, eclipsing binaries, or pulsation. All of these unusual stars are mid-to-late M dwarfs without evidence of active accretion, and with photometric periods generally <1 day. Often the unusual light-curve signature takes the form of narrow flux dips; when we also have rotation periods from star spots, the two periods agree, suggesting that the flux dips are due to material orbiting the star at the Keplerian co-rotation radius. We sometimes see "statechanges" in the phased light-curve morphologies where ∼25% of the waveform changes shape on timescales less than a day; often, the "state-change" takes place immediately after a strong flare. For the group of stars with these sudden light-curve morphology shifts, we attribute their flux dips as most probably arising from eclipses of warm coronal gas clouds, analagous to the slingshot prominences postulated to explain transient Hα absorption features in AB Doradus and other rapidly rotating late-type stars. For another group of stars with somewhat longer periods, we find the short-duration flux dips to be highly variable on both short and long timescales, with generally asymmetric flux-dip profiles. We believe that these flux dips are due to particulate clouds possibly associated with a close-in planet or resulting from a recent collisional event.

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A Continuum of Accretion Burst Behavior in Young Stars Observed by K2

Cited by 68 publications

References 155 publications

Rotation of Late-type Stars in Praesepe with K2

Rotation of Late-type Stars in Praesepe with K2

Star–Disk Interactions in Multiband Photometric Monitoring of the Classical T Tauri Star GI Tau

Orbiting Clouds of Material at the Keplerian Co-rotation Radius of Rapidly Rotating Low-mass WTTs in Upper Sco

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