ABSTRACT We present the first detection of the photometric variability in a spectroscopically confirmed Y dwarf. The Infrared Array Camera on board the Spitzer Space Telescope was used to obtain time ...series photometry of WISE J140518.39+553421.3 at 3.6 and 4.5 m over a 24-hr period at two different epochs separated by 149 days. Variability is evident at 4.5 m in the first epoch and at 3.6 and 4.5 m in the second epoch, which suggests that the underlying cause or causes of this variability change on the timescales of months. The second-epoch 3.6 and 4.5 light curves are nearly sinusoidal in form, in phase, have periods of roughly 8.5 hr, and have semi-amplitudes of 3.5%. We find that a simple geometric spot model with a single bright spot reproduces these observations well. We also compare our measured semi-amplitudes of the second-epoch light curves to predictions of the static, one-dimensional, partly cloudy, and hot spot models of Morley and collaborators, and find that neither set of models can reproduce the observed 3.6 and 4.5 semi-amplitudes simultaneously. Therefore, more advanced two-dimensional or three-dimensional models that include time-dependent phenomena like vertical mixing, cloud formation, and thermal relaxation are sorely needed in order to properly interpret our observations.
ABSTRACT
We have monitored photometrically the Y0 brown dwarf WISEP J173835.52+273258.9 (W1738) at both near- and mid-infrared wavelengths. This ≲1 Gyr old 400 K dwarf is at a distance of 8 pc and ...has a mass around 5
M
Jupiter
. We observed W1738 using two near-infrared filters at
λ
≈ 1
μ
m,
Y
and
J
, on Gemini Observatory and two mid-infrared filters at
λ
≈ 4
μ
m, 3.6 and 4.5, on the
Spitzer
observatory. Twenty-four hours were spent on the source by
Spitzer
on each of 2013 June 30 and October 30 UT. Between these observations, around 5 hr were spent on the source by Gemini on each of 2013 July 17 and August 23 UT. The mid-infrared light curves show significant evolution between the two observations separated by 4 months. We find that a double sinusoid can be fit to the 4.5 data, where one sinusoid has a period of 6.0 ± 0.1 hr and the other a period of 3.0 ± 0.1 hr. The near-infrared observations suggest variability with a ∼3.0 hr period, although only at a ≲2
σ
confidence level. We interpret our results as showing that the Y dwarf has a 6.0 ± 0.1 hr rotation period, with one or more large-scale surface features being the source of variability. The peak-to-peak amplitude of the light curve at 4.5 is 3%. The amplitude of the near-infrared variability, if real, may be as high as 5%–30%. Intriguingly, this size of variability and the wavelength dependence can be reproduced by atmospheric models that include patchy KCl and Na
2
S clouds and associated small changes in surface temperature. The small number of large features, as well as the timescale for evolution of the features, is very similar to what is seen in the atmospheres of the solar system gas giants.
A Spectroscopic Orbit for the Late-type Be Star β CMi Dulaney, Nicholas A.; Richardson, Noel D.; Gerhartz, Cody J. ...
Astrophysical journal/The Astrophysical journal,
02/2017, Volume:
836, Issue:
1
Journal Article
Peer reviewed
Open access
The late-type Be star β CMi is remarkably stable compared to other Be stars that have been studied. This has led to a realistic model of the outflowing Be disk by Klement et al. These results showed ...that the disk is likely truncated at a finite radius from the star, which Klement et al. suggest is evidence for an unseen binary companion in orbit. Here we report on an analysis of the Ritter Observatory spectroscopic archive of β CMi to search for evidence of the elusive companion. We detect periodic Doppler shifts in the wings of the H line with a period of 170 days and an amplitude of 2.25 km s−1, consistent with a low-mass binary companion (M 0.42 M ). We then compared small changes in the violet-to-red peak height changes (V/R) with the orbital motion. We find weak evidence that it does follow the orbital motion, as suggested by recent Be binary models by Panoglou et al. Our results, which are similar to those for several other Be stars, suggest that β CMi may be a product of binary evolution where Roche lobe overflow has spun up the current Be star, likely leaving a hot subdwarf or white dwarf in orbit around the star. Unfortunately, no direct sign of this companion star is found in the very limited archive of International Ultraviolet Explorer spectra.
ABSTRACT
The bright and understudied classical Be star HD 6226 has exhibited multiple outbursts in the last several years during which the star grew a viscous decretion disc. We analyse 659 optical ...spectra of the system collected from 2017 to 2020, along with a ultraviolet spectrum from the Hubble Space Telescope and high cadence photometry from both Transiting Exoplanet Survey Satellite (TESS) and the Kilodegree Extremely Little Telescope (KELT) survey. We find that the star has a spectral type of B2.5IIIe, with a rotation rate of 74 per cent of critical. The star is nearly pole-on with an inclination of 13${_{.}^{\circ}}$4. We confirm the spectroscopic pulsational properties previously reported, and report on three photometric oscillations from KELT photometry. The outbursting behaviour is studied with equivalent width measurements of H α and H β, and the variations in both of these can be quantitatively explained with two frequencies through a Fourier analysis. One of the frequencies for the emission outbursts is equal to the difference between two photometric oscillations, linking these pulsation modes to the mass ejection mechanism for some outbursts. During the TESS observation time period of 2019 October 7 to 2019 November 2, the star was building a disc. With a large data set of H α and H β spectroscopy, we are able to determine the time-scales of dissipation in both of these lines, similar to past work on Be stars that has been done with optical photometry. HD 6226 is an ideal target with which to study the Be disc-evolution given its apparent periodic nature, allowing for targeted observations with other facilities in the future.
ABSTRACT We have monitored photometrically the Y0 brown dwarf WISEP J173835.52+273258.9 (W1738) at both near- and mid-infrared wavelengths. This 1 Gyr old 400 K dwarf is at a distance of 8 pc and has ...a mass around 5 MJupiter. We observed W1738 using two near-infrared filters at λ 1 m, Y and J, on Gemini Observatory and two mid-infrared filters at λ 4 m, 3.6 and 4.5, on the Spitzer observatory. Twenty-four hours were spent on the source by Spitzer on each of 2013 June 30 and October 30 UT. Between these observations, around 5 hr were spent on the source by Gemini on each of 2013 July 17 and August 23 UT. The mid-infrared light curves show significant evolution between the two observations separated by 4 months. We find that a double sinusoid can be fit to the 4.5 data, where one sinusoid has a period of 6.0 0.1 hr and the other a period of 3.0 0.1 hr. The near-infrared observations suggest variability with a ∼3.0 hr period, although only at a 2 confidence level. We interpret our results as showing that the Y dwarf has a 6.0 0.1 hr rotation period, with one or more large-scale surface features being the source of variability. The peak-to-peak amplitude of the light curve at 4.5 is 3%. The amplitude of the near-infrared variability, if real, may be as high as 5%-30%. Intriguingly, this size of variability and the wavelength dependence can be reproduced by atmospheric models that include patchy KCl and Na2S clouds and associated small changes in surface temperature. The small number of large features, as well as the timescale for evolution of the features, is very similar to what is seen in the atmospheres of the solar system gas giants.
We have monitored photometrically the Y0 brown dwarf WISEP J173835.52+273258.9 (W1738) at both near- and mid-infrared wavelengths. This . 1 Gyr-old 400 K dwarf is at a distance of 8 pc and has a mass ...around 5 MJupiter. We observed W1738 using two near-infrared lters at 1 m, Y and J, on Gemini observatory, and two mid-infrared lters at 4 m, 3.6 and 4.5, on the Spitzer observatory. Twenty-four hours were spent on the source by Spitzer on each of June 30 and October 30 2013 UT. Between these observations, around 5 hours were spent on the source by Gemini on each of July 17 and August 23 2013 UT. The mid-infrared light curves show signi cant evolution between the two observations separated by four months. We nd that a double sinusoid can be t to the 4.5 data, where one sinusoid has a period of 6:0 0:1 hours and the other a period of 3:0 0:1 hours. The near-infrared observations suggest variability with a 3:0 hour period, although only at a . 2 con dence level. We interpret our results as showing that the Y dwarf has a 6:0 0:1 hour rotation period, with one or more large-scale surface features being the source of variability. The peak-to-peak amplitude of the light curve at 4.5 is 3%. The amplitude of the near-infrared variability, if real, may be as high as 5 to 30%. Intriguingly, this size of variability and the wavelength dependence can be reproduced by atmospheric models that include patchy KCl and Na2S clouds and associated small changes in surface temperature. The small number of large features, and the timescale for evolution of the features, is very similar to what is seen in the atmospheres of the solar system gas giants.
The bright and understudied classical Be star HD 6226 has exhibited multiple outbursts in the last several years during which the star grew a viscous decretion disk. We analyze 659 optical spectra of ...the system collected from 2017-2020, along with a UV spectrum from the Hubble Space Telescope and high cadence photometry from both TESS and the KELT survey. We find that the star has a spectral type of B2.5IIIe, with a rotation rate of 74% of critical. The star is nearly pole-on with an inclination of \(13.4\) degree. We confirm the spectroscopic pulsational properties previously reported, and report on three photometric oscillations from KELT photometry. The outbursting behavior is studied with equivalent width measurements of H\(\alpha\) and H\(\beta\), and the variations in both of these can be quantitatively explained with two frequencies through a Fourier analysis. One of the frequencies for the emission outbursts is equal to the difference between two photometric oscillations, linking these pulsation modes to the mass ejection mechanism for some outbursts. During the TESS observation time period of 2019 October 7 to 2019 November 2, the star was building a disk. With a large dataset of H\(\alpha\) and H\(\beta\) spectroscopy, we are able to determine the timescales of dissipation in both of these lines, similar to past work on Be stars that has been done with optical photometry. HD 6226 is an ideal target with which to study the Be disk-evolution given its apparent periodic nature, allowing for targeted observations with other facilities in the future.
The late-type Be star $\beta$ CMi is remarkably stable compared to other Be
stars that have been studied. This has led to a realistic model of the
outflowing Be disk by Klement et al. These results ...showed that the disk is
likely truncated at a finite radius from the star, which Klement et al.~suggest
is evidence for an unseen binary companion in orbit. Here we report on an
analysis of the Ritter Observatory spectroscopic archive of $\beta$ CMi to
search for evidence of the elusive companion. We detect periodic Doppler shifts
in the wings of the H$\alpha$ line with a period of 170 d and an amplitude of
2.25 km s$^{-1}$, consistent with a low-mass binary companion ($M\approx 0.42
M_\odot$). We then compared the small changes in the violet-to-red peak height
changes ($V/R$) with the orbital motion. We find weak evidence that it does
follow the orbital motion, as suggested by recent Be binary models by Panoglou
et al. Our results, which are similar to those for several other Be stars,
suggest that $\beta$ CMi may be a product of binary evolution where Roche lobe
overflow has spun up the current Be star, likely leaving a hot subdwarf or
white dwarf in orbit around the star. Unfortunately, no direct sign of this
companion star is found in the very limited archive of {\it International
Ultraviolet Explorer} spectra.
We present the first detection of photometric variability of a spectroscopically-confirmed Y dwarf. The Infrared Array Camera on board the Spitzer Space Telescope was used to obtain times series ...photometry at 3.6 and 4.5 microns over a twenty four hour period at two different epochs separated by 149 days. Variability is evident at 4.5 um in the first epoch and at 3.6 and 4.5 um in the second epoch which suggests that the underlying cause or causes of this variability change on the timescales of months. The second-epoch 3.6 and 4.5 light curves are nearly sinusoidal in form, in phase, have periods of roughly 8.5 hours, and have semi-amplitudes of 3.5%. We find that a simple geometric spot model with a single bright spot reproduces these observations well. We also compare our measured semi-amplitudes of the second epoch light curves to predictions of the static, one-dimensional, partly cloudy and hot spot models of Morley and collaborators and find that neither set of models can reproduce the observed 3.6 and4.5 semi-amplitudes simultaneously. More advanced two- or three-dimensional models that include time-dependent phenomena like vertical mixing, cloud formation, and thermal relaxation are therefore sorely needed in order to properly interpret our observations.
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