J/AJ/155/66 Stroemgren photometric observations of GJ 436b (Lothringer+, 2018)
An HST/STIS optical transmission spectrum of warm Neptune GJ 436b.
Lothringer J.D., Benneke B., Crossfield I.J.M., Henry G.W., Morley C.,
Dragomir D., Barman T., Knutson H., Kempton E., Fortney J., McCullough P.,
Howard A.W.
<Astron. J., 155, 66 (2018)>
=2018AJ....155...66L 2018AJ....155...66L (SIMBAD/NED BibCode)
ADC_Keywords: Exoplanets ; Photometry, uvby ; Stars, double and multiple
Keywords: planetary systems - planets and satellites: atmospheres -
planets and satellites: individual (GJ 436b) -
stars: individual (GJ 436) - techniques: spectroscopic
Abstract:
GJ 436b is a prime target for understanding warm Neptune exoplanet
atmospheres and a target for multiple James Webb Space Telescope
(JWST) Guaranteed Time Observation programs. Here, we report the first
space-based optical transmission spectrum of the planet using two
Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph
(STIS) transit observations from 0.53 to 1.03 µm. We find no
evidence for alkali absorption features, nor evidence of a scattering
slope longward of 0.53 µm. The spectrum is indicative of moderate
to high metallicity (∼100-1000x solar), while moderate-metallicity
scenarios (∼100x solar) require aerosol opacity. The optical spectrum
also rules out some highly scattering haze models. We find an increase
in transit depth around 0.8 µm in the transmission spectra of three
different sub-Jovian exoplanets (GJ 436b, HAT-P-26b, and GJ 1214b).
While most of the data come from STIS, data from three other instruments
may indicate this is not an instrumental effect. Only the transit
spectrum of GJ 1214b is well fit by a model with stellar plages on the
photosphere of the host star. Our photometric monitoring of the host
star reveals a stellar rotation rate of 44.1 days and an activity
cycle of 7.4 years. Intriguingly, GJ 436 does not become redder as it
gets dimmer, which is expected if star spots were dominating the
variability. These insights into the nature of the GJ 436 system help
refine our expectations for future observations in the era of JWST,
whose higher precision and broader wavelength coverage will shed light
on the composition and structure of GJ 436b's atmosphere.
Description:
GJ 436 (M2.5V) has been monitored in Stroemgren b and y filters for
the past 14 years using the Tennessee State University's T12 0.8 m
Automatic Photoelectric Telescope (APT) at Fairborn Observatory in
southern Arizona (Henry 1999PASP..111..845H 1999PASP..111..845H; Eaton et al.
2003ASSL..288..189E 2003ASSL..288..189E; Henry & Winn 2008AJ....135...68H 2008AJ....135...68H) in order to
better characterize the star and how star spots may affect our transit
observations. In these observations, we nod the telescope between
GJ 436 and comparison stars of comparable or greater brightness; we
use these stars to remove extinction and seeing effects. Of the three
comparison stars analyzed, HD 102555 (hereafter C1) and HD 103676 (C2)
were the most constant, with very little variation between them over
the 14 years. The third star, HD 99518, showed a gradual brightening
throughout the 14 years of observations. Altogether we have obtained
1735 measurements, which we present in Table 1.
Objects:
-------------------------------------------------
RA (ICRS) DE Designation(s)
-------------------------------------------------
11 42 11.09 +26 42 23.7 GJ 436b = Ross 905b
11 42 11.09 +26 42 23.7 GJ 436 = Ross 905
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . this file
table1.dat 42 1735 Stroemgren photometric observations of GJ 436b
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See also:
J/A+A/471/L51 : Spitzer obs. of the hot Neptune GJ 436b (Gillon+, 2007)
J/A+A/475/1125 : Characterization of the hot Neptune GJ 436b (Demory+, 2007)
J/A+A/486/1039 : HST transit light curve for GJ436b (Bean+, 2008)
J/ApJ/689/L149 : Parameter variations of Gliese 436b transits (Coughlin+, 2008)
J/A+A/507/481 : GJ 436b and XO-1b transits (Caceres+, 2009)
J/ApJ/694/1559 : Photometric follow-up observations of GJ 436b (Shporer+, 2009)
J/ApJ/755/9 : Spitzer/IRAC light curves of GJ 436 system (Stevenson+, 2012)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d BJD Barycentric Julian Date (TDB) (BJD-2400000)
12- 18 F7.5 mag P-C1C2b [4.38585/4.4252] Program star differential
mag in b (1)
20- 26 F7.5 mag P-C1C2y [3.59095/3.6256] Program star differential
mag in y (1)
28- 34 F7.5 mag P-C1C2(b-y) [0.77245/0.8146] Program star differential
mag in (b-y) (1)
36- 42 F7.5 mag P-C1C2(b+y)/2 [3.99265/4.02205] Program star differential
mag in (b+y)/2 (1)
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Note (1): C1C2 demotes the differential magnitude, computed with respect to
the mean brightness of comparison stars C1 (HD 102555) and C2
(HD 103676).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 04-Oct-2018