J/AJ/150/49 Photometry and spectroscopy of HATS-8 (Bayliss+, 2015)
HATS-8b: a low-density transiting Super-Neptune.
Bayliss D., Hartman J.D., Bakos G.A., Penev K., Zhou G., Brahm R.,
Rabus M., Jordan A., Mancini L., de Val-Borro M., Bhatti W., Espinoza N.,
Csubry Z., Howard A.W., Fulton B.J., Buchhave L.A., Henning T., Schmidt B.,
Ciceri S., Noyes R.W., Isaacson H., Marcy G.W., Suc V., Lazar J., Papp I.,
Sari P.
<Astron. J., 150, 49 (2015)>
=2015AJ....150...49B 2015AJ....150...49B (SIMBAD/NED BibCode)
ADC_Keywords: Planets ; Stars, double and multiple ; Photometry ;
Radial velocities ; Stars, dwarfs ; Stars, G-type
Keywords: planetary systems - stars: individual: HATS-8 -
techniques: photometric - techniques: spectroscopic
Abstract:
HATS-8b is a low density transiting super-Neptune discovered as part
of the HATSouth project. The planet orbits its solar-like G-dwarf host
(V=14.03±0.10, Teff=50K) with a period of 3.5839days. HATS-8b is
the third lowest-mass transiting exoplanet to be discovered from a
wide-field ground-based search, and with a mass of 0.138+/0.019MJ it
is approximately halfway between the masses of Neptune and Saturn.
However, HATS-8b has a radius of 0.873+0.123-0.075, resulting in a
bulk density of just 0.259±0.091g/cm3. The metallicity of the host
star is super-solar ([Fe/H]=0.210±0.080), providing evidence against
the idea that low-density exoplanets form from metal-poor
environments. The low density and large radius of HATS-8b results in
an atmospheric scale height of almost 1000km, and in addition to this
there is an excellent reference star of nearly equal magnitude at just
19'' separation in the sky. These factors make HATS-8b an exciting
target for future atmospheric characterization studies, particularly
for long-slit transmission spectroscopy.
Description:
HATS-8 was intensively monitored as part of the HATSouth survey (Bakos
et al., 2013PASP..125..154B 2013PASP..125..154B). Although some data were acquired as
early as 2009 September, the bulk of the observations, over 10000
images, were taken between 2011 March and August. HATSouth employs
Takahashi astrographs (f/2.8, 18cm apertures) imaged onto Apogee U16M
4K*4K cameras. Imaging is performed in the Sloan r-band. Images are
collected from all three sites in the global network (HS-1/G579 on
2009 Sep-2011 Aug, HS-3/G579 on 2010 Mar-2011 Aug, and HS-5/G579 on
2010 Sep-2011 Aug).
Precise photometric observations of a transit of HATS-8b were carried
out using the SiTe3 imaging camera on the SWOPE 1m telescope at Las
Campanas Observatory (LCO) in Chile on 2013 May 29. Defocused imaging
over the 14.8'*22.8' field was performed in the i-band. A second
photometric observation of transits of HATS-8b was obtained with the
1m SWOPE telescope on the night of 2014 July 1. The monitoring was
carried out in the i-band, using the E2V imaging camera. Nine days
later we observed another transit of HATS-8b, this time using Las
Cumbres Observatory Global Telescope Network (LCOGT) 1m telescope
network. This observation was carried out with the LCOGT 1m telescope
at CTIO in Chile using the Sinistro imaging camera in the i-band. The
photometric observations are presented in Table2.
Follow-up spectroscopy was performed in 2012 October using the echelle
spectrograph on the 2.5m du Pont telescope at LCO in Chile. We
obtained two spectra using the 1''*4'' slit (R∼40000) on the nights of
2012 October 25 and 26, each with an exposure time of 1800s. A further
observation of HATS-8 was obtained with the FEROS spectrograph on the
MPG 2.2m telescope on 2013 Jul 18 (R=48000) at the ESO Observatory in
La Silla, Chile.
We observed HATS-8 with the High Resolution Echelle Spectrometer
(HIRES) on Keck I in Hawaii between 2014 June and September. We used
HIRES in its standard configuration for precise radial velocity
measurements: a slit width of 0.86'', λ/Δλ∼55000,
and wavelength coverage of 3800-8000Å. Exposure times were
typically 1500s and achieved a S/N of 40/pixel in the continuum near
5500Å in the reduced HIRES spectra. The radial velocity
measurements are listed in Table4.
Objects:
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RA (ICRS) DE Designation(s) (Period)
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19 39 46.02 -25 44 53.9 HATS-8 = 2MASS J19394601-2544539 (P=3.583893)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 56 10667 Differential photometry of HATS-8
table4.dat 44 9 Relative radial velocities and bisector span
measurements of HATS-8
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See also:
J/AJ/150/33 : Photometry + spectroscopy of HATS-9 and HATS-10 (Brahm+, 2015)
J/AJ/149/166 : Photometry and spectroscopy of HATS-6 (Hartman+, 2015)
J/AJ/145/5 : Follow-up photometry of HATS-1 (Penev+, 2013)
J/AJ/144/139 : HAT-P-39, HAT-P-40, and HAT-P-41 follow-up (Hartman+, 2012)
J/ApJ/742/59 : HAT-P-32 and HAT-P-33 follow-up (Hartman+, 2011)
J/ApJ/728/138 : Follow-up photometry of HAT-P-26 (Hartman+, 2011)
J/ApJ/726/52 : HAT-P-18 and HAT-P-19 follow-up (Hartman+, 2011)
J/ApJ/710/1724 : Follow-up photometry for HAT-P-11 (Bakos+, 2010)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 F11.5 d BJD Barycentric Julian Date (BJD-2400000)
13- 20 F8.5 mag Dmag [-0.06/0.05] Differential magnitude in Filter (1)
22- 28 F7.5 mag e_Dmag [0/0.08] Uncertainty in Dmag
30- 37 F8.5 mag omag [3/15]? Original magnitude in Filter (2)
39 A1 --- Flt [ri] Filter used in observation (Sloan-r or i)
41- 56 A16 --- Inst Instrument used to obtain data (HS=HATSouth,
LCOGT1m/Sinistro, Swope/E2V, Swope/SiTe3) (3)
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Note (1): The out-of-transit level has been subtracted. For the HATSouth light
curve (rows with "HS" in the Inst column), these magnitudes have been
detrended using the EPD and TFA procedures prior to fitting a transit model
to the light curve. Primarily as a result of this detrending, but also due
to blending from neighbors, the apparent HATSouth transit depth is somewhat
shallower than that of the true depth in the Sloan r filter (the apparent
depth is 85% that of the true depth). For the follow-up light curves (rows
with an Instrument other than "HS") these magnitudes have been detrended
with the EPD procedure, carried out simultaneously with the transit fit
(the transit shape is preserved in this process).
Note (2): Raw magnitude values without application of the EPD procedure. This is
only reported for the follow-up light curves.
Note (3): The instruments are defined as below:
LCOGT1m/Sinistro = Las Cumbres Observatory Global Telescope Network (LCOGT)
1m telescope at Cerro Tololo Inter-American Observatory
(CTIO) in Chile using the Sinistro imaging camera;
Swope/SiTe3 = The SiTe3 imaging camera on the SWOPE 1m telescope at
Las Campanas Observatory (LCO) in Chile;
Swope/E2V = 1m SWOPE telescope with the E2V imaging camera.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 d BJD Barycentric Julian Date (BJD-2456000)
11- 16 F6.2 m/s RV [-25.1/17.4] Radial velocity
18- 22 F5.2 m/s e_RV [5.6/12.7] 1σ uncertainty in RV
24- 28 F5.1 m/s BS [-14.8/10]? Bissector Span
30- 33 F4.1 m/s e_BS [5.5/16.4]? 1σ uncertainty in BS
35- 39 F5.3 --- Phase [0.2/0.9] Phase
41- 44 A4 --- Inst Instrument (High Resolution Echelle Spectrometer
(HIRES) on Keck I in Hawaii)
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 24-Nov-2015