Variability in ultra cool dwarfs: Evidence for the evolution of surface features

By C. Mundt. 2000

156 citations recorded by the source corpus.

We present photometric light curves for a sample of 21 ultra cool M and L dwarfs in the field and in the young open clusters σ Orionis and the Pleiades. The list of targets includes both low mass hydrogen burning stars and brown dwarfs. Evidence for variability with rms amplitudes (in the I band) of 0.01 to 0.055 magnitudes on timescales of 0.4 to 100 hours is discovered in half of these objects. Power spectral analysis using the CLEAN algorithm was performed to search for evidence of periodic variability. Some objects show strong periodicities at around a few hours, which could be due to rotational modulation of the light curve by surface features. However, several objects do not have any significant periodicities to explain their variability. The $v \sin i$ values of a similar population of objects makes it very likely that our time sampling was sensitive to the expected range of rotation periods, and simulations show that we would have detected these if they were caused by long-lived surface features. We argue that this absence of periodicity is due to the evolution of the brightness, and presumably also the physical size, of surface features on timescales of a few to a few tens of hours. This is supported in the case of 2M1145 for which two light curves have been obtained one year apart and show no common periodicity. The surface features could plausibly be photospheric dust clouds or magnetically-induced spots. The recently observed decline in chromospheric activity for late type M and L dwarfs hints towards the former explanation for at least our later-type objects. Furthermore, our sample suggests that variability is more common in objects later than M9, indicating that the variability may be related to dust formation. One light curve shows a brief, but significant, dip, which could be a short-lived feature or possibly an eclipse by a companion.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/5d63a2d8bfdd6bebea321e5ab2f8e0316e32b97c

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Citations in the corpus

Infrared Photometry of Late-M, L, and T Dwarfs (2001, background): “Bailer-Jones & Mundt (2001) have reported variability at the 5% level in the I-band for M and L dwarfs, which they suggest is due to dust formation.”
LARGE-AMPLITUDE VARIATIONS OF AN L/T TRANSITION BROWN DWARF: MULTI-WAVELENGTH OBSERVATIONS OF PATCHY, HIGH-CONTRAST CLOUD FEATURES (2012, background): “Observations in the red optical (Bailer-Jones & Mundt 2001; Gelino et al. 2002; Koen 2003, 2004, 2005a,b) have targeted mainly late-M and early-L dwarfs due to a drop-off in optical flux for later spectral types.”
Brown Dwarf Companions to G-Type Stars. I. Gliese 417B and Gliese 584C (2001, background): “Bailer-Jones & Mundt (2001) find that photometric variability is more common in L dwarfs than in late-M dwarfs; since chromospheric activity is seen to drop from late-M to early-L (Gizis et al. 2000a), these authors suggest that starspots are unlikely to be the correct explanation.”
On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, background): “…revealed periodic and non-periodic flux variations as large as 10–30% (Radigan et al. 2012; Gillon et al. 2013), occurring on timescales from 1–100 hr (Bailer-Jones & Mundt 2001), and spectroscopic observations have shown that variability can be strongly wavelength-dependent (Buenzli et al. 2012).”
Evidence of Cloud Disruption in the L/T Dwarf Transition (2002, background): “Such weather phenomena have been previously cited to explain nonperiodic variability in late-type M and early-type L dwarfs (Bailer-Jones & Mundt 2001; Martı´n, Zapatero Osorio, & Lehto 2001).”
WEATHER ON OTHER WORLDS. II. SURVEY RESULTS: SPOTS ARE UBIQUITOUS ON L AND T DWARFS (2014, background): “For example, Bailer-Jones & Mundt (2001) note that despite a peak in the periodogram of the L5 dwarf SDSSp J053951.”
Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs (2002, background): “Another problem related to dust is if it may induce some meteorological phenomena which may explain the unknown type of observed light variations in some ultracool dwarfs (e.g. Bailer-Jones & Mundt 2001; Mart́in, Zapatero Osorio, & Lehto 2001).”
PHOTOMETRIC VARIABILITY OF THE T2.5 BROWN DWARF SIMP J013656.5+093347: EVIDENCE FOR EVOLVING WEATHER PATTERNS (2009, background): “…in theI band and clearly established that roughly half of these objects display variability on timescales ranging from tens of minutes to weeks, with amplitudes of a few tens of mmag (Tinney & Tolley 1999; Gelino et al. 2002; Bailer-Jones & Mundt 2001; Terndrup et al. 1999; Martín et al. 2001).”
The Spectra of T Dwarfs. I. Near-Infrared Data and Spectral Classification (2001, background): “…Figure 18 may be intrinsic to the source, as a number of L- and T-type brown dwarfs have recently been shown to be variable, both photometrically (Bailer-Jones & Mundt 1999, 2001) and spectroscopically (Nakajima et al. 2000; Kirkpatrick et al. 2001a), likely due to patchy clouds of dust in the…”
Precipitating Condensation Clouds in Substellar Atmospheres (2001, background): “Nonuniform Clouds Variable brightness in the I band has been detected for some L dwarfs by Bailer-Jones & Mundt (2001), who attribute the variability to evolution of dust clouds.”
A Unified Near-Infrared Spectral Classification Scheme for T Dwarfs (2005, background): “While a number of studies have measured photometric variability of up to 0.5 mag in several L and T dwarfs (Bailer-Jones & Mundt 1999, 2001; Tinney & Tolley 1999; Gelino et al. 2002; Enoch, Brown & Burgasser 2003; Bailer-Jones & Lamm 2003; Koen 2003, 2004), only one T dwarf has been monitored for…”