Spot modelling of the flare M4.5 dwarf YZ CMi

Zboril, M.

doi:10.1002/asna.200310162

Cited by 15 publications

(17 citation statements)

References 11 publications

(9 reference statements)

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“…This small difference will arise due to the differing ratio of the Planck function of the spot and the star due to their different temperatures; however, this difference will be muted as we move into the near infrared. For instance, assuming that GJ 1214 has spots 500 K cooler -a value supposedly consistent with another M4.5 dwarf (Zboril et al 2003) -than GJ 1214's ∼3000 K effective temperature (Charbonneau et al 2009), the 2.0% variability due to rotational modulation in the MEarth bandpass (∼780 nm), will translate into 1.5%, and 1.0% variability in J-band and Ks-band, respectively. Assuming the unspotted transit depth is 1.350% in these bands then the maximum transit depths from unocculted spots, which would results from measurements at the minimum flux of the observed rotational modulation, would be 1.369% in J and 1.364% in Ks-band.…”

Section: Gj 1214b's Transit Depth In the Near-infraredmentioning

confidence: 97%

BROADBAND TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH GJ 1214b SUGGESTS A LOW MEAN MOLECULAR WEIGHT ATMOSPHERE

Croll

Jayawardhana

et al. 2011

ApJ

140

190

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We used the Wide-field Infrared Camera on the Canada-France-Hawaii telescope to observe four transits of the super-Earth planet GJ 1214b in the near-infrared. For each transit we observed in two bands nearly-simultaneously by rapidly switching the WIRCam filter wheel back and forth for the duration of the observations. By combining all our J-band (∼1.25 µm) observations we find a transit depth, analogous to the planet-to-star radius ratio squared, in this band of (R P J /R * ) 2 =1.338±0.013% -a value consistent with the optical transit depth reported by Charbonneau and collaborators. However, our best-fit combined Ks-band (∼2.15 µm) transit depth is deeper: (R P Ks /R * ) 2 =1.438±0.019%. Formally our Ks-band transits are deeper than the J-band transits observed simultaneously by a factor of (R P Ks /R P J ) 2 =1.072±0.018 -a 4σ discrepancy. The most straightforward explanation for our deeper Ks-band transit depth is a spectral absorption feature from the limb of the atmosphere of the planet; for the spectral absorption feature to be this prominent the atmosphere of GJ 1214b must have a large scale height and a low mean molecular weight. That is, its atmosphere would have to be hydrogen/helium dominated and this planet would be better described as a mini-Neptune. However, recently published observations from 0.78 -1.0 µm, by Bean and collaborators, show a lack of spectral features and transit depths consistent with those obtained by Charbonneau and collaborators. The most likely atmospheric composition for GJ 1214b that arises from combining all these observations is less clear; if the atmosphere of GJ 1214b is hydrogen/helium dominated then it must have either a haze layer that is obscuring transit depth differences at shorter wavelengths, or significantly different spectral features than current models predict. Our observations disfavour a water-world composition, but such a composition will remain a possibility for GJ 1214b, until observations reconfirm our deeper Ks-band transit depth or detect features at other wavelengths.

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Section: Gj 1214b's Transit Depth In the Near-infraredmentioning

confidence: 97%

BROADBAND TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH GJ 1214b SUGGESTS A LOW MEAN MOLECULAR WEIGHT ATMOSPHERE

Croll

Jayawardhana

et al. 2011

ApJ

140

190

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“…Bondar' et al (2019) found an activity cycle of 27.5 ± 2.0 yr, estimated from more than 80 years of archival photometric observations, with peak-to-peak variations of 0.2−0.3 mag. Estimations of the effective temperature of YZ CMi range from 3045 K (from synthetic spectra fitting; Rojas-Ayala et al 2012) to 3600 K (from spectral color indices; Zboril 2003).…”

Section: The Active Star Yz CMImentioning

confidence: 99%

The CARMENES search for exoplanets around M dwarfs

Baroch

Morales

Ribas

et al. 2020

A&A

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Context. Variability caused by stellar activity represents a challenge to the discovery and characterization of terrestrial exoplanets and complicates the interpretation of atmospheric planetary signals. Aims. We aim to use a detailed modeling tool to reproduce the effect of active regions on radial velocity measurements, which aids the identification of the key parameters that have an impact on the induced variability. Methods. We analyzed the effect of stellar activity on radial velocities as a function of wavelength by simulating the impact of the properties of spots, shifts induced by convective motions, and rotation. We focused our modeling effort on the active star YZ CMi (GJ 285), which was photometrically and spectroscopically monitored with CARMENES and the Telescopi Joan Oró. Results. We demonstrate that radial velocity curves at different wavelengths yield determinations of key properties of active regions, including spot-filling factor, temperature contrast, and location, thus solving the degeneracy between them. Most notably, our model is also sensitive to convective motions. Results indicate a reduced convective shift for M dwarfs when compared to solar-type stars (in agreement with theoretical extrapolations) and points to a small global convective redshift instead of blueshift. Conclusions. Using a novel approach based on simultaneous chromatic radial velocities and light curves, we can set strong constraints on stellar activity, including an elusive parameter such as the net convective motion effect.

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“…For the Sun as a star, ΔT 500-600 K because sunspot irradiance is dominated by the penumbral regions (cf., e.g., Lanza et al 2004, and references therein). For a star with T = 3750 K, a spot temperature deficit ΔT ≥ 1500 K is required to produce a R s that is comparable to that of a planetary transit, which is also unlikely for such a cool star (see, e.g., Berdyugina 2005;Zboril 2003). …”

Section: Influence Of Stellar Activity On Stellar Colours and The Chamentioning

confidence: 99%

Multiwavelength flux variations induced by stellar magnetic activity: effects on planetary transits

Ballerini

Micela

Lanza

et al. 2012

A&A

102

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Stellar magnetic activity is a source of noise in the study of the transits of extrasolar planets. It induces flux variations that significantly affect the transit depth determination and the derivations of planetary and stellar parameters. Furthermore, the colour dependence of stellar activity may significantly influence the characterization of planetary atmospheres. Here we present a systematic approach to quantify the corresponding stellar flux variations as a function of wavelength bands. We consider a star with spots covering a given fraction of its disc and model the variability in both the UBVRIJHK photometric system and the Spitzer/IRAC wavebands for dwarf stars from G to M spectral types. We compare activity-induced flux variations in different passbands with planetary transits and quantify how they affect the determination of the planetary radius and the analysis of the transmission spectroscopy in the study of planetary atmospheres. We suggest that the monitoring of the systems by using broad-band photometry, from visible to infrared, helps us to constrain activity effects. The ratio of the relative variations in the stellar fluxes at short wavelength optical bands (e.g., U or B) to near-infrared ones (e.g., J or K) can be used to distinguish starspot brightness dips from planetary transits in a stellar light curve. In addition to the perturbations in the measurement of the planetary radius, we find that starspots can affect the determinations of both the relative semimajor axis and the inclination of the planetary orbit, which have a significant impact on the derivation of the stellar density from the transit light curves.

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Spot modelling of the flare M4.5 dwarf YZ CMi

Cited by 15 publications

References 11 publications

BROADBAND TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH GJ 1214b SUGGESTS A LOW MEAN MOLECULAR WEIGHT ATMOSPHERE

BROADBAND TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH GJ 1214b SUGGESTS A LOW MEAN MOLECULAR WEIGHT ATMOSPHERE

The CARMENES search for exoplanets around M dwarfs

Multiwavelength flux variations induced by stellar magnetic activity: effects on planetary transits

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