HATS-54b-HATS-58Ab: five new transiting hot Jupiters including one with a possible temperate companion

TL;DR

This paper reports the discovery of five new transiting hot Jupiters with diverse properties, including one with a potential temperate companion, using the HATSouth survey and Gaia data, highlighting their physical characteristics and possible additional planets.

Contribution

The study presents five newly discovered hot Jupiters, including a candidate temperate companion, with detailed characterization and analysis of their orbital and physical properties, and evidence for an additional planet in the HATS-56 system.

Findings

HATS-54b, HATS-55b, HATS-58Ab are typical short-period hot Jupiters.

HATS-57b is a dense, massive hot Jupiter orbiting an active star.

HATS-56b is a highly inflated hot Jupiter with a potential additional planet.

Abstract

We report the discovery by the HATSouth project of 5 new transiting hot Jupiters (HATS-54b through HATS-58Ab). HATS-54b, HATS-55b and HATS-58Ab are prototypical short period ($P = 2.5-4.2$ days, $R_p\sim1.1-1.2$ $R_J$) hot-Jupiters that span effective temperatures from 1350 K to 1750 K, putting them in the proposed region of maximum radius inflation efficiency. The HATS-58 system is composed of two stars, HATS-58A and HATS-58B, which are detected thanks to Gaia DR2 data and which we account for in the joint modelling of the available data --- with this, we are led to conclude that the hot jupiter orbits the brighter HATS-58A star. HATS-57b is a short-period (2.35-day) massive (3.15 $M_J$) 1.14 $R_J$, dense ($2.65\pm0.21$ g cm$^{-3}$) hot-Jupiter, orbiting a very active star ($2\%$ peak-to-peak flux variability). Finally, HATS-56b is a short period (4.32-day) highly inflated hot-Jupiter (1.7 $R_J$, 0.6 $M_J$), which is an excellent target for future atmospheric follow-up, especially considering the relatively bright nature ($V=11.6$) of its F dwarf host star. This latter exoplanet has another very interesting feature: the radial velocities show a significant quadratic trend. If we interpret this quadratic trend as arising from the pull of an additional planet in the system, we obtain a period of $P_c = 815^{+253}_{-143}$ days for the possible planet HATS-56c, and a minimum mass of $M_c\sin i_c = 5.11 \pm 0.94$ $M_J$. The candidate planet HATS-56c would have a zero-albedo equilibrium temperature of $T_\textrm{eq}=332\pm 50$ K, and thus would be orbiting close to the habitable zone of HATS-56. Further radial-velocity follow-up, especially over the next two years, is needed to confirm the nature of HATS-56c.

Tables

Table 1. Table 1: Summary of photometric observations

Instrument/Fieldaa For HATSouth data we list the HATSouth unit, CCD and field name from which the observations are taken. HS-1 and -2 are located at Las Campanas Observatory 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 unit has 4 ccds. Each field corresponds to one of 838 fixed pointings used to cover the full 4$\pi$ celestial sphere. All data from a given HATSouth field and CCD number are reduced together, while detrending through External Parameter Decorrelation (EPD) is done independently for each unique unit+CCD+field combination.	Date(s)	# Images	Cadencebb The median time between consecutive images rounded to the nearest second. Due to factors such as weather, the day–night cycle, guiding and focus corrections the cadence is only approximately uniform over short timescales.	Filter	Precisioncc The RMS of the residuals from the best-fit model.
			(sec)		(mmag)
HATS-54
HS-2/G700	2011 Apr–2012 Jul	4521	292	$r$	9.8
HS-4/G700	2011 Jul–2012 Jul	3799	301	$r$	10.4
HS-6/G700	2012 Jan–2012 Jul	1425	300	$r$	10.7
Swope 1 m	2016 Feb 09	89	79	$i$	2.2
PEST 0.3 m	2016 Feb 25	169	132	$R_C$	6.3
CHAT 0.7 m	2017 Feb 12	50	222	$i$	2.1
LCO 1 m/SAAO/DomeB	2017 May 10	73	221	$i$	1.7
Swope 1 m	2017 May 30	137	160	$g$	1.9
LCO 1 m/SAAO/DomeC	2017 Jul 05	78	221	$i$	2.2
LCO 1 m/SSO/DomeB	2017 Jul 13	68	224	$i$	3.1
HATS-55
HS-2/G602	2011 Aug–2012 Feb	4192	295	$r$	8.8
HS-4/G602	2011 Aug–2012 Feb	3047	296	$r$	9.3
HS-6/G602	2011 Oct–2012 Feb	1248	303	$r$	8.8
PEST 0.3 m	2015 Feb 14	171	132	$R_C$	5.1
PETS 0.3 m	2015 Mar 03	144	132	$R_C$	4.8
Swope 1 m	2015 Apr 01	250	59	$i$	3.1
LCO 1 m/CTIO/DomeA	2017 Apr 10	69	220	$i$	1.8
LCO 1 m/CTIO/DomeC	2017 Apr 10	69	220	$i$	2.5
HATS-56
HS-4/G698	2015 May–2015 Jul	5	499	$r$	4.7
HS-6/G698	2015 Dec–2016 Jun	4846	343	$r$	6.6
HS-2/G698	2015 Mar–2016 May	2487	352	$r$	4.6
HS-4/G698	2015 Mar–2016 Jun	6851	324	$r$	5.6
HS-6/G698	2015 Mar–2016 Jun	5638	343	$r$	6.1
PEST 0.3 m	2017 Mar 05	182	134	$R_C$	2.0
LCO 1 m/CTIO	2017 Mar 22	139	130	$i$	1.1
LCO 1 m/SSO	2017 Mar 27	47	130	$i$	0.8
HATS-57
HS-1/G548	2014 Sep–2015 Feb	5719	287	$r$	11.5
HS-2/G548	2014 Jun–2015 Apr	7689	348	$r$	10.4
HS-3/G548	2014 Sep–2015 Mar	5214	353	$r$	10.5
HS-4/G548	2014 Jun–2015 Mar	5430	352	$r$	10.6
HS-5/G548	2014 Sep–2015 Mar	5041	359	$r$	10.6
HS-6/G548	2014 Jul–2015 Mar	5989	351	$r$	10.7
CHAT 0.7 m	2017 Aug 28	83	143	$i$	1.3
CHAT 0.7 m	2017 Oct 21	90	146	$i$	1.6
HATS-58
HS-1/G699	2011 Apr–2012 Aug	3645	290	$r$	4.9
HS-3/G699	2011 Jul–2012 Aug	3150	291	$r$	5.7
HS-5/G699	2011 May–2012 Aug	750	290	$r$	4.7
PEST 0.3 m	2017 Mar 09	220	132	$R_C$	2.2
PEST 0.3 m	2017 Apr 20	223	132	$R_C$	2.2
LCO 1 m+SAAO/DomeB	2017 May 15	40	130	$i$	0.7
LCO 1 m+SSO/DomeB	2017 Jul 05	106	134	$i$	2.6

Table 2. Table 2: Summary of spectroscopy observations.

Instrument	UT Date(s)	# Spec.	Res.	S/N Rangeaa S/N per resolution element near 5180 Å.	${\gamma }_{\mathrm{RV}}$bb For high-precision RV observations included in the orbit determination this is the zero-point RV from the best-fit orbit. For other instruments it is the mean value. We do not provide this quantity for the lower resolution WiFeS observations which were only used to measure stellar atmospheric parameters.	RV Precisioncc For high-precision RV observations included in the orbit determination this is the scatter in the RV residuals from the best-fit orbit (which may include astrophysical jitter), for other instruments this is either an estimate of the precision (not including jitter), or the measured standard deviation. We do not provide this quantity for low-resolution observations from the ANU 2.3 m/WiFeS.
			$\Delta \lambda$/$\lambda$/1000		($\mathrm{km}{s}^{-1}$)	($m{s}^{-1}$)
HATS-54
ANU 2.3 m/WiFeS	2014 Jun 3	1	3	26	$\cdots$	$\cdots$
ANU 2.3 m/WiFeS	2014 Jun 3–5	3	7	23–112	42.7	4000
ESO 3.6 m/HARPS	2015 Apr–2017 May	3	115	5–12	46.060	53
MPG 2.2 m/FEROS	2015 Jun–2017 Aug	31	48	17–44	46.127	64
HATS-55
ANU 2.3 m/WiFeS	2014 Dec 13	1	3	60	$\cdots$	$\cdots$
ANU 2.3 m/WiFeS	2014 Dec 29–31	3	7	7–103	-2.3	4000
ESO 3.6 m/HARPS	2015 Feb–Nov	8	115	12–20	-2.919	18
Euler 1.2 m/Coralie	2015 Feb–Mar	4dd We list here the total number of spectra collected for each instrument, including observations that were excluded from the analysis due to very low S/N or substantial sky contamination. For HATS-55 we did not include any of the Coralie observations in the analysis as they had too low RV precision to detect the orbital variation. For HATS-56 and HATS-58 we did not include the single Coralie observations in the analysis.	60	11–14	-2.935	240
HATS-56
MPG 2.2 m/FEROS	2017 Jan–2018 Mar	56	48	24–97	35.740	25
Euler 1.2 m/Coralie	2017 Jan 25	1dd We list here the total number of spectra collected for each instrument, including observations that were excluded from the analysis due to very low S/N or substantial sky contamination. For HATS-55 we did not include any of the Coralie observations in the analysis as they had too low RV precision to detect the orbital variation. For HATS-56 and HATS-58 we did not include the single Coralie observations in the analysis.	60	27	37.99	$\cdots$
ESO 3.6 m/HARPS	2017 Feb 20–22	3	115	21–36	35.730	10
HATS-57
ANU 2.3 m/WiFeS	2017 Jul 11	1	3	30	$\cdots$	$\cdots$
ANU 2.3 m/WiFeS	2017 Jul 11–12	2	7	36–59	-0.5	4000
MPG 2.2 m/FEROS	2017 Jul–Oct	15	48	21–65	0.5455	28
HATS-58
MPG 2.2 m/FEROS	2016 Dec–2017 Mar	11	48	47–91	19.298	58
ANU 2.3 m/WiFeS	2016 Dec 20	1	3	54	$\cdots$	$\cdots$
ANU 2.3 m/WiFeS	2016 Dec 20–22	2	7	52	18.7	4000
Euler 1.2 m/Coralie	2017 Jan 26	1dd We list here the total number of spectra collected for each instrument, including observations that were excluded from the analysis due to very low S/N or substantial sky contamination. For HATS-55 we did not include any of the Coralie observations in the analysis as they had too low RV precision to detect the orbital variation. For HATS-56 and HATS-58 we did not include the single Coralie observations in the analysis.	60	20	19.223	$\cdots$
ESO 3.6 m/HARPS	2017 Feb–Apr	9	115	23–45	19.415	12

Table 3. Table 3: Relative radial velocities and bisector spans for HATS-54–HATS-58.

BJD	RVaa The zero-point of these velocities is arbitrary. An overall offset ${\gamma }_{\mathrm{rel}}$ fitted independently to the velocities from each instrument has been subtracted.	${\sigma }_{\mathrm{RV}}$bb Internal errors excluding the component of astrophysical jitter considered in Section 3.3.	BS	${\sigma }_{\mathrm{BS}}$	Phase	Instrument
(2,450,000$+$)	($m{s}^{-1}$)	($m{s}^{-1}$)	($m{s}^{-1}$)	($m{s}^{-1}$)
HATS-54
$7120.76007$	$68.29$	$19.00$	$15.0$	$31.0$	$0.879$	HARPS
$7181.50030$	$115.34$	$13.00$	$24.0$	$18.0$	$0.753$	FEROS
$7182.69946$	$-196.66$	$15.00$	$-56.0$	$20.0$	$0.225$	FEROS
$7185.49965$	$-133.66$	$14.00$	$-59.0$	$19.0$	$0.325$	FEROS
$7186.66323$	$-50.66$	$23.00$	$14.0$	$30.0$	$0.782$	FEROS
$7187.66100$	$-141.66$	$15.00$	$-50.0$	$20.0$	$0.175$	FEROS
$7195.53227$	$-64.66$	$15.00$	$15.0$	$20.0$	$0.268$	FEROS
$7224.61924$	$126.34$	$23.00$	$157.0$	$30.0$	$0.701$	FEROS
$7228.51247$	$-47.66$	$16.00$	$84.0$	$21.0$	$0.231$	FEROS
$7232.53561$	$6.34$	$21.00$	$40.0$	$25.0$	$0.813$	FEROS
$7887.75568$	$20.19$	$43.10$	$-51.0$	$57.0$	$0.349$	HARPS
$7888.76435$	$161.59$	$59.00$	$6.0$	$77.0$	$0.746$	HARPS
$7903.67827$	$-75.86$	$26.50$	$-84.0$	$34.0$	$0.608$	FEROS
$7905.74906$	$-146.16$	$14.70$	$4.0$	$20.0$	$0.421$	FEROS
$7906.67308$	$180.54$	$12.60$	$3.0$	$18.0$	$0.785$	FEROS
$7907.58913$	$-76.76$	$12.30$	$-129.0$	$17.0$	$0.145$	FEROS
$7908.61270$	$91.74$	$15.10$	$36.0$	$20.0$	$0.547$	FEROS
$7911.51620$	$92.54$	$14.30$	$-33.0$	$19.0$	$0.688$	FEROS
$7913.54999$	$8.84$	$15.30$	$-48.0$	$19.0$	$0.488$	FEROS
$7914.54968$	$103.74$	$13.10$	$-64.0$	$18.0$	$0.881$	FEROS
$7915.61554$	$-104.86$	$12.60$	$-4.0$	$17.0$	$0.299$	FEROS
$7943.48406$	$-63.86$	$11.50$	$-22.0$	$16.0$	$0.253$	FEROS
$7944.53353$	$147.34$	$11.80$	$10.0$	$16.0$	$0.666$	FEROS
$7945.60475$	$7.24$	$14.40$	$-62.0$	$19.0$	$0.087$	FEROS
$7946.50173$	$-43.96$	$12.70$	$50.0$	$18.0$	$0.439$	FEROS
$7948.62577$	$-92.56$	$23.00$	$-24.0$	$28.0$	$0.274$	FEROS
$7949.63156$	$156.44$	$24.60$	$193.0$	$32.0$	$0.670$	FEROS
$7964.52884$	$2.04$	$18.40$	$83.0$	$25.0$	$0.525$	FEROS
$7966.57374$	$-58.46$	$20.10$	$108.0$	$26.0$	$0.329$	FEROS
$7967.50871$	$176.74$	$33.10$	$95.0$	$34.0$	$0.696$	FEROS
$7969.51414$	$35.44$	$18.70$	$-31.0$	$25.0$	$0.485$	FEROS
$7970.52194$	$152.64$	$16.30$	$-82.0$	$22.0$	$0.881$	FEROS
$7971.52200$	$-77.06$	$14.40$	$66.0$	$19.0$	$0.274$	FEROS
$7972.53369$	$135.74$	$15.70$	$26.0$	$20.0$	$0.671$	FEROS

Table 4. Table 5: Stellar parameters for HATS-54–HATS-58A

	HATS-54	HATS-55	HATS-56	HATS-57	HATS-58
Parameter	Value	Value	Value	Value	Value	Source
Astrometric properties and cross-identifications
Gaia DR2-ID	6087996849371141248	5592019557950033536	6144125887172751232	5094406193214399616	6128363666439822208
2MASS-ID	13223237-4441196	07370802-3245195	12003962-4547579	04034760-1903242	12270898-4858423
GSC-ID	GSC 7799-01184	GSC 7109-00596	GSC 8229-02228	GSC 5885-00663	GSC 8239-00065
R.A. (J2000)	${13}^h{22}^{m}32.3724s$	${07}^h{37}^{m}08.0194s$	${12}^h{00}^{m}39.6300s$	${04}^h{03}^{m}47.6005s$	${12}^h{27}^{m}08.9729s$	Gaia DR2
Dec. (J2000)	$-44°41\prime 19.6988″$	$-32°45\prime 19.5158″$	$-45°47\prime 57.9955″$	$-19°03\prime 24.3267″$	$-48°58\prime 42.2278″$	Gaia DR2
${\mu }_{R.A.}$ ($\mathrm{mas}{\mathrm{yr}}^{-1}$)	$-3.451\pm 0.054$	$-6.283\pm 0.026$	$-8.604\pm 0.046$	$-12.664\pm 0.046$	$-12.70\pm 0.30$	Gaia DR2
${\mu }_{\mathrm{Dec}.}$ ($\mathrm{mas}{\mathrm{yr}}^{-1}$)	$-7.915\pm 0.093$	$0.531\pm 0.031$	$-2.950\pm 0.035$	$-14.115\pm 0.040$	$-3.23\pm 0.16$	Gaia DR2
Parallax (mas)	$1.308\pm 0.039$	$1.611\pm 0.016$	$1.744\pm 0.035$	$3.550\pm 0.039$	$2.35\pm 0.22$	Gaia DR2
Spectroscopic properties
$T_{\mathrm{eff}\star }$ (K)	$5528\pm 78$	$6095\pm 92$	$6552\pm 61$	$5659\pm 84$	$6460\pm 130$	ZASPEaa Either HATS-54, HATS-55, HATS-56, HATS-57 or HATS-58.
$\left[\mathrm{Fe}/H\right]$	$0.390\pm 0.032$	$0.220\pm 0.049$	$0.200\pm 0.025$	$0.160\pm 0.059$	$0.060\pm 0.069$	ZASPE
$v\sin i$ ($\mathrm{km}{s}^{-1}$)	$3.83\pm 0.42$	$5.01\pm 0.15$	$6.49\pm 0.19$	$4.09\pm 0.48$	$6.22\pm 0.29$	ZASPE
$v_{\mathrm{mac}}$ ($\mathrm{km}{s}^{-1}$)	$3.61\pm 0.11$	$4.48\pm 0.14$	$5.183\pm 0.093$	$3.81\pm 0.13$	$5.04\pm 0.20$	Assumed
$v_{\mathrm{mic}}$ ($\mathrm{km}{s}^{-1}$)	$0.948\pm 0.034$	$1.308\pm 0.079$	$1.832\pm 0.090$	$1.014\pm 0.045$	$1.71\pm 0.17$	Assumed
${\gamma }_{\mathrm{RV}}$ ($m{s}^{-1}$)	$46128\pm 13$	$-2919.9\pm 6.4$	$35148\pm 15$	$544.4\pm 7.6$	$19290.0\pm 8.1$	FEROS/HARPSbb Barycentric Julian Date is computed directly from the UTC time without correction for leap seconds.
${\dot{\gamma }}_{\mathrm{RV}}$ ($m{s}^{-1}$ d-1)	$\cdots$	$\cdots$	$6.469\pm 0.044$	$\cdots$	$\cdots$	FEROS/HARPScc The out-of-transit level has been subtracted. For observations made with the HATSouth instruments (identified by “HS” in the “Instrument” column) these magnitudes have been corrected for trends using the EPD and TFA procedures applied prior to fitting the transit model. This procedure may lead to an artificial dilution in the transit depths. The blend factors for the HATSouth light curves are listed in Table 6. For observations made with follow-up instruments (anything other than “HS” in the “Instrument” column), the magnitudes have been corrected for a quadratic trend in time, and for variations correlated with up to three PSF shape parameters, fit simultaneously with the transit.
${\ddot{\gamma }}_{\mathrm{RV}}$ ($m{s}^{-1}$ d-2)	$\cdots$	$\cdots$	$-0.003400\pm 0.000052$	$\cdots$	$\cdots$	FEROS/HARPScc For HATS-56 the RVs show a significant quadratic trend in addition to the Keplerian orbital variation due to the transiting planet HATS-56b (Fig. 4). This trend is modelled as $\mathrm{RV}\left(t\right)={\gamma }_{\mathrm{RV}}+{\dot{\gamma }}_{\mathrm{RV}}\left(t-T_0\right)+{\ddot{\gamma }}_{\mathrm{RV}}{\left(t-T_0\right)}^2$ where $T_0=2457091.7102\pm 0.0044$ is the center time of the first transit observed in the HATSouth light curve.
Photometric properties
$B$ (mag)	$14.729\pm 0.030$	$14.111\pm 0.020$	$12.097\pm 0.029$	$13.094\pm 0.096$	$12.0510\pm 0.0090$	APASSdd Raw magnitude values without correction for the quadratic trend in time, or for trends correlated with the seeing. These are only reported for the follow-up observations.
$V$ (mag)	$13.913\pm 0.040$	$13.470\pm 0.040$	$11.578\pm 0.023$	$12.344\pm 0.047$	$11.552\pm 0.019$	APASSdd From APASS DR6 for as listed in the UCAC 4 catalog (Zacharias et al., 2012).
$g$ (mag)	$14.301\pm 0.010$	$13.746\pm 0.030$	$11.801\pm 0.022$	$12.669\pm 0.035$	$11.752\pm 0.019$	APASSdd From APASS DR6 for as listed in the UCAC 4 catalog (Zacharias et al., 2012).
$r$ (mag)	$13.681\pm 0.010$	$13.279\pm 0.030$	$11.473\pm 0.017$	$12.129\pm 0.058$	$11.466\pm 0.024$	APASSdd From APASS DR6 for as listed in the UCAC 4 catalog (Zacharias et al., 2012).
$i$ (mag)	$13.52\pm 0.10$	$13.120\pm 0.030$	$11.320\pm 0.046$	$11.949\pm 0.063$	$11.379\pm 0.070$	APASSdd From APASS DR6 for as listed in the UCAC 4 catalog (Zacharias et al., 2012).
$G$ (mag)	$13.77620\pm 0.00040$	$13.34980\pm 0.00030$	$11.48770\pm 0.00080$	$12.18160\pm 0.00070$	$11.7679\pm 0.0015$	Gaia DR2
$BP$ (mag)	$14.1834\pm 0.0024$	$13.6816\pm 0.0010$	$11.7645\pm 0.0016$	$12.5621\pm 0.0027$	$\cdots$	Gaia DR2
$RP$ (mag)	$13.2231\pm 0.0016$	$12.8651\pm 0.0012$	$11.0523\pm 0.0022$	$11.6542\pm 0.0024$	$\cdots$	Gaia DR2
$J$ (mag)	$12.611\pm 0.024$	$12.338\pm 0.026$	$10.514\pm 0.023$	$11.071\pm 0.026$	$10.584\pm 0.024$	2MASS
$H$ (mag)	$12.273\pm 0.025$	$12.048\pm 0.040$	$10.325\pm 0.029$	$10.738\pm 0.023$	$10.358\pm 0.026$	2MASS
$K_s$ (mag)	$12.170\pm 0.019$	$12.020\pm 0.041$	$10.251\pm 0.019$	$10.707\pm 0.027$	$10.289\pm 0.023$	2MASS
Derived properties
$M_{\star }$ ($M_{☉}$)	$1.097\pm 0.022$	${1.1955}_{-0.0119}^{+0.0091}$	$1.573\pm 0.017$	${1.026}_{-0.026}^{+0.019}$	$1.461\pm 0.043$	Joint fit ee Obtained through the joint fit detailed in Hartman et al. (2018) and briefly summarized in Section 3.3.
$R_{\star }$ ($R_{☉}$)	$1.317\pm 0.036$	$1.126\pm 0.011$	$2.201\pm 0.036$	$0.960\pm 0.011$	$1.433\pm 0.059$	Joint fit
$T_{\text{eff}}$ (K)	$5702\pm 26$	$6214\pm 36$	$6536\pm 31$	$5587\pm 19$	$7175\pm 54$	Joint fit
$\log g_{\star }$ (cgs)	$4.240\pm 0.023$	$4.4121\pm 0.0070$	$3.949\pm 0.012$	$4.484\pm 0.016$	$4.292\pm 0.028$	Joint fit
Fe/H (dex)	$0.396\pm 0.031$	${0.108}_{-0.030}^{+0.046}$	$0.190\pm 0.024$	$0.268\pm 0.043$	$\cdots$	Joint fit
${\rho }_{\star }$ ($g{\mathrm{cm}}^{-3}$)	$0.678\pm 0.054$	$1.179\pm 0.029$	$0.2079\pm 0.0090$	$1.633\pm 0.075$	$0.702\pm 0.070$	Joint fit
$L_{\star }$ ($L_{☉}$)	${1.631}_{-0.076}^{+0.114}$	$1.694\pm 0.054$	$7.90\pm 0.31$	$0.805\pm 0.018$	$4.89\pm 0.46$	Joint fit
Age (Gyr)	$6.60\pm 0.76$	${0.40}_{-0.13}^{+0.29}$	$1.894\pm 0.077$	${2.5}_{-1.1}^{+1.5}$	${0.31}_{-0.20}^{+0.33}$	Joint fit
$A_V$ (mag)	$0.279\pm 0.018$	$0.350\pm 0.027$	$0.335\pm 0.017$	$0.055\pm 0.011$	${0.340}_{-0.017}^{+0.024}$	Joint fit
Distance (pc)	$769\pm 21$0	$623.6\pm 6.2$	$577.1\pm 9.6$	$280.0\pm 2.9$	$492\pm 21$	Joint fit

Table 5. Table 6: Orbital and planetary parameters for HATS-54b–HATS-58Ab

	HATS-54b	HATS-55b	HATS-56b	HATS-57b	HATS-58Ab
Parameter	Value	Value	Value	Value	Value
Light curve parameters
$P$ (days)	$2.5441828\pm 0.0000043$	$4.2042001\pm 0.0000033$	$4.324799\pm 0.000027$	$2.3506210\pm 0.0000013$	$4.2180896\pm 0.0000089$
$T_c$ ($\mathrm{BJD}$) aa ZASPE = Zonal Atmospherical Stellar Parameter Estimator routine for the analysis of high-resolution spectra (Brahm et al., 2017b), applied to the FEROS spectra of each system. 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.	$2457780.01102\pm 0.00089$	$2457413.13042\pm 0.00051$	$2457788.0029\pm 0.0012$	$2457778.49589\pm 0.00025$	$2457463.2999\pm 0.0017$
$T_{14}$ (days) aa Times 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. $T_{12}$: 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.	$0.1042\pm 0.0019$	$0.11599\pm 0.00097$	$0.1934\pm 0.0022$	$0.10369\pm 0.00071$	$0.1325\pm 0.0031$
$T_{12}=T_{34}$ (days) aa Times 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. $T_{12}$: 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.	$0.0165\pm 0.0013$	$0.01996\pm 0.00054$	$0.02548\pm 0.00091$	$0.01220\pm 0.00050$	$0.0161\pm 0.0013$
$a/R_{\star }$	$6.15\pm 0.16$	$10.330\pm 0.086$	$5.902\pm 0.085$	$7.82\pm 0.12$	$8.71\pm 0.30$
$\zeta /R_{\star }$ bb The listed ${\gamma }_{\mathrm{RV}}$ is from FEROS for HATS-54, HATS-56, HATS-57 and HATS-58. For HATS-55 it is from HARPS. The error on ${\gamma }_{\mathrm{RV}}$ is determined from the orbital fit to the RV measurements, and does not include the systematic uncertainty in transforming the velocities to the IAU standard system. The velocities have not been corrected for gravitational redshifts.	$22.56\pm 0.50$0	$20.62\pm 0.20$0	$11.85\pm 0.15$0	$21.85\pm 0.13$0	$17.12\pm 0.43$0
$R_p/R_{\star }$	$0.0832\pm 0.0025$	$0.1141\pm 0.0020$	$0.0789\pm 0.0018$	$0.1218\pm 0.0023$	$0.0786\pm 0.0025$
$b^2$	${0.548}_{-0.034}^{+0.032}$	${0.439}_{-0.013}^{+0.015}$	${0.475}_{-0.018}^{+0.019}$	${0.084}_{-0.026}^{+0.033}$	${0.429}_{-0.042}^{+0.041}$
$b\equiv a\cos i/R_{\star }$	${0.740}_{-0.023}^{+0.022}$	${0.662}_{-0.010}^{+0.012}$	${0.690}_{-0.013}^{+0.014}$	${0.290}_{-0.049}^{+0.052}$	${0.655}_{-0.033}^{+0.030}$
$i$ (deg)	$83.08\pm 0.36$0	$86.320\pm 0.084$0	$83.29\pm 0.21$0	$87.88\pm 0.40$0	$85.69\pm 0.33$0
HATSouth dilution factors dd Scaling factor applied to the model transit that is fit to the HATSouth light curves. This factor accounts for dilution of the transit due to blending from neighboring stars and over-filtering of the light curve. These factors are varied in the fit, with independent values adopted for each HATSouth light curve. The factors listed HATS-54, HATS-55, HATS-57 and HATS-58 are for the G700.3, G602.4, G548.3, and G699.1 light curves, respectively. For HATS-56 we list the factors for the G698.1 and G698.4 light curves in order.
Dilution factor 1	$0.937\pm 0.065$	$0.818\pm 0.052$	$0.724\pm 0.064$	$0.795\pm 0.036$	$\cdots$
Dilution factor 2	$\cdots$	$\cdots$	$0.869\pm 0.048$	$\cdots$	$\cdots$
Limb-darkening coefficients ee Values for a quadratic law, adopted from the tabulations by Claret (2004) according to the spectroscopic (ZASPE) parameters listed in Table 5.
$c_1,g$	$0.6588$	$\cdots$	$\cdots$	$\cdots$	$\cdots$
$c_2,g$	$0.1582$	$\cdots$	$\cdots$	$\cdots$	$\cdots$
$c_1,r$	$0.4314$	$0.3112$	$0.2388$	$0.3913$	$0.2489$
$c_2,r$	$0.2867$	$0.3574$	$0.3963$	$0.3070$	$0.3851$
$c_1,R$	$0.4011$	$0.2882$	$0.2170$	$\cdots$	$0.2277$
$c_2,R$	$0.2948$	$0.3585$	$0.3871$	$\cdots$	$0.3845$
$c_1,i$	$0.3222$	$0.2290$	$0.1618$	$0.2951$	$0.1748$
$c_2,i$	$0.3120$	$0.3569$	$0.3903$	$0.3188$	$0.3768$
RV parameters
$K$ ($m{s}^{-1}$)	$105\pm 14$00	$102.8\pm 8.4$00	$55.1\pm 3.2$00	$472.5\pm 8.4$00	$100\pm 22$00
$e$ ff The 95% confidence upper limit on the eccentricity determined when $\sqrt{e}\cos \omega$ and $\sqrt{e}\sin \omega$ are allowed to vary in the fit.
RV jitter FEROS ($m{s}^{-1}$) gg Term added in quadrature to the formal RV uncertainties for each instrument. This is treated as a free parameter in the fitting routine. In cases where the jitter is consistent with zero, we list its 95% confidence upper limit.	$60.5\pm 8.2$	$\cdots$	$21.8\pm 3.2$	$24.1\pm 6.1$	$51\pm 13$
RV jitter HARPS ($m{s}^{-1}$)				$\cdots$
Planetary parameters
$M_p$ ($M_J$)	$0.76\pm 0.10$	$0.921\pm 0.076$	$0.602\pm 0.035$	$3.147\pm 0.073$	$1.03\pm 0.23$
$R_p$ ($R_J$)	$1.067\pm 0.052$	$1.251\pm 0.026$	${1.688}_{-0.055}^{+0.039}$	$1.139\pm 0.028$	$1.095\pm 0.062$
$C(M_p,R_p)$ hh Correlation coefficient between the planetary mass $M_p$ and radius $R_p$ estimated from the posterior parameter distribution.	$-0.11$	$-0.07$	$0.06$	$-0.12$	$\cdots$
${\rho }_p$ ($g{\mathrm{cm}}^{-3}$)	$0.77\pm 0.16$	$0.587\pm 0.062$	${0.155}_{-0.013}^{+0.017}$	$2.65\pm 0.21$	$0.96\pm 0.27$
$\log g_p$ (cgs)	$3.216\pm 0.076$	$3.165\pm 0.042$	$2.718\pm 0.034$	$3.779\pm 0.025$	$3.33\pm 0.11$
$a$ (AU)	$0.03763\pm 0.00024$	${0.05412}_{-0.00018}^{+0.00014}$	$0.06043\pm 0.00022$	${0.03493}_{-0.00030}^{+0.00021}$	$0.05798\pm 0.00057$
$T_{\mathrm{eq}}$ (K)	$1625\pm 22$	$1367\pm 10$	$1902\pm 16$	$1413.4\pm 9.7$	$1721\pm 34$
$\Theta$ ii The Safronov number is given by $\Theta =\frac{1}{2}{\left(V_{\mathrm{esc}}/V_{\mathrm{orb}}\right)}^2=\left(a/R_p\right)\left(M_p/M_{\star }\right)$ (see Hansen & Barman, 2007).	$0.0482\pm 0.0071$	$0.0666\pm 0.0057$	$0.0271\pm 0.0018$	$0.1875\pm 0.0055$	$0.074\pm 0.017$
${\log }_{10}⟨F⟩$ (cgs) jj Incoming flux per unit surface area, averaged over the orbit.	$9.197\pm 0.023$	$8.896\pm 0.013$	$9.469\pm 0.014$	$8.954\pm 0.012$	$9.296\pm 0.034$

Equations

$$k(\tau )=\frac{B}{2+C}{e}^{-\tau /L}\left[\cos \left(\frac{2\pi \tau }{P_{\text{GP}}}\right)+(1+C)\right],$$

Full text

planetary systems — stars: individual (

HATS-54, GSC 7799-01184, HATS-55, GSC 7109-00596 HATS-56, GSC 8229-02228 HATS-57, GSC 5885-00663 HATS-58A, GSC 8239-00065 ) techniques: spectroscopic, photometric

1 Introduction

With almost 3,000 confirmed exoplanets111http://www.exoplanets.org/, the field of exoplanet discovery and characterization has seen an exponential increase in the number of discovered far-away worlds. While space-based dedicated surveys such as Kepler (Borucki et al., 2010) have excelled at the detection of small ($R_{p}<4R_{\earth}$) exoplanets, ground-based dedicated surveys such as HATNet (Bakos et al., 2004), HATSouth (Bakos et al., 2013a), WASP (Pollacco et al., 2006), KELT (Pepper et al., 2018) and the recently started MASCARA (Snellen et al., 2012) and NGTS (Wheatley et al., 2018) surveys have been pioneering the search of giant exoplanets. This has produced a sample of exoplanets amenable for characterization both in terms of radial-velocity follow-up — which allows us to constrain their densities — or in terms of atmospheric follow-up — which allows us to have a glimpse at what their atmospheres look like. It has also generated a large sample of well-characterized exoplanets from which we have been able to extract useful information to put our planet formation and evolution theories to test.

Despite the relatively large number of known exoplanets, less than $10\%$ ($\sim 300$) are well-characterized (i.e., have a mass and radius constrained to better than 20% precision). Discovered mostly from ground-based transit surveys, these — mostly short-period ($P\lesssim 10$ days), hot — transiting giant exoplanets have provided unique information that has aided in the understanding of the formation, evolution and composition of those far-away worlds. For example, structure modelling coupled with the mass, radius and ages of the warmer (¡ 1000 K) of these systems has allowed us to understand that they are heavily enriched in metals (Thorngren et al., 2016), which in turn has explicit predictions for their compositions (Espinoza et al., 2017). This understanding, in turn, has allowed us to calibrate how mass and heavy elements are related, which in turn has been used to elucidate the nature of the observed radius inflation of highly irradiated giant exoplanets, bringing us closer to an understanding of the mechanism(s) producing this radius anomaly over a wide range of stellar irradiation, masses and sizes (Thorngren & Fortney, 2018a; Sestovic et al., 2018). In terms of formation, short-period giant exoplanets are fundamental probes of the mechanisms that shape their orbits to their present-day forms. Although in-situ formation has still not been ruled out (Batygin et al., 2016), the orbital migration scenario — either by direct disk migration and/or by interaction with other bodies in the system (see, e.g., Lin et al., 1996; Li et al., 2014; Petrovich, 2015) — is by far the most popular theory to explain the observed short-period orbits of these hot giant exoplanets. All of them have discerning features that can be studied with transiting exoplanets, for which one is able to unveil their 3-dimensional orbital shapes if sufficient follow-up is performed. In addition, some transiting systems actually reside in systems with other planetary or sub-stellar companions (see, e.g., Becker et al., 2015; Rey et al., 2018; Sarkis et al., 2018; Yee et al., 2018), which provides new laboratories to study how multiplanetary systems form and evolve.

In this work we present the discovery of five new transiting hot giant exoplanets, one of which is in a possible multiplanetary system with a sub-stellar companion on a possible temperate, eccentric orbit. The paper is divided as follows. Section 2 details our observations, including the HATSouth photometric detection and both photometric and radial-velocity follow-up. Section 3 details the analysis of the data presented, while in Section 4 we discuss our results. Finally, in Section 5 we present our conclusions.

2 Observations

2.1 Photometric detection

The photometric detection of the exoplanets presented in this work was made with the HATSouth units based in Las Campanas Observatory (LCO; HS-1 and HS-2), at the HESS site in Namibia (HS-3 and HS-4) and at the site in Siding Spring Observatory (SSO; HS-5 and HS-6), whose operations are described in detail in Bakos et al. (2013b). The details of these observations for each of the presented exoplanets can be found in Table 1.

As with previous results from our group, the data was reduced and analyzed with the procedures detailed in Bakos et al. (2013b) and Penev et al. (2013); briefly, the lightcurves were detrended using the trend-filtering algorithm (Kovács et al., 2005) as described in Bakos et al. (2013b), and then a search for periodic, transit-like signals using the Box-fitting Least-Squares algorithm (BLS; see Kovács et al., 2002) was performed. Peaks in the BLS periodogram were found for HATS-54, HATS-55, HATS-56, HATS-57 and HATS-58 with periods of 2.54, 4.20, 4.32, 2.35 and 4.21 days, respectively, which prompted us to obtain further photometric and spectroscopic follow-up in order to confirm the planetary nature of the signals, which we detail in the following sections. The phase-folded lightcurves for each planet are presented in Figures 1 and 2. The data are presented in Table 1.

The lightcurves were also further analyzed in the search for additional periodic signals, either transit-like (with BLS, in the search for additional transiting companions in the system) or sinusoidal (with the Generalized Lomb-Scargle — GLS — periodogram described by Zechmeister & Kürster, 2009, in the search for signals of non-transiting companions and/or intrinsic variability of the star). For this, the portions of the detected transits were masked out, and GLS and BLS periodograms were produced and inspected. No additional signals were found using GLS and BLS in our lightcurves for HATS-54, HATS-55, HATS-56 and HATS-58. However, the lightcurve of HATS-57 shows two clear peaks in the GLS periodogram at 6 and 12.8-days. A visual inspection to the lightcurve shows that the star is clearly undergoing quasi-periodic modulations with signatures typical to that of starspots going in and out of view, with a peak-to-peak variation of $\sim 2$%. We analyze this signature in detail in Section 3.1.

\startlongtable

2.2 Spectroscopic Observations

Spectroscopic follow-up was performed on our planet candidates in order to confirm their planetary nature. This spectroscopic follow-up, as in previous works, was divided in two types: (1) reconnaissance spectroscopy, usually performed with lower-resolution instruments and which serves in order to both get coarse stellar atmospheric parameters (to identify, e.g., if the target is a giant star by the derived value of its log-gravity) and identify if there is any large radial-velocity variation (indicative of an eclipsing binary and/or blend), and (2) high-precision spectroscopy, used to both obtain better stellar atmospheric parameters and to measure the radial-velocity signature that our candidate planets should imprint on the star.

Reconnaissance spectroscopy was performed with the Wide Field Spectrograph (WiFeS Dopita et al., 2007), located on the Australian National University (ANU) 2.3m telescope and the CORALIE (Queloz et al., 2001) spectrograph, mounted on the 1.2m Euler Telescope at La Silla Observatory (LSO). The observing strategy, reduction and data processing of the WiFeS spectra can be found in Bayliss et al. (2013), whereas the CORALIE data were reduced using the CERES pipeline (Brahm et al., 2017a). WiFeS spectra were obtained for HATS-54 (4 spectra), HATS-55 (4 spectra), HATS-57 (3 spectra) and HATS-58 (3 spectra), all of which passed our initial screenings in terms of having high surface gravities ($\log g\geq 4$) and no large radial-velocity variations ($\leq 1$ km s*-1*). HATS-55 (4 spectra), HATS-56 (1 spectra) and HATS-58 (1 spectra) had CORALIE spectra taken, which also helped to rule out false positives with similar standards as for the WiFeS data.

High-precision spectroscopy, on the other hand, was performed with both the FEROS (Kaufer & Pasquini, 1998) and HARPS (Mayor et al., 2003) spectrographs, which are located at the MPG 2.2m telescope and 3.6m ESO telescope, respectively, at LSO. Data obtained from both of those instruments was also reduced with the CERES pipeline. Details of all the spectroscopic observations are provided in Table 2. The observed high-precision radial velocities are presented in Table 2.2.

All of our targets showed radial-velocity variations at the periods of the observed transits consistent with being of planetary nature, with no indication of being correlated with other stellar parameters (e.g., bisector spans). HATS-56, however, showed an additional long-term trend radial-velocity signal, which shows no correlation with other parameters (e.g., bisector span). The phase-folded radial-velocities are presented in Figures 3 and 4. We analyze these in detail in Section 3.3.

\startlongtable