HATS9-b AND HATS10-b: TWO COMPACT HOT JUPITERS IN FIELD 7 OF THE K2 MISSION^*

HATS-9 and HATS-10 were identified as transiting planetary host candidates after obtaining ∼10,000 images of the same field with three stations on the three HATSouth observing sites. The number of photometric observations that were taken for each star on each of the HATSouth stations is indicated in Table 1, where it can be seen that in both cases ∼45% of the observations came from the HATSouth station located at Las Campanas Observatory (LCO).

Table 1.  Summary of Photometric Observations

Instrument/Fielda	Date(s)	# Images	Cadenceb	Filter	Precisionc
			(s)		(mmag)
HATS-9
HS-1/G579	2010 Mar–2011 Aug	4317	300	$r$ band	6.9
HS-3/G579	2010 Mar–2011 Aug	2138	303	$r$ band	7.6
HS-5/G579	2010 Sep–2011 Aug	2784	303	$r$ band	6.9
FTS	2013 Apr 11	134	80	$i$ band	1.4
PEST	2013 May 31	186	130	${R}_{C}$ band	3.4
HATS-10
HS-1/G579	2009 Sep–2011 Aug	4389	301	$r$ band	7.3
HS-3/G579	2010 Mar–2011 Aug	2596	303	$r$ band	7.2
HS-5/G579	2011 Mar–2011 Aug	3297	303	$r$ band	7.8
CTIO 0.9 m	2012 Aug 29	69	213	$z$ band	2.3
FTS	2013 Apr 05	142	63	$i$ band	4.3
GROND	2013 Jun 14	92	156	$g$ band	0.8
GROND	2013 Jun 14	88	156	$r$ band	1.3
GROND	2013 Jun 14	94	156	$i$ band	0.7
GROND	2013 Jun 14	89	156	$z$ band	0.8
PEST	2013 Jun 27	145	130	${R}_{C}$ band	4.6

Note.

^aFor the HATSouth data we list the HATSouth unit and field name from which the observations are taken. HS-1 and -2 are located at LCO in Chile, HS-3 and -4 are located at the H.E.S.S. site in Namibia, and HS-5 and -6 are located at Siding Spring Observatory in Australia. Each field corresponds to one of 838 fixed pointings used to cover the full 4π celestial sphere. All data from a given HATSouth field are reduced together, while detrending through External Parameter Decorrelation (EPD) is done independently for each unique field+unit combination. ^bThe median time between consecutive images rounded to the nearest second. Due to weather, the day–night cycle, guiding and focus corrections, and other factors, the cadence is only approximately uniform over short timescales. ^cThe rms of the residuals from the best-fit model.

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The HATSouth observations consist of four-minute Sloan r-band exposures obtained with 24 Takahashi E180 astrographs (18 cm aperture) coupled to Apogee 4K × 4K U16M ALTA CCDs. Readout times are of the order of one minute, which results in a cadence of about 5 minutes. Detailed descriptions of the image processing steps and the candidate identification procedures of the HATSouth data can be found in Bakos et al. (2013) and Penev et al. (2013). Briefly, after applying aperture photometry on the images, the light curves generated are detrended using external parameter decorrelation (EPD) and a trend-filtering algorithm (TFA; Kovács et al. 2005). Periodic transits on the detrended light curves are then searched using a box-fitted least squares algorithm (Kovács et al. 2002).

Figure 1 shows the phase-folded detection light curves of HATS-9b and HATS-10b, where a clear ∼10 mmag flat-bottom transit can be observed in both cases.

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Transit-like light curves can be produced by different configurations of stellar binaries. Spectroscopic observations are required to reject false positives and to obtain the orbital parameters and masses of the true planets. Due to the great number of HATSouth candidates and the limited available observing time at spectroscopic facilities, this follow-up is performed in a two-step procedure as we now describe. All spectroscopic observations are summarized in Table 2.

Table 2.  Summary of Spectroscopy Observations

Instrument	UT Date(s)	# Spec.	Res.	S/N Rangea	${\gamma }_{\mathrm{RV}}$ b	RV Precisionc
			${\rm{\Delta }}\lambda$/λ/1000		($\mathrm{km}\;{{\rm{s}}}^{-1}$)	(${\rm{m}}\;{{\rm{s}}}^{-1}$)
HATS-9
APO 3.5 m/ARCES	2012 Aug 25	1	31.5	27	−11.5	500
ANU 2.3 m/WiFeS	2012 Sep 8	1	3	140	⋯	⋯
Euler 1.2 m/Coralie	2012 Nov 6–10	4	60	14–20	−10.634	37
MPG 2.2 m/FEROS	2012 Aug–2013 May	9	48	32–76	−10.653	32
Subaru 8 m/HDS	2012 Sep 19	3	60	100–114	⋯	⋯
Subaru 8 m/HDS+I2	2012 Sep 20–22	9	60	60–100	⋯	11
HATS-10
du Pont 2.5 m/Echelle	2013 Aug 21	1	40	48	−29.2	500
Euler 1.2 m/Coralie	2012 Aug–2013 Aug	12	60	17–23	−28.131	68
MPG 2.2 m/FEROS	2013 Mar–Jul	5	48	29–85	−28.044	50
Subaru 8 m/HDS	2012 Sep 22	3	60	74–94	⋯	⋯
Subaru 8 m/HDS+I2	2012 Sep 19–21	9	60	41–99	⋯	14

Note.

^aS/N per resolution element near 5180 Å. ^bFor Coralie and FEROS this is the systemic RV from fitting an orbit to the observations in Section 3.3. For ARCES and the du Pont Echelle it is the measured RV of the single observation. We do not provide this quantity for instruments for which only relative RVs are measured, or for WiFeS, which was only used to measure stellar atmospheric parameters. ^cFor high-precision RV observations included in the orbit determination, this is the RV residual from the best-fit orbit; for other instruments used for reconnaissance spectroscopy this is an estimate of the precision.

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First, initial spectra are acquired (with either low resolution or low signal-to-noise ratio (S/N)) to make a rough estimation of the stellar parameters, identifying spectra composed of more than one star, and measuring RV variations produced by stellar-mass companions. HATS-9 was observed with WIFeS (Dopita et al. 2007) on the ANU 2.3 m telescope, obtaining ${T}_{\mathrm{eff}\star }$ = 5821 ± 300 K, $\mathrm{log}{g}_{\star }$ = 3.9 ± 0.3, and $[\mathrm{Fe}/{\rm{H}}]$ = 0.5 ± 0.5, and with ARCES on the APO 3.5 m obtaining ${T}_{\mathrm{eff}\star }$ = 5692 ± 50 K, $\mathrm{log}{g}_{\star }$ = 4.14 ± 0.1, and $[\mathrm{Fe}/{\rm{H}}]$ = 0.5 ± 0.08. Both estimates of stellar parameters were consistent with a G-type dwarf, but the subsolar surface gravity value points toward a slightly evolved system. Details on the observing strategy, reduction methods, and the processing of the spectra for WIFeS can be found in Bayliss et al. (2013). The ARCES observation was carried out using the $1\buildrel{\prime\prime}\over{.} 6\times 3\buildrel{\prime\prime}\over{.} 2$ slit, yielding an echelle spectrum with 107 orders covering the wavelength range 3200–10000 Å at a resolution of ${\rm{\Delta }}\lambda /\lambda \;\sim$ 31,500. A single ThAr lamp spectrum was obtained immediately following the science exposure with the telescope still pointed toward HATS-9. The science observation was reduced to a wavelength-calibrated spectrum using the standard IRAF echelle package¹³ and analyzed using the Spectral Parameter Classification program (Buchhave et al. 2012) to determine the radial velocity and stellar atmospheric parameters.

Reconnaissance spectroscopy was performed for HATS-10 using the echelle spectrograph mounted on the du Pont 2.5 m telescope at LCO. One observation using the $1\prime\prime \times 4\prime\prime$ slit (${\rm{\Delta }}\lambda /\lambda \;\sim$ 40,000) was enough to confirm that HATS-10 has a single-lined spectrum with the following stellar parameters: ${T}_{\mathrm{eff}\star }$ = 6100 ± 100 K, $\mathrm{log}{g}_{\star }$ = 4.6 ± 0.5 $[\mathrm{Fe}/{\rm{H}}]$ = 0.0 ± 0.5, $v\mathrm{sin}i$ = 5.0 ± 2.0 km s⁻¹. This spectrum was reduced and analyzed with an automated pipeline developed to deal with data coming from a host of different echelle spectrographs (R. Brahm et al. 2015, in preparation). The pipeline for du Pont is very similar to the ones we have previously detailed for Coralie and FEROS data in Jordán et al. (2014).

Once both candidates were identified as single-lined late-type dwarfs, spectra from high-precision instruments were required to measure RV variations with high precision (<30 m s⁻¹) in order to measure the mass of the substellar companions and obtain the orbital parameters. HATS-9 and HATS-10 were observed several times with Coralie (Queloz et al. 2001) on the 1.2 m Euler telescope, FEROS (Kaufer & Pasquini 1998) on the 2.2 m MPG telescope, and HDS on the 8 m Subaru telescope (Noguchi et al. 2002). Coralie and FEROS data were processed with the pipeline described in Jordán et al. (2014), where RV values are obtained using the cross-correlation technique against a binary mask, and bisector span (BS) measurements are computed from the cross-correlation peak following Queloz et al. (2001). HDS RVs were measured using the procedure detailed in Sato et al. (2002, 2012), which are in turn based on the method of Butler et al. (1996), while BS values were obtained following Bakos et al. (2007).

Phased high-precision RV and BS measurements are shown for each system in Figure 2 and the data are listed in Table 3. Both candidates show RV variations in phase with photometric ephemeris; however, for HATS-10 the residuals are higher than expected. This deviation can be partly explained by moonlight contamination in five spectra acquired with Coralie in 2013 August, which are marked with crosses in Figure 2. There are no significant correlations between the RV and BS variations and thus we conclude the RV variations are not produced by stellar activity. The 95% confidence interval for the Pearson correlation coefficient between RV and BS was computed for both candidates using a bootstrap procedure. The confidence intervals are [−0.57, 0.07] and [−0.43, 0.37] for HATS-9 and HATS-10, respectively. The individual FEROS spectra were median combined for both candidates to perform a precise estimation of the stellar parameters.

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Table 3.  Relative Radial Velocities and Bisector Spans for HATS-9 and HATS-10

BJD	RVa	σRVb	BS	σBS	Phase	Instrument
(2,456,000+)	(${\rm{m}}\;{{\rm{s}}}^{-1}$)	(${\rm{m}}\;{{\rm{s}}}^{-1}$)	(${\rm{m}}\;{{\rm{s}}}^{-1}$)	(${\rm{m}}\;{{\rm{s}}}^{-1}$)
HATS-9
169.62456	82.24	28.00	−126.0	13.0	0.686	FEROS
171.51911	107.24	26.00	−66.0	13.0	0.675	FEROS
173.70707	67.24	37.00	−93.0	17.0	0.817	FEROS
189.85616	...	...	−3.6	13.0	0.249	Subaru
189.87089	...	...	−2.3	11.0	0.257	Subaru
189.88561	...	...	9.6	9.2	0.264	Subaru
190.84576	129.27	7.39	6.2	13.4	0.766	Subaru
190.86048	146.04	8.17	5.3	10.0	0.773	Subaru
190.87520	134.32	7.39	−6.7	13.6	0.781	Subaru
191.84685	−139.82	13.91	−9.6	21.4	0.288	Subaru
191.86157	−133.96	12.35	6.0	13.5	0.296	Subaru
191.87633	−112.04	12.85	19.1	21.9	0.304	Subaru
192.84272	112.22	8.57	−3.7	18.5	0.808	Subaru
192.85745	126.06	10.89	−28.3	16.3	0.816	Subaru
192.87217	100.81	9.05	8.0	8.8	0.824	Subaru
205.55663	−48.76	22.00	2.0	11.0	0.446	FEROS
213.50471	74.24	24.00	6.0	12.0	0.596	FEROS
215.55235	125.24	30.00	−31.0	14.0	0.665	FEROS
219.55921	172.24	23.00	−3.0	12.0	0.757	FEROS
237.50625	−67.84	28.00	41.0	22.0	0.128	Coralie
238.50417	86.16	31.00	157.0	24.0	0.649	Coralie
239.50502	−141.84	36.00	16.0	24.0	0.171	Coralie
241.53678	−82.84	64.00	349.0	32.0	0.232	Coralie
424.89567	64.24	36.00	66.0	17.0	0.965	FEROS
427.91875	7.24	45.00	−20.0	20.0	0.544	FEROS
HATS-10
160.60805	−132.00	28.00	−68.0	21.0	0.267	Coralie
161.58511	−77.00	34.00	29.0	22.0	0.561	Coralie
164.61796	−98.00	33.00	12.0	22.0	0.477	Coralie
189.90597	−27.97	14.29	−6.1	27.3	0.110	Subaru
189.92069	−42.32	22.31	...	...	0.115	Subaru
189.93541	−34.14	35.70	...	...	0.119	Subaru
190.89115	−35.74	13.59	17.7	38.3	0.408	Subaru
190.90587	−24.73	14.10	10.6	18.6	0.412	Subaru
190.92060	−26.35	14.32	−17.0	25.1	0.416	Subaru
191.89225	49.44	23.96	3.2	15.3	0.710	Subaru
191.90697	62.06	24.16	0.2	17.3	0.714	Subaru
191.92170	46.62	38.06	...	...	0.719	Subaru
192.88724	...	...	−34.5	31.0	0.010	Subaru
192.89965	...	...	−0.2	23.1	0.014	Subaru
192.91206	...	...	25.9	15.7	0.018	Subaru
237.55535	−46.00	46.00	123.0	24.0	0.493	Coralie
238.55388	70.00	37.00	−24.0	22.0	0.795	Coralie
239.53128	−108.00	46.00	−37.0	24.0	0.090	Coralie
241.51608	177.00	52.00	67.0	26.0	0.689	Coralie
375.90634	−44.76	23.00	16.0	12.0	0.255	FEROS
376.90643	47.24	24.00	37.0	12.0	0.557	FEROS
377.90816	109.24	24.00	56.0	12.0	0.860	FEROS
427.83173	108.24	51.00	114.0	22.0	0.929	FEROS
491.79404	−123.76	20.00	14.0	10.0	0.236	FEROS
524.51947c	−98.00	29.00	249.0	21.0	0.115	Coralie
524.59002c	−59.00	25.00	196.0	19.0	0.136	Coralie
524.70382c	−75.00	29.00	315.0	21.0	0.170	Coralie
525.53878c	57.00	39.00	462.0	24.0	0.422	Coralie
525.65573c	−103.00	38.00	459.0	24.0	0.458	Coralie

Note. Note that for the iodine-free template exposures we do not measure the RV but do measure the BS and S indexes. Such template exposures can be distinguished by the missing RV value. The Subaru/HDS observations of HATS-10 without BS measurements have too low S/N in the I₂-free blue spectral region to pass our quality threshold for calculating accurate BS values.

^aThe zero point of these velocities is arbitrary. An overall offset ${\gamma }_{\mathrm{rel}}$ fitted independently to the velocities from each instrument has been subtracted. ^bInternal errors excluding the component of astrophysical jitter are considered in Section 3.3. ^cCoralie observations acquired in 2013 August were contaminated with moonlight.

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In order to confirm the occurrence of the transits and to better constrain the orbital and physical parameters of the companions, higher precision light curves for both candidates were acquired using several telescopes around the globe. Table 1 summarizes the key aspects of this photometric follow-up, including the dates of the observations, the cadence, and the filter.

Two partial transits of HATS-9 were detected using the 0.3 m Perth Exoplanet Survey Telescope (PEST) and the spectral camera on the 2 m Faulkes Telescope South (FTS), part of Las Cumbres Observatory Global Telescope (LCOGT). Results of these observations are presented in Table 4 and shown in Figure 3. Two partial transits of HATS-10 were observed with FTS and the CTIO 0.9 m telescope. Another two full transits were measured with PEST and the GROND instrument on the MPG 2.2 m. These HATS-10 light curves are shown in Figure 4. All facilities used for high-precision photometric follow-up have been previously used by HATSouth; the instrument specifications, observation strategies, and reduction procedures adopted can be found in Bayliss et al. (2013), Zhou et al. (2014b), Hartman et al. (2014), and Mohler-Fischer et al. (2013) for FTS, PEST, CTIO 0.9 m, and GROND, respectively.

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We determine precise stellar parameters for HATS-9 and HATS-10 using a new code called ZASPE (Zonal Atmospherical Stellar Parameter Estimator) on median combined FEROS spectra. The detailed structure and performance of ZASPE will be presented elsewhere (Brahm et al., in preparation), but in summary ZASPE is a Python-based code that computes the χ² between the observed spectra and the PHOENIX grid of synthetic spectra (Husser et al. 2013) only in the spectral zones most sensitive to each stellar parameter. The optimal set of stellar parameters (${T}_{\mathrm{eff}\star }$, $\mathrm{log}{g}_{\star }$, $[\mathrm{Fe}/{\rm{H}}]$, and $v\mathrm{sin}i$) is found iteratively and the sensitive zones are determined in each iteration. One of the most novel features of ZASPE is that the errors on the stellar parameters are computed from the data itself and include the systematic mismatches between the observations and the best fitted model. We have validated the results of ZASPE against a set of stars with interferometrically determined stellar parameters (Boyajian et al. 2012) that have publicly available FEROS spectra. Results of this comparison are shown in Figure 5. The resulting parameters for HATS-9 are ${T}_{\mathrm{eff}\star }$ = 5363 ± 90 K, $\mathrm{log}{g}_{\star }$ = 3.97 ± 0.2, $[\mathrm{Fe}/{\rm{H}}]$ = 0.33 ± 0.09, and $v\mathrm{sin}i$ = 4.67 ± 0.5 km s⁻¹, while for HATS-10 we obtain ${T}_{\mathrm{eff}\star }$ = 5974 ± 110 K, $\mathrm{log}{g}_{\star }$ = 4.44 ± 0.13, $[\mathrm{Fe}/{\rm{H}}]$ = 0.19 ± 0.07, and $v\mathrm{sin}i$ = 5.66 ± 0.5 km s⁻¹.

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These sets of stellar parameters were refined using the information contained in the transit light curves. The stellar mean density (${\rho }_{\star }$) can be computed directly from one of the light-curve model parameters ($a/{R}_{\star }$) and the period and eccentricity of the orbit using Kepler's third law with only a slight dependence on the stellar parameters through the limb-darkening coefficients (Sozzetti et al. 2007). The spectroscopically determined ${T}_{\mathrm{eff}\star }$ and $[\mathrm{Fe}/{\rm{H}}]$ were coupled with ${\rho }_{\star }$ and Yonsei–Yale stellar evolution models (Y2; Yi et al. 2001) to determine the stellar physical parameters (${R}_{\star }$, ${M}_{\star }$, and the age of the star), which were used to compute a new and more precise estimation of $\mathrm{log}{g}_{\star }$ for HATS-9 ($\mathrm{log}{g}_{\star }$ = 4.12 ± 0.04) and HATS-10 ($\mathrm{log}{g}_{\star }$ = 4.38 ± 0.03). A new set of ${T}_{\mathrm{eff}\star }$, $[\mathrm{Fe}/{\rm{H}}]$, and $v\mathrm{sin}i$ was determined using ZASPE with $\mathrm{log}{g}_{\star }$ fixed to the precise values obtained by modeling the light curves, followed by a new estimation of ${\rho }_{\star }$ and a new modeling of stellar isochrones. The new set of stellar parameters fixing $\mathrm{log}{g}_{\star }$, which are the ones we adopted for further analysis, were consistent with the initial values quoted in the previous paragraph and are listed in Table 5, where distances are determined by comparing the measured broadband photometry listed in that table to the predicted magnitudes in each filter from the isochrones. We assume a ${R}_{V}=3.1$ extinction law from Cardelli et al. (1989) to determine the extinction. The 1σ and 2σ confidence ellipsoids in ${T}_{\mathrm{eff}\star }$ and ${\rho }_{\star }$ are plotted in Figure 6 for both planet hosts, along with the Y2 isochrones for the ZASPE determined $[\mathrm{Fe}/{\rm{H}}]$. We find that HATS-9 is a $1.030\pm 0.039$ M_⊙, ${1.503}_{-0.043}^{+0.101}$ R_⊙, quite evolved ($10.8\pm 1.5$ Gyr) star, while HATS-10 is a $1.101\pm 0.054$ M_⊙, ${1.105}_{-0.040}^{+0.055}$ R_⊙ main-sequence star.

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Table 5.  Stellar Parameters for HATS-9 and HATS-10

	HATS-9	HATS-10
Parameter	Value	Value	Source
Astrometric properties and cross-identifications
2MASS-ID...	2MASS 19231442-2009587	2MASS 19371363-2212161	⋯
GSC-ID...	GSC 6305-02502	GSC 6311-00085	⋯
R.A. (J2000)...	19h23m1428	19h37m1380	2MASS
Dec. (J2000)...	−20°09058.700	−22°12016.100	2MASS
${\mu }_{{\rm{R}}.{\rm{A}}.}$ ($\mathrm{mas}\;{\mathrm{yr}}^{-1}$)	0.3 ± 4.3	3.1 ± 1.3	UCAC4
${\mu }_{\mathrm{Dec}.}$ ($\mathrm{mas}\;{\mathrm{yr}}^{-1}$)	−1.9 ± 2.8	−3.2 ± 1.6	UCAC4
Spectroscopic properties
${T}_{\mathrm{eff}\star }$ (K)...	5366 ± 70	5880 ± 120	ZASPEa
$[\mathrm{Fe}/{\rm{H}}]$...	0.340 ± 0.050	0.15 ± 0.10	ZASPE
$v\mathrm{sin}i$ ($\mathrm{km}\;{{\rm{s}}}^{-1}$)...	4.58 ± 0.90	5.68 ± 0.70	ZASPE
${v}_{\mathrm{mac}}$ ($\mathrm{km}\;{{\rm{s}}}^{-1}$)...	4.6	3.8	Assumedb
${v}_{\mathrm{mic}}$ ($\mathrm{km}\;{{\rm{s}}}^{-1}$)...	1.0	1.0	Assumedc
${\gamma }_{\mathrm{RV}}$ ($\mathrm{km}\;{{\rm{s}}}^{-1}$)...	−10.644 ± 0.013	−28.088 ± 0.024	Coralie,FEROS
Photometric properties
B(mag)...	14.080 ± 0.010	13.820 ± 0.010	APASSd
V (mag)...	13.276 ± 0.010	13.113 ± 0.010	APASSd
g (mag)...	13.629 ± 0.010	13.448 ± 0.010	APASSd
r (mag)...	13.072 ± 0.030	12.967 ± 0.010	APASSd
i (mag)...	12.865 ± 0.010	12.781 ± 0.010	APASSd
J (mag)...	11.885 ± 0.022	11.866 ± 0.024	2MASS
H (mag)...	11.558 ± 0.027	11.568 ± 0.024	2MASS
Ks (mag)...	11.479 ± 0.022	11.511 ± 0.025	2MASS
Derived properties
${M}_{\star }$ (${M}_{\odot }$)...	1.030 ± 0.039	1.101 ± 0.054	YY+${\rho }_{\star }$+ZASPEe
${R}_{\star }$ (${R}_{\odot }$)...	${1.503}_{-0.043}^{+0.101}$	${1.105}_{-0.040}^{+0.055}$	YY+${\rho }_{\star }$+ZASPE
$\mathrm{log}{g}_{\star }$ (cgs)...	4.095 ± 0.038	4.392 ± 0.032	YY+${\rho }_{\star }$+ZASPE
${\rho }_{\star }$ (${\rm{g}}\;{\mathrm{cm}}^{-3}$)...	${0.427}_{-0.070}^{+0.030}$	${1.15}_{-0.16}^{+0.12}$	YY+${\rho }_{\star }$+ZASPEf
${L}_{\star }$ (${L}_{\odot }$)...	${1.70}_{-0.16}^{+0.24}$	1.31 ± 0.18	YY+${\rho }_{\star }$+ZASPE
MV (mag)...	4.33 ± 0.15	4.52 ± 0.16	YY+${\rho }_{\star }$+ZASPE
MK (mag, ESO)...	2.49 ± 0.13	3.05 ± 0.10	YY+${\rho }_{\star }$+ZASPE
Age (Gyr)...	10.8 ± 1.5	3.3 ± 1.7	YY+${\rho }_{\star }$+ZASPE
AV (mag)...	0.000 ± 0.011	0.112 ± 0.075	YY+${\rho }_{\star }$+ZASPE
Distance (pc)...	${622}_{-30}^{+42}$	496 ± 24	YY+${\rho }_{\star }$+ZASPE

Note.

^aZASPE = Zonal Atmospheric Stellar Parameters Estimator routine for the analysis of high-resolution spectra (R. Brahm et al. 2015, in preparation), applied to the FEROS spectra of HATS-9 and HATS-10. These parameters rely primarily on ZASPE, but have a small dependence also on the iterative analysis incorporating the isochrone search and global modeling of the data, as described in the text ^bComputed following Valenti & Fischer (2005). ^cHusser et al. (2013). ^dFrom APASS DR6 for HATS-9, HATS-10 as listed in the UCAC 4 catalog (Zacharias et al. 2012). ^eYY+${\rho }_{\star }$ + ZASPE = Based on the YY isochrones (Yi et al. 2001), ${\rho }_{\star }$ as a luminosity indicator, and the ZASPE results. ^fIn the case of ${\rho }_{\star }$ the parameter is primarily determined from the global fit to the light curves and RV data. The value shown here also has a slight dependence on the stellar models and ZASPE parameters due to restricting the posterior distribution to combinations of ${\rho }_{\star }$ + ${T}_{\mathrm{eff}\star }$ + $[\mathrm{Fe}/{\rm{H}}]$ that match a YY stellar model.

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We attempted to measure the Lithium absorption line at 6707.8 Å for testing the age estimation of HATS-9, but the quality of our spectra was only enough to rule out a strong absorption feature.

In order to exclude blend scenarios, we carried out a blend analysis of the observations following Hartman et al. (2012). For HATS-9 we find that scenarios involving blends between a stellar eclipsing binary and a foreground or background star can be ruled out with greater than 5σ confidence based on the photometric data alone. The primary constraint in this case is the lack of out-of-transit variations seen in the HATSouth light curve. Due to the short orbital period, the best-fit blend model that reproduces the shape of the transit has a ∼1 mmag amplitude ellipsoidal variation and a ∼0.5 mmag deep secondary eclipse, neither of which are detected in the HATSouth observations. Moreover, the Subaru/HDS observations of HATS-9 show no significant BS variation (the rms scatter of the BS measurements is 12 ${\rm{m}}\;{{\rm{s}}}^{-1}$), providing further evidence that the system is not a blended eclipsing binary. For HATS-10 the photometric observations can be fit by a G+M star eclipsing binary blended with another G star that is slightly brighter than the primary in the eclipsing system. Based on the difference in χ², this model is indistinguishable from a single G star with a transiting planet. We simulated spectra for blend models that could plausibly fit the photometric observations, finding that in all cases the blended systems would have easily been detected as having composite spectra. They also would produce RV and BS variations of several $\mathrm{km}\;{{\rm{s}}}^{-1}$, whereas the observed RV variation is $67\pm 10$ ${\rm{m}}\;{{\rm{s}}}^{-1}$, and the Subaru/HDS BS scatter is only 18 ${\rm{m}}\;{{\rm{s}}}^{-1}$. We conclude that neither HATS-9 nor HATS-10 is a blended eclipsing binary system. As is often the case, however, we are not able to rule out the possibility that either transiting planet system has a fainter stellar-mass companion. For both systems a stellar companion of any mass, up to the mass of the planet-hosting star, is possible. If a massive stellar companion is present in a given system, the true planet radius would be up to ∼60% larger than inferred here. The planet mass would also be larger. High-resolution adaptive optics imaging and/or long-term RV observations are needed to determine whether either system has a stellar companion (e.g., Howell et al. 2012; Horch et al. 2014; Everett et al. 2015).

We modeled the HATSouth photometry, the follow-up photometry, and the high-precision RV measurements following Pál et al. (2008), Bakos et al. (2010), and Hartman et al. (2012). We fit Mandel & Agol (2002) transit models to the light curves, allowing for a dilution of the HATSouth transit depth as a result of blending from neighboring stars and overcorrection by the trend-filtering method. For the follow-up light curves, we include a quadratic trend in time in our model for each event to correct for systematic errors in the photometry. We fit Keplerian orbits to the RV curves, allowing the zero point for each instrument to vary independently in the fit, and allowing for RV jitter, which we we also vary as a free parameter for each instrument.

We used a Differential Evolution Markov Chain Monte Carlo procedure (ter Braak 2006; Eastman et al. 2013) to explore the fitness landscape and to determine the posterior distribution of the parameters.

The resulting parameters for each system are listed in Table 6. HATS-9b has a radius of $1.065\pm 0.098{R}_{{\rm{J}}}$ and a mass of $0.837\pm 0.029{M}_{{\rm{J}}}$, while HATS-10b has a radius of ${0.969}_{-0.045}^{+0.061}{R}_{{\rm{J}}}$ and a mass of $0.526\pm 0.081{M}_{{\rm{J}}}$. Both planets have bulk densities slightly lower than that of Jupiter ($0.85\pm 0.19$ g cm⁻³ and $0.70\pm 0.15$ g cm⁻³, respectively)

Table 6.  Orbital and Planetary Parameters for HATS-9b and HATS-10b

	HATS-9b	HATS-10b
Parameter	Value	Value
Light curve parameters
P (days)	1.9153073 ± 0.0000052	3.3128460 ± 0.0000058
Tc ($\mathrm{BJD}$)a	2456124.25896 ± 0.00086	2456457.88193 ± 0.00022
${T}_{14}$ (days)a	0.1457 ± 0.0024	0.1253 ± 0.0011
${T}_{12}={T}_{34}$ (days)a	0.0106 ± 0.0015	0.01157 ± 0.00100
$a/{R}_{\star }$	${4.36}_{-0.25}^{+0.10}$	${8.73}_{-0.44}^{+0.29}$
$\zeta /{R}_{\star }$ b	14.84 ± 0.26	17.588 ± 0.067
${R}_{{\rm{p}}}/{R}_{\star }$	0.0725 ± 0.0041	0.0903 ± 0.0013
b2	${0.71}_{-0.050}^{+0.112}$	${0.113}_{-0.059}^{+0.087}$
$b\equiv a\mathrm{cos}i/{R}_{\star }$	${0.27}_{-0.12}^{+0.16}$	${0.34}_{-0.10}^{+0.11}$
i (deg)	${86.5}_{-2.5}^{+1.6}$	87.79 ± 0.72
Limb-darkening coefficientsc
${c}_{1},g$ (linear term)	⋯	0.5380
${c}_{2},g$ (quadratic term)	⋯	0.2487
${c}_{1},r$	0.4688	0.3459
${c}_{2},r$	0.2596	0.3349
${c}_{1},i$	0.3533	0.2587
${c}_{2},i$	0.2892	0.3388
${c}_{1},z$	⋯	0.1978
${c}_{2},z$	⋯	0.3360
${c}_{1},R$	0.4369	0.3216
${c}_{2},R$	0.2687	0.3371
RV parameters
K (${\rm{m}}\;{{\rm{s}}}^{-1}$)	133.5 ± 3.4	67 ± 10
ed	<0.129	<0.501
RV jitter HDS (${\rm{m}}\;{{\rm{s}}}^{-1}$)e	0.1 ± 5.2	0.00 ± 0.53
RV jitter FEROS (${\rm{m}}\;{{\rm{s}}}^{-1}$)	0.0 ± 1.7	38 ± 28
RV jitter Coralie (${\rm{m}}\;{{\rm{s}}}^{-1}$)	0.0 ± 1.1	45 ± 23
Planetary parameters
${M}_{{\rm{p}}}$ (${M}_{{\rm{J}}}$)	0.837 ± 0.029	0.526 ± 0.081
${R}_{{\rm{p}}}$ (${R}_{{\rm{J}}}$)	1.065 ± 0.098	${0.969}_{-0:045}^{+0:061}$
$C({M}_{{\rm{p}}},{R}_{{\rm{p}}})$ f	0.48	0.02
${\rho }_{{\rm{p}}}$ (${\rm{g}}\;{\mathrm{cm}}^{-3}$)	0.85 ± 0.19	0.70 ± 0.15
$\mathrm{log}{g}_{{\rm{p}}}$ (cgs)	3.253 ± 0.068	3.140 ± 0.082
a (AU)	0.03048 ± 0.00038	0.04491 ± 0.00074
${T}_{\mathrm{eq}}$ (K)	${1823}_{-35}^{+52}$	1407 ± 39
Θ g	0.0460 ± 0.0039	0.0440 ± 0.0071
${\mathrm{log}}_{10}\langle F\rangle$ (cgs)h	${9.397}_{-0:033}^{+0:049}$	8.947 ± 0.047

Note.

^aTimes are in Barycentric Julian Date calculated directly from UTC without correction for leap seconds. ${T}_{c}$: reference epoch of mid-transit that minimizes the correlation with the orbital period. ${T}_{14}$: total transit duration, time between first to last contact; ${T}_{12}={T}_{34}$: ingress/egress time, time between first and second or third and fourth contact. ^bReciprocal of the half duration of the transit used as a jump parameter in our MCMC analysis in place of $a/{R}_{\star }$. It is related to $a/{R}_{\star }$ by the expression $\zeta /{R}_{\star }=a/{R}_{\star }(2\pi (1+e\mathrm{sin}\omega ))/(P\sqrt{1-{b}^{2}}\sqrt{1-{e}^{2}})$ (Bakos et al. 2010). ^cValues for a quadratic law, adopted from the tabulations by Claret (2004) according to the spectroscopic (ZASPE) parameters listed in Table 5. ^dAs discussed in Section 3.3 the adopted parameters for all four systems are determined assuming circular orbits. We also list the 95% confidence upper limit on the eccentricity determined when $\sqrt{e}\mathrm{cos}\omega$ and $\sqrt{e}\mathrm{sin}\omega$ are allowed to vary in the fit. ^eTerm added in quadrature to the formal RV uncertainties for each instrument. This is treated as a free parameter in the fitting routine. ^fCorrelation coefficient between the planetary mass ${M}_{{\rm{p}}}$ and radius ${R}_{{\rm{p}}}$ estimated from the posterior parameter distribution. ^gThe Safronov number is given by ${\rm{\Theta }}=\frac{1}{2}{({V}_{\mathrm{esc}}/{V}_{\mathrm{orb}})}^{2}=(a/{R}_{{\rm{p}}})({M}_{{\rm{p}}}/{M}_{\star })$ (see Hansen & Barman 2007). ^hIncoming flux per unit surface area, averaged over the orbit.

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Even though HATS-9b and HATS-10b are located in the nominal coordinates of field 7 of K2, only HATS-9b falls on working silicon. A proposal to observe this star in short cadence was recently submitted. The high photometric precision of K2 will allow us to estimate a much more precise radius for HATS-9b, which will help us in determining if this planet is a true outlier in the correlation between planet radius, equilibrium temperature, and planet mass. The high insolation of this planet makes it a very good target for measuring secondary transits and phase curve variations with K2, which will allow us to estimate the albedo and provide a more reliable estimate of its equilibrium temperature. Figure 10 shows a measure of the reflected light signature, ${({R}_{{\rm{P}}}/a)}^{2}$, for hot Jupiters observed by Kepler as a function of planetary radius. From this figure we can see that the potential of detecting reflected light signatures of HATS-9b is high and its amplitude should be similar to that of the giant planets observed by Kepler so far. Other subtle photometric effects, like ellipsoidal variations, Doppler beaming, and the measurement of asteroseismological frequencies, if present, will also be very valuable for the detailed characterization of this particular planet.

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