Astronomy & Astrophysics manuscript no. dnaef˙7361˙final c© ESO 2021
August 29, 2021
The HARPS search for southern extra-solar planets.
IX. Exoplanets orbiting HD 100777, HD 190647, and HD 221287?
D. Naef1,2, M. Mayor2, W. Benz3, F. Bouchy4, G. Lo Curto1, C. Lovis2, C. Moutou5, F. Pepe2, D. Queloz2,
N.C. Santos2,6,7, and S. Udry2
1 European Southern Observatory, Casilla 19001, Santiago 19, Chile
2 Observatoire Astronomique de l’Université de Genève, 51 Ch. des Maillettes, CH-1290 Sauverny, Switzerland
3 Physikalisches Institut Universität Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
4 Institut d’Astrophysique de Paris, UMR7095, Université Pierre & Marie Curie, 98 bis Bd Arago, F-75014 Paris, France
5 Laboratoire d’Astrophysique de Marseille, Traverse du Siphon, F-13376 Marseille 12, France
6 Centro de Astronomia e Astrofı́sica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, P-1349-018
Lisboa, Portugal
7 Centro de Geofı́sica de Évora, Rua Romão Ramalho 59, P-7002-554 Évora, Portugal
Received 27 February 2007 / Accepted 11 April 2007
ABSTRACT
Context. The HARPS high-resolution high-accuracy spectrograph was made available to the astronomical community in the second
half of 2003. Since then, we have been using this instrument for monitoring radial velocities of a large sample of Solar-type stars
(' 1400 stars) in order to search for their possible low-mass companions.
Aims. Amongst the goals of our survey, one is to significantly increase the number of detected extra-solar planets in a volume-limited
sample to improve our knowledge of their orbital elements distributions and thus obtain better constraints for planet-formation models.
Methods. Radial-velocities were obtained from high-resolution HARPS spectra via the cross-correlation method. We then searched
for Keplerian signals in the obtained radial-velocity data sets. Finally, companions orbiting our sample stars were characterised using
the fitted orbital parameters.
Results. In this paper, we present the HARPS radial-velocity data and orbital solutions for 3 Solar-type stars: HD 100777, HD 190647,
and HD 221287. The radial-velocity data of HD 100777 is best explained by the presence of a 1.16 MJup planetary companion on a
384–day eccentric orbit (e = 0.36). The orbital fit obtained for the slightly evolved star HD 190647 reveals the presence of a long-
period (P = 1038 d) 1.9 MJup planetary companion on a moderately eccentric orbit (e = 0.18). HD 221287 is hosting a 3.1 MJup planet
on a 456–day orbit. The shape of this orbit is not very well-constrained because of our non-optimal temporal coverage and because of
the presence of abnormally large residuals. We find clues that these large residuals result from spectral line-profile variations probably
induced by processes related to stellar activity.
Key words. stars: individual: HD 100777 – stars: individual: HD 190647 – stars: individual: HD 221287 – stars: planetary systems –
techniques: radial velocities
1. Introduction
The High Accuracy Radial-velocity Planet Searcher (HARPS,
Pepe et al. 2002, 2004; Mayor et al. 2003) was put in opera-
tion during the second half of 2003. HARPS is a high-resolution,
fiber-fed echelle spectrograph mounted on the 3.6–m telescope
at ESO–La Silla Observatory (Chile). It is placed in a vacuum
vessel and is accurately thermally-controlled (temperature varia-
tions are less than 1 mK over one night, less than 2 mK over one
month). Its most striking characteristic is its unequaled stability
and radial-velocity (RV) accuracy: 1 m s−1 in routine operations.
A sub-m s−1 accuracy can even be achieved for inactive, slowly
rotating stars when an optimized observing strategy aimed at
averaging out the stellar oscillations signal is applied (Santos
et al. 2004a; Lovis et al. 2006).
Send offprint requests to: D. Naef e-mail: dnaef@eso.org
? Based on observations made with the HARPS instrument on the
ESO 3.6-m telescope at the La Silla Observatory (Chile) under the GTO
programme ID 072.C-0488.
The HARPS Consortium that manufactured the instrument
for ESO has received Guaranteed Time Observations (GTO). The
core programme of the HARPS-GTO is a very high RV-precision
search for low-mass planets around non-active and slowly ro-
tating Solar-type stars. Another programme carried out by the
HARPS-GTO is a lower RV precision planet search. It is a survey
of about 850 Solar-type stars at a precision better than 3 m s−1.
The sample is a volume-limited complement (up to 57.5 pc) of
the CORALIE sample (Udry et al. 2000). The goal of this sub-
programme is to obtain improved Jupiter-sized planets orbital
elements distributions by substantially increasing the size of the
exoplanets sample. Statistically robust orbital elements distribu-
tions put strong constraints on the various planet formation sce-
narios. The total number of extra-solar planets known so far is
over 200. Nevertheless, some sub-categories of planets with spe-
cial characteristics (e.g. hot-Jupiters or very long-period planets)
are still weakly populated. The need for additional detections
thus remains high.
With typical measurement precisions of 2-3 m s−1, the
HARPS volume-limited programme does not necessarily aim at
2 D. Naef et al.: The HARPS search for southern extra-solar planets IX
Table 1. Observed and inferred stellar characteristics of
HD 100777, HD 190647, and HD 221287 (see text for details).
HD 100777 HD 190647 HD 221287
HIP 56572 99115 116084
Type K0 G5 F7V
mV 8.42 7.78 7.82
B − V 0.760 0.743 0.513
π [mas] 18.84± 1.14 18.44± 1.10 18.91± 0.82
d [pc] 52.8+3.4
−3.0 54.2
−3.1 52.9
MV 4.807 4.109 4.203
B.C. −0.119 −0.109 −0.010
L [L�] 1.05 1.98 1.66
Teff [K] 5582± 24 5628± 20 6304± 45
log g [cgs] 4.39± 0.07 4.18± 0.05 4.43± 0.16
[Fe/H] 0.27± 0.03 0.24± 0.03 0.03± 0.05
Vt [km s−1] 0.98± 0.03 1.06± 0.02 1.27± 0.12
M∗ [M�] 1.0± 0.1 1.1± 0.1 1.25± 0.10
log R
HK −5.03 −5.09 −4.59
Prot [d] 39± 2 39± 2 5.0± 2
age [Gyr] >2 >2 1.3
v sin i [km s−1] 1.8± 1.0 2.4± 1.0 4.1± 1.0
detecting very low-mass planetary companions, and it is mostly
sensitive to planets that are more massive than Saturn. To date,
it has already allowed the detection of several short-period pla-
nets: HD 330075 b (Pepe et al. 2004), HD 2638 b, HD 27894 b,
HD 63454 b (Moutou et al. 2005), and HD 212301 b (Lo Curto
et al. 2006).
In this paper, we report the detection of 3 longer-period pla-
netary companions orbiting stars in the volume-limited sample:
HD 100777 b, HD 190647 b, and HD 221287 b. In Sect. 2, we de-
scribe the characteristics of the 3 host stars. In Sect. 3, we present
our HARPS radial-velocity data and the orbital solutions for the
3 targets. In Sect. 3.4, we discuss the origin of the high residuals
to the orbital solution for HD 221287. Finally, we summarize our
findings in Sect. 4.
2. Stellar characteristics of HD 100777, HD 190647,
and HD 221287
The main characteristics of HD 100777, HD 190647, and
HD 221287 are listed in Table 1. Spectral types, apparent magni-
tudes mV, colour indexes B − V , astrometric parallaxes π, and
distances d are from the HIPPARCOS Catalogue (ESA 1997).
From the same source, we have also retrieved information on
the scatter in the photometric measurements and on the good-
ness of the astrometric fits for the 3 targets. The photometric
scatters are low in all cases. HD 190647 is flagged as a constant
star. The goodness-of-fit parameters are close to 0 for the 3 stars,
indicating that their astrometric data are explained by a single-
star model well. Finally, no close-in faint visual companions are
reported around these objects in the HIPPARCOS Catalogue.
We performed LTE spectroscopic analyses of high signal-
to-noise ratio (SNR) HARPS spectra for the 3 targets follow-
ing the method described in Santos et al. (2004b). Effective
temperatures (Teff), gravities (log g), iron abundances ([Fe/H]),
and microturbulence velocities (Vt) indicated in Table 1 re-
sult from these analyses. Like most of the planet-hosting stars
Table 2. HARPS radial-velocity data obtained for HD 100777.
Julian date RV Uncertainty
BJD− 2 400 000 [d] [km s−1]
53 063.7383 1.2019 0.0016
53 377.8740 1.2380 0.0015
53 404.7626 1.2205 0.0014
53 407.7461 1.2164 0.0014
53 408.7419 1.2176 0.0016
53 409.7891 1.2161 0.0015
53 468.6026 1.2109 0.0016
53 470.6603 1.2122 0.0021
53 484.6703 1.2273 0.0013
53 489.5948 1.2319 0.0022
53 512.5671 1.2494 0.0017
53 516.5839 1.2539 0.0014
53 518.5962 1.2554 0.0021
53 520.5778 1.2558 0.0022
53 543.5598 1.2649 0.0013
53 550.5289 1.2641 0.0016
53 573.4689 1.2682 0.0014
53 579.4705 1.2641 0.0022
53 724.8617 1.2520 0.0012
53 762.8169 1.2355 0.0013
53 765.7645 1.2311 0.0016
53 781.8894 1.2242 0.0016
53 789.7730 1.2209 0.0018
53 862.6200 1.2217 0.0015
53 866.6037 1.2239 0.0014
53 871.6270 1.2357 0.0015
53 883.5589 1.2397 0.0014
53 918.4979 1.2589 0.0017
53 920.5110 1.2613 0.0023
(Santos et al. 2004b), HD 100777 and HD 190647 have very high
iron abundances, more than 1.5 times the solar value, whereas
HD 221287 has a nearly solar metal content. Using the spec-
troscopic effective temperatures and the calibration in Flower
(1996), we computed bolometric corrections. Luminosities were
obtained from the bolometric corrections and the absolute ma-
gnitudes. The low gravity and the high luminosity of HD 190647
indicate that this star is slightly evolved. The other two stars
are still on the main sequence. Stellar masses M∗ were derived
from L, Teff , and [Fe/H] using Geneva and Padova evolutiona-
ry models (Schaller et al. 1992; Schaerer et al. 1993; Girardi
et al. 2000). Values of the projected rotational velocities, v sin i,
were derived from the widths of the HARPS cross-correlation
functions using a calibration obtained following the method de-
scribed in Santos et al. (2002, see their Appendix A) 1
Stellar activity indexes log R
HK (see the index definition
in Noyes et al. 1984) were derived from Ca II K line core re-
emission measurements on high-SNR HARPS spectra following
the method described in Santos et al. (2000). Using these va-
lues and the calibration in Noyes et al. (1984), we derived es-
timates of the rotational periods and stellar ages. The chromo-
spheric ages obtained with this calibration for HD 100777 and
HD 190647 are 6.2 and 7.6 Gyr. Pace & Pasquini (2004) have
shown that chromospheric ages derived for very low-activity,
Solar-type stars were not reliable. This is due to the fact that
the chromospheric emission drops rapidly after 1 Gyr and be-
comes virtually constant after 2 Gyr. For this reason, we have
chosen to indicate ages greater than 2 Gyr instead of the cali-
1 Using cross-correlation function widths for deriving projected rota-
tional velocities is a method that was first proposed by Benz & Mayor
(1981).
D. Naef et al.: The HARPS search for southern extra-solar planets IX 3
Fig. 1. Top: HARPS radial-velocity data (dots) for HD 100777
and fitted orbital solution (solid curve). The radial-velocity sig-
nal is induced by the presence of a 1.16 MJup planetary compan-
ion on a 384-day orbit. Bottom: Residuals to the fitted orbit. The
scatter of these residuals is compatible with the velocity uncer-
tainties.
brated values for these two stars. HD 221287 is much more active
and thus younger making its chromospheric age estimate more
reliable: 1.3 Gyr. We have also measured the lithium abundance
for this target following the method described in Israelian et al.
(2004) and again using a high-SNR HARPS spectrum. The mea-
sured equivalent width for the Li I λ6707.70Å line (deblended
from the Fe I λ6707.44Å line) is 66.6 mÅ leading to the fol-
lowing lithium abundance: log n(Li) = 2.98. Unfortunately, the
lithium abundance cannot provide any reliable age constraint in
our case. Studies of the lithium abundances of open cluster main
sequence stars have shown that log n(Li) remains constant and
equals ' 3 for Teff = 6300 K stars older than a few million years
(see for example Sestito & Randich 2005).
From the activity level reported for HD 221287
(log R
HK =−4.59), we can estimate the expected level of
activity-induced radial-velocity scatter (i.e. the jitter). Using
the results obtained by Santos et al. (2000) for stars with
similar activity levels and spectral types, the range of expected
jitter is between 8 and 20 m s−1. A similar study made on a
different stellar sample by Wright (2005) gives similar results:
an expected jitter of the order of 20 m s−1 (from the fit this
author presents in his Fig. 4). It has to be noted that both
studies contain very few F stars and even fewer high-activity
F stars. This results from the stellar sample they have used:
planet search samples selected against rapidly-rotating young
stars. Their predictions for the expected jitter level are therefore
not well-constrained for active F stars. Both HD 100777 and
HD 190647 are inactive and slowly rotating. Following the same
studies, low jitter values are expected in both cases: ≤ 8 m s−1.
Table 3. HARPS radial-velocity data obtained for HD 190647.
Julian date RV Uncertainty
BJD− 2 400 000 [d] [km s−1]
52 852.6233 −40.2874 0.0013
52 854.6727 −40.2868 0.0013
53 273.5925 −40.2435 0.0022
53 274.6041 −40.2354 0.0024
53 468.8874 −40.2688 0.0015
53 470.8634 −40.2689 0.0014
53 493.9234 −40.2700 0.0029
53 511.9022 −40.2723 0.0015
53 543.8020 −40.2785 0.0013
53 550.7721 −40.2804 0.0014
53 572.8074 −40.2818 0.0015
53 575.7266 −40.2844 0.0017
53 694.5136 −40.3056 0.0014
53 836.9226 −40.2982 0.0015
53 861.8630 −40.2950 0.0017
53 883.8224 −40.2907 0.0013
53 886.8881 −40.2883 0.0013
53 917.8390 −40.2785 0.0021
53 921.8472 −40.2785 0.0018
53 976.6039 −40.2623 0.0014
53 979.6654 −40.2610 0.0017
3. HARPS radial-velocity data
Stars belonging to the volume-limited HARPS-GTO sub-
programme are observed most of the time without the simulta-
neous Thorium-Argon reference (Baranne et al. 1996). The ob-
tained radial velocities are thus uncorrected for possible instru-
mental drifts. This only has a very low impact on our results
as the HARPS radial-velocity drift is less than 1 m s−1 over one
night. For this large volume-limited sample, we aim at a radial-
velocity precision of the order of 3 m s−1 (or better). This corres-
ponds roughly to an SNR of 40-50 at 5500Å. For bright targets
like the three stars of this paper, the exposure times required for
reaching this signal level can be very short as an SNR of 100
(at 5500Å) is obtained with HARPS in a 1-minute exposure on
a 6.5 mag G dwarf under normal weather and seeing conditions.
In order to limit the impact of observing overheads (telescope
preset, target acquisition, detector read-out), we normally do not
use exposure times less than 60 seconds. As a consequence, the
SNR obtained for bright stars is significantly higher than the tar-
geted one, and the output measurement errors are frequently be-
low 2 m s−1.
For our radial-velocity measurements, we consider two main
error terms. The first one is obtained through the HARPS Data
Reduction Software (DRS). It includes all the known calibration
errors (' 20 cm s−1), the stellar photon-noise, and the error on
the instrument drift. For observations taken with the simultane-
ous reference, the drift error is derived from the photon noise
of the Thorium-Argon exposure. For observations taken without
the lamp, a drift error term of 50 cm s−1 is quadratically added.
The second main error term is called the non-photonic error. It
includes guiding errors and a lower limit for the stellar pulsa-
tion signals. For the volume-limited programme, we use an ad-
hoc value for this term: 1.0 m s−1. Stellar noise (activity jitter,
pulsation signal) can of course be greater in some cases (as for
example for HD 221287, cf. Sect. 3.3). The non-photonic term
nearly vanishes for targets belonging to the very high RV pre-
cision sample (non-active stars, pulsation modes averaged out
by the specific observing strategy). In this latter case, this term
thus only contains the guiding errors: ' 30 cm s−1. The error bars
4 D. Naef et al.: The HARPS search for southern extra-solar planets IX
Fig. 2. Top: HARPS radial-velocity data (dots) for HD 190647
and fitted orbital solution (solid curve). The radial-velocity sig-
nal is induced by the presence of a 1.9 MJup planetary companion
on a 1038-day orbit. Bottom: Residuals to the fitted orbit. The
scatter of these residuals is compatible with the velocity uncer-
tainties.
listed in this paper correspond to the quadratic sum of the DRS
and the non-photonic errors.
In the following sections, we present the HARPS radial-
velocity data obtained for HD 100777, HD 190647, and
HD 221287 in more detail, as well as the orbital solutions fitted
to the data.
3.1. A 1.16 MJup planet around HD 100777
We have gathered 29 HARPS radial-velocity measurements of
HD 100777. These data span 858 days between February 27th
2004 (BJD = 2 453 063) and July 4th 2006 (BJD = 2 453 921).
Their mean radial-velocity uncertainty is 1.6 m s−1 (mean DRS
error: 1.3 m s−1). We list these measurements in Table 2 (elec-
tronic version only).
A nearly yearly signal is present in these data. We fit-
ted a Keplerian orbit. The resulting parameters are listed in
Table 5. The fitted orbit is displayed in Fig. 1, together with our
radial-velocity measurements. The radial-velocity data is best
explained by the presence of a 1.16 MJup planet on a 384 d fairly
eccentric orbit (e = 0.36). The inferred separation between the
host star and its planet is a = 1.03 AU. Both m2 sin i and a were
computed using a primary mass of 1 M�.
We performed Monte-Carlo simulations using the ORBIT
software (see Sect. 3.1. in Forveille et al. 1999) in order to
double-check the parameter uncertainties. The errorbars ob-
tained from these simulations are quasi-symmetric and some-
what larger ('18%) than the ones obtained from the covariance
matrix of the Keplerian fit. The errors we have finally quoted in
Table 5 are the Monte-Carlo ones. The residuals to the fitted orbit
(see bottom panel of Fig. 1) are flat and have a dispersion com-
patible with the measurement noise. The low reduced χ2 value
(1.45) and the χ2 probability (0.074) further demonstrate the
Table 4. HARPS radial-velocity data obtained for HD 221287.
Julian date RV Uncertainty
BJD− 2 400 000 [d] [km s−1]
52 851.8534 −21.9101 0.0012
52 853.8544 −21.9201 0.0021
52 858.7810 −21.9252 0.0019
53 264.7097 −21.8617 0.0021
53 266.6805 −21.8852 0.0020
53 268.7030 −21.8595 0.0034
53 273.6951 −21.8888 0.0031
53 274.7129 −21.8718 0.0021
53 292.6284 −21.9049 0.0020
53 294.6239 −21.8998 0.0019
53 295.6781 −21.9017 0.0024
53 296.6388 −21.9186 0.0026
53 339.6009 −21.9289 0.0015
53 340.5974 −21.9225 0.0013
53 342.5955 −21.9172 0.0013
53 344.5961 −21.9428 0.0014
53 345.5923 −21.9291 0.0013
53 346.5566 −21.9284 0.0013
53 546.9385 −21.8022 0.0039
53 550.9121 −21.8294 0.0022
53 551.9479 −21.7956 0.0018
53 723.5707 −21.8679 0.0033
53 727.5302 −21.8815 0.0021
53 862.9297 −21.9205 0.0023
53 974.7327 −21.8240 0.0021
53 980.7273 −21.8192 0.0022
good fit quality. The presence of another massive short-period
companion around HD 100777 is thus unlikely.
3.2. A 1.9 MJup planet orbiting HD 190647
Between August 1, 2003 (BJD = 2 452 852) and September 2,
2006 (BJD = 2 453 980), we obtained 21 HARPS radial-velocity
measurements for HD 190647. These data have a mean radial-
velocity uncertainty of 1.7 m s−1 (mean DRS error: 1.3 m s−1).
We list these measurements in Table 3 (electronic version only).
A long-period signal is clearly present in the RV data. We
performed a Keplerian fit. The resulting fitted parameters are
listed in Table 5. The fitted orbital period (1038 d) is slightly
shorter than the observing time span (1128 d) and the orbital
eccentricity is low (0.18). Monte-Carlo simulations were car-
ried out. The uncertainties on the orbital parameters obtained in
this case are nearly symmetric and a bit larger ('18%) than the
ones resulting from the Keplerian fit. In Table 5, we have listed
these more conservative Monte-Carlo uncertainties. The small
discrepancy between the two sets of errorbars is most probably
due to the rather short time span of the observations (only 1.09
orbital cycle covered) and to our still not optimal coverage of
both the minimum and the maximum of the radial-velocity orbit.
From the fitted parameters and with a primary mass of 1.1 M�,
we compute a minimum mass of 1.90 MJup for this planetary
companion. The computed separation between the two bodies
is 2.07 AU. Figure 2 shows our data and the fitted orbit.
The weighted rms of the residuals (1.6 m s−1) is slightly
smaller than the mean RV uncertainty. The low dispersion of the
residuals, the low reduced χ2 value, and its associated proba-
bility (0.11) allow us to exclude the presence of an additional
massive short-period companion.
D. Naef et al.: The HARPS search for southern extra-solar planets IX 5
Fig. 3. Top: HARPS radial-velocity data (dots) for HD 221287
and fitted orbital solution (solid curve). The detected Keplerian
signal is induced by a 3.1 MJup planet on a 456–day orbit.
Because of a non-optimal coverage of the radial-velocity maxi-
mum and the presence of stellar activity-induced jitter, the ex-
act shape of the orbit is not very well-constrained. Bottom:
Residuals to the fitted orbit. The scatter of these residuals is
much larger than the velocity uncertainties. This large dispersion
is probably due to the fairly high activity level of this star.
3.3. A 3.1 MJup planetary companion to HD 221287
A total of 26 HARPS radial-velocity data were obtained
for HD 221287. These data are spread over 1130 days: be-
tween July 31, 2003 (BJD = 2 452 851) and September 3, 2006
(BJD = 2 453 981). Unlike the two other targets presented in
this paper, a substantial fraction ('65%) of these velocities
were taken using the simultaneous Thorium-Argon reference.
They were thus corrected for the measured instrumental velocity
drifts. The mean radial-velocity uncertainty computed for this
data set is 2.1 m s−1 (mean DRS error: 1.8 m s−1). We list these
measurements in Table 4 (electronic version only).
A 456 d radial-velocity variation is clearly visible in our data
(see Fig. 3). This period is two orders of magnitude longer than
the rotation period obtained from the Noyes et al. (1984) cali-
bration for HD 221287: 5± 2 d. This large discrepancy between
PRV and Prot is probably sufficient for safely excluding stellar
spots as the origin of the detected RV signal, but we nevertheless
checked if this variability could be due to line-profile variations.
The cross-correlation function (CCF) bisector span versus radial
velocity plot is shown in the top panel of Fig. 4. The average
CCF bisector value is computed in two selected regions: near the
top of the CCF (i.e. near the continuum) and near its bottom (i.e
near the RV minimum). The span is the difference between these
two average values (top−bottom) and thus represents the overall
slope of the CCF bisector (for details, see Queloz et al. 2001).
As for the case of HD 166435 presented in Queloz et al.
(2001), an anti-correlation between spans and velocities is
expected in the case of star-spot induced line-profile varia-
tions. The bisector span data are quite noisy (weighted rms of
10.4 m s−1), but they are not correlated with the RV data. The
Fig. 4. a: Bisector span versus radial-velocity plot for
HD 221287. The dispersion of the span data is quite
large (10.4 m s−1) revealing potential line-profile variations.
Nevertheless, the main radial-velocity signal is not correlated
to these profile variations and is thus certainly of Keplerian
origin. b: Bisector span versus radial-velocity residuals to the
Keplerian orbit (see Table 5) displayed in the same velocity
scale. A marginal anti-correlation between the two quantities is
observed.
main signal can therefore not be due to line-profile variations
and certainly has a Keplerian origin.
Table 5 contains the results of a Keplerian fit that we per-
formed. Our data and the fitted orbit are displayed in Fig. 3. The
RV maximum remains poorly covered by our observations. As
for the other two targets, we made Monte-Carlo simulations for
checking our orbital parameter uncertainties. As expected, the
uncertainties obtained in this case largely differ from the ones
obtained via the Keplerian fit. For most of the parameters, the
errorbars resulting from the simulations are not symmetric and
much larger ('5 times larger). In order to be more conserva-
tive, we have chosen to quote these errors in Table 5. The shape
of the orbit is not very well-constrained, but there is no doubt
about the planetary nature of HD 221287 b. The fitted eccen-
tricity is low (0.08), but circular or moderately eccentric orbits
(up to 0.25) cannot be excluded yet. Using a primary mass of
1.25 M�, we compute the companion minimum mass and sepa-
ration: m2 sin i = 3.09 MJup and a = 1.25 AU.
6 D. Naef et al.: The HARPS search for southern extra-solar planets IX
Table 5. HARPS orbital solutions for HD 100777, HD 190647, and HD 221287.
HD 100777 HD 190647 HD 221287
P [d] 383.7± 1.2 1038.1± 4.9 456.1± +7.7
T [JD†] 456.2± 2.3 868± 24 263± +99
e 0.36± 0.02 0.18± 0.02 0.08± +0.17
−0.05
γ [km s−1] 1.246± 0.001 −40.267± 0.001 −21.858± +0.008
−0.005
ω [◦] 202.7± 3.1 232.5± 9.4 98± +92
K1 [m s−1] 34.9± 0.8 36.4± 1.2 71± +18−8
f (m) [10−9M�] 1.37± 0.10 4.94± 0.50 16.4± 12.6
a1 sin i [10−3AU] 1.15± 0.03 3.42± 0.12 2.95± 0.75
m2 sin i [MJup] 1.16± 0.03 1.90± 0.06 3.09± 0.79
a [AU] 1.03± 0.03 2.07± 0.06 1.25± 0.04
N 29 21 26
\ [m s−1] 1.7 1.6 8.5
χ2red
? 1.45 1.46 26.7
p(χ2, ν)‡ 0.074 0.11 0
† JD = BJD− 2 453 000
\ σO−C is the weighted rms of the residuals (weighted by 1/�2, where � is the O−C uncertainty)
? χ2red = χ
2/ν where ν is the number of degrees of freedom (here ν= N − 6).
‡ Post-fit χ2 probability computed with ν= N − 6.
3.4. Residuals to the HD 221287 orbital fit
The residuals to the orbital solution for HD 221287 presented in
Sect. 3.3 are clearly abnormal. Their weighted rms, 8.5 m s−1,
is much larger than the mean radial-velocity uncertainty ob-
tained for this target: 〈�RV〉= 2.1 m s−1. The abnormal scatter ob-
tained by quadratically correcting the residual rms for 〈�RV〉 is
8.2 m s−1. This matches the lowest value expected for this star
from the Santos et al. (2000) and Wright (2005) studies. Again,
we stress that these two studies clearly lack active F stars, and
their activity versus jitter relations are thus weakly constrained
for this kind of target. Our measured jitter value certainly does
not strongly disagree with their results.
We have searched for periodic signals in the radial-velocity
residuals by computing their Fourier transform, but no signifi-
cant peak in the power spectrum could be found. The absence of
significant periodicity is not surprising since the phase of star-
spot induced signals is not always conserved over more than a
few rotational cycles.
Cross-correlation function bisector spans are plotted against
the observed radial-velocity residuals in the bottom panel of
Fig. 4. A marginal anti-correlation (Spearman’s rank correlation
coefficient: ρ=−0.1) between the two quantities is visible. A
weighted linear regression (i.e the simplest possible model) was
computed. The obtained slope is only weakly significant (1σ).
We are thus unable, at this stage, to clearly establish the link be-
tween the line-profile variations and our residuals. As indicated
in Sect. 3.3, our orbital solution is not very well-constrained.
This probably affects the residuals and possibly explains the
absence of a clear anti-correlation. Additional radial-velocity
measurements are necessary for establishing this relation, but
activity-related processes so far remain the best explanation for
the observed abnormal residuals to the fitted orbit.
HD 221287 has a planet with an orbital period of 456 d but
with an additional radial-velocity signal, probably induced by
the presence of cool spots whose visibility is modulated by stel-
lar rotation.
4. Conclusion
We have presented our HARPS radial-velocity data for 3 Solar-
type stars: HD 100777, HD 190647, and HD 221287. The radial-
velocity variations detected for these stars are explained by the
presence of planetary companions. HD 100777 b has a minimum
mass of 1.16 MJup. Its orbit is eccentric (0.36) and has a period of
384 days. The 1038–day orbit of the 1.9 MJup planet around the
slightly evolved star HD 190647 is moderately eccentric (0.18).
The planetary companion inducing the detected velocity signal
for HD 221287 has a minimum mass of 3.1 MJup. Its orbit has
a period of 456 days. The orbital eccentricity for this planet is
not well-constrained. The fitted value is 0.08 but orbits with
0.0≤ e≤ 0.25 cannot be excluded yet. This rather weak con-
straint on the orbital shape is explained by two reasons. First,
our data cover the radial-velocity maximum poorly. Second, the
residuals to this orbit are abnormally large. We have tried to es-
tablish the relation between these high residuals and line-profile
variations through a study of the CCF bisectors. As expected, a
marginal anti-correlation of the two quantities is observed, but
it is only weakly significant, thereby preventing us from clearly
establishing the link between them.
Acknowledgements. The authors would like to thank the ESO–La Silla
Observatory Science Operations team for its efficient support during the observa-
tions and to all the ESO staff involved in the HARPS maintenance and techni-
cal support. Support from the Fundação para Ciência e a Tecnologia (Portugal)
to N.C.S. in the form of a scholarship (reference SFRH/BPD/8116/2002) and
a grant (reference POCI/CTEAST/56453/2004) is gratefully acknowledged.
Continuous support from the Swiss National Science Foundation is apprecia-
tively acknowledged. This research has made use of the Simbad database oper-
ated at the CDS, Strasbourg, France.
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	Introduction
	Stellar characteristics of HD100777, HD190647, and HD221287
	HARPS radial-velocity data
	A 1.16MJup planet around HD100777
	A 1.9MJup planet orbiting HD190647
	A 3.1MJup planetary companion to HD221287
	Residuals to the HD221287 orbital fit
	Conclusion

  The HARPS high-resolution high-accuracy spectrograph is offered to the
astronomical community since the second half of 2003. Since then, we have been
using this instrument for monitoring radial velocities of a large sample of
Solar-type stars (~1400 stars) in order to search for their possible low-mass
companions. Amongst the goals of our survey, one is to significantly increase
the number of detected extra-solar planets in a volume-limited sample to
improve our knowledge of their orbital elements distributions and thus obtain
better constraints for planet-formation models.
  In this paper, we present the HARPS radial-velocity data and orbital
solutions for 3 Solar-type stars: HD 100777, HD 190647, and HD 221287. The
radial-velocity data of HD 100777 is best explained by the presence of a 1.1
M_Jup planetary companion on a 384--day eccentric orbit (e=0.36). The orbital
fit obtained for the slightly evolved star HD 190647 reveals the presence of a
long-period (P=1038 d) 1.9 M_Jup planetary companion on a moderately eccentric
orbit (e=0.18). HD 221287 is hosting a 3.1 M_Jup planet on a 456--day orbit.
The shape of this orbit is not very well constrained because of our non-optimal
temporal coverage and because of the presence of abnormally large residuals. We
find clues for these large residuals to result from spectral line profile
variations probably induced by stellar activity related processes.

Introduction
The High Accuracy Radial-velocity Planet Searcher (HARPS,
Pepe et al. 2002, 2004; Mayor et al. 2003) was put in opera-
tion during the second half of 2003. HARPS is a high-resolution,
fiber-fed echelle spectrograph mounted on the 3.6–m telescope
at ESO–La Silla Observatory (Chile). It is placed in a vacuum
vessel and is accurately thermally-controlled (temperature varia-
tions are less than 1 mK over one night, less than 2 mK over one
month). Its most striking characteristic is its unequaled stability
and radial-velocity (RV) accuracy: 1 m s−1 in routine operations.
A sub-m s−1 accuracy can even be achieved for inactive, slowly
rotating stars when an optimized observing strategy aimed at
averaging out the stellar oscillations signal is applied (Santos
et al. 2004a; Lovis et al. 2006).
Send offprint requests to: D. Naef e-mail: dnaef@eso.org
? Based on observations made with the HARPS instrument on the
ESO 3.6-m telescope at the La Silla Observatory (Chile) under the GTO
programme ID 072.C-0488.
The HARPS Consortium that manufactured the instrument
for ESO has received Guaranteed Time Observations (GTO). The
core programme of the HARPS-GTO is a very high RV-precision
search for low-mass planets around non-active and slowly ro-
tating Solar-type stars. Another programme carried out by the
HARPS-GTO is a lower RV precision planet search. It is a survey
of about 850 Solar-type stars at a precision better than 3 m s−1.
The sample is a volume-limited complement (up to 57.5 pc) of
the CORALIE sample (Udry et al. 2000). The goal of this sub-
programme is to obtain improved Jupiter-sized planets orbital
elements distributions by substantially increasing the size of the
exoplanets sample. Statistically robust orbital elements distribu-
tions put strong constraints on the various planet formation sce-
narios. The total number of extra-solar planets known so far is
over 200. Nevertheless, some sub-categories of planets with spe-
cial characteristics (e.g. hot-Jupiters or very long-period planets)
are still weakly populated. The need for additional detections
thus remains high.
With typical measurement precisions of 2-3 m s−1, the
HARPS volume-limited programme does not necessarily aim at
2 D. Naef et al.: The HARPS search for southern extra-solar planets IX
Table 1. Observed and inferred stellar characteristics of
HD 100777, HD 190647, and HD 221287 (see text for details).
HD 100777 HD 190647 HD 221287
HIP 56572 99115 116084
Type K0 G5 F7V
mV 8.42 7.78 7.82
B − V 0.760 0.743 0.513
π [mas] 18.84± 1.14 18.44± 1.10 18.91± 0.82
d [pc] 52.8+3.4
−3.0 54.2
−3.1 52.9
MV 4.807 4.109 4.203
B.C. −0.119 −0.109 −0.010
L [L�] 1.05 1.98 1.66
Teff [K] 5582± 24 5628± 20 6304± 45
log g [cgs] 4.39± 0.07 4.18± 0.05 4.43± 0.16
[Fe/H] 0.27± 0.03 0.24± 0.03 0.03± 0.05
Vt [km s−1] 0.98± 0.03 1.06± 0.02 1.27± 0.12
M∗ [M�] 1.0± 0.1 1.1± 0.1 1.25± 0.10
log R
HK −5.03 −5.09 −4.59
Prot [d] 39± 2 39± 2 5.0± 2
age [Gyr] >2 >2 1.3
v sin i [km s−1] 1.8± 1.0 2.4± 1.0 4.1± 1.0
detecting very low-mass planetary companions, and it is mostly
sensitive to planets that are more massive than Saturn. To date,
it has already allowed the detection of several short-period pla-
nets: HD 330075 b (Pepe et al. 2004), HD 2638 b, HD 27894 b,
HD 63454 b (Moutou et al. 2005), and HD 212301 b (Lo Curto
et al. 2006).
In this paper, we report the detection of 3 longer-period pla-
netary companions orbiting stars in the volume-limited sample:
HD 100777 b, HD 190647 b, and HD 221287 b. In Sect. 2, we de-
scribe the characteristics of the 3 host stars. In Sect. 3, we present
our HARPS radial-velocity data and the orbital solutions for the
3 targets. In Sect. 3.4, we discuss the origin of the high residuals
to the orbital solution for HD 221287. Finally, we summarize our
findings in Sect. 4.
2. Stellar characteristics of HD 100777, HD 190647,
and HD 221287
The main characteristics of HD 100777, HD 190647, and
HD 221287 are listed in Table 1. Spectral types, apparent magni-
tudes mV, colour indexes B − V , astrometric parallaxes π, and
distances d are from the HIPPARCOS Catalogue (ESA 1997).
From the same source, we have also retrieved information on
the scatter in the photometric measurements and on the good-
ness of the astrometric fits for the 3 targets. The photometric
scatters are low in all cases. HD 190647 is flagged as a constant
star. The goodness-of-fit parameters are close to 0 for the 3 stars,
indicating that their astrometric data are explained by a single-
star model well. Finally, no close-in faint visual companions are
reported around these objects in the HIPPARCOS Catalogue.
We performed LTE spectroscopic analyses of high signal-
to-noise ratio (SNR) HARPS spectra for the 3 targets follow-
ing the method described in Santos et al. (2004b). Effective
temperatures (Teff), gravities (log g), iron abundances ([Fe/H]),
and microturbulence velocities (Vt) indicated in Table 1 re-
sult from these analyses. Like most of the planet-hosting stars
Table 2. HARPS radial-velocity data obtained for HD 100777.
Julian date RV Uncertainty
BJD− 2 400 000 [d] [km s−1]
53 063.7383 1.2019 0.0016
53 377.8740 1.2380 0.0015
53 404.7626 1.2205 0.0014
53 407.7461 1.2164 0.0014
53 408.7419 1.2176 0.0016
53 409.7891 1.2161 0.0015
53 468.6026 1.2109 0.0016
53 470.6603 1.2122 0.0021
53 484.6703 1.2273 0.0013
53 489.5948 1.2319 0.0022
53 512.5671 1.2494 0.0017
53 516.5839 1.2539 0.0014
53 518.5962 1.2554 0.0021
53 520.5778 1.2558 0.0022
53 543.5598 1.2649 0.0013
53 550.5289 1.2641 0.0016
53 573.4689 1.2682 0.0014
53 579.4705 1.2641 0.0022
53 724.8617 1.2520 0.0012
53 762.8169 1.2355 0.0013
53 765.7645 1.2311 0.0016
53 781.8894 1.2242 0.0016
53 789.7730 1.2209 0.0018
53 862.6200 1.2217 0.0015
53 866.6037 1.2239 0.0014
53 871.6270 1.2357 0.0015
53 883.5589 1.2397 0.0014
53 918.4979 1.2589 0.0017
53 920.5110 1.2613 0.0023
(Santos et al. 2004b), HD 100777 and HD 190647 have very high
iron abundances, more than 1.5 times the solar value, whereas
HD 221287 has a nearly solar metal content. Using the spec-
troscopic effective temperatures and the calibration in Flower
(1996), we computed bolometric corrections. Luminosities were
obtained from the bolometric corrections and the absolute ma-
gnitudes. The low gravity and the high luminosity of HD 190647
indicate that this star is slightly evolved. The other two stars
are still on the main sequence. Stellar masses M∗ were derived
from L, Teff , and [Fe/H] using Geneva and Padova evolutiona-
ry models (Schaller et al. 1992; Schaerer et al. 1993; Girardi
et al. 2000). Values of the projected rotational velocities, v sin i,
were derived from the widths of the HARPS cross-correlation
functions using a calibration obtained following the method de-
scribed in Santos et al. (2002, see their Appendix A) 1
Stellar activity indexes log R
HK (see the index definition
in Noyes et al. 1984) were derived from Ca II K line core re-
emission measurements on high-SNR HARPS spectra following
the method described in Santos et al. (2000). Using these va-
lues and the calibration in Noyes et al. (1984), we derived es-
timates of the rotational periods and stellar ages. The chromo-
spheric ages obtained with this calibration for HD 100777 and
HD 190647 are 6.2 and 7.6 Gyr. Pace & Pasquini (2004) have
shown that chromospheric ages derived for very low-activity,
Solar-type stars were not reliable. This is due to the fact that
the chromospheric emission drops rapidly after 1 Gyr and be-
comes virtually constant after 2 Gyr. For this reason, we have
chosen to indicate ages greater than 2 Gyr instead of the cali-
1 Using cross-correlation function widths for deriving projected rota-
tional velocities is a method that was first proposed by Benz & Mayor
(1981).
D. Naef et al.: The HARPS search for southern extra-solar planets IX 3
Fig. 1. Top: HARPS radial-velocity data (dots) for HD 100777
and fitted orbital solution (solid curve). The radial-velocity sig-
nal is induced by the presence of a 1.16 MJup planetary compan-
ion on a 384-day orbit. Bottom: Residuals to the fitted orbit. The
scatter of these residuals is compatible with the velocity uncer-
tainties.
brated values for these two stars. HD 221287 is much more active
and thus younger making its chromospheric age estimate more
reliable: 1.3 Gyr. We have also measured the lithium abundance
for this target following the method described in Israelian et al.
(2004) and again using a high-SNR HARPS spectrum. The mea-
sured equivalent width for the Li I λ6707.70Å line (deblended
from the Fe I λ6707.44Å line) is 66.6 mÅ leading to the fol-
lowing lithium abundance: log n(Li) = 2.98. Unfortunately, the
lithium abundance cannot provide any reliable age constraint in
our case. Studies of the lithium abundances of open cluster main
sequence stars have shown that log n(Li) remains constant and
equals ' 3 for Teff = 6300 K stars older than a few million years
(see for example Sestito & Randich 2005).
From the activity level reported for HD 221287
(log R
HK =−4.59), we can estimate the expected level of
activity-induced radial-velocity scatter (i.e. the jitter). Using
the results obtained by Santos et al. (2000) for stars with
similar activity levels and spectral types, the range of expected
jitter is between 8 and 20 m s−1. A similar study made on a
different stellar sample by Wright (2005) gives similar results:
an expected jitter of the order of 20 m s−1 (from the fit this
author presents in his Fig. 4). It has to be noted that both
studies contain very few F stars and even fewer high-activity
F stars. This results from the stellar sample they have used:
planet search samples selected against rapidly-rotating young
stars. Their predictions for the expected jitter level are therefore
not well-constrained for active F stars. Both HD 100777 and
HD 190647 are inactive and slowly rotating. Following the same
studies, low jitter values are expected in both cases: ≤ 8 m s−1.
Table 3. HARPS radial-velocity data obtained for HD 190647.
Julian date RV Uncertainty
BJD− 2 400 000 [d] [km s−1]
52 852.6233 −40.2874 0.0013
52 854.6727 −40.2868 0.0013
53 273.5925 −40.2435 0.0022
53 274.6041 −40.2354 0.0024
53 468.8874 −40.2688 0.0015
53 470.8634 −40.2689 0.0014
53 493.9234 −40.2700 0.0029
53 511.9022 −40.2723 0.0015
53 543.8020 −40.2785 0.0013
53 550.7721 −40.2804 0.0014
53 572.8074 −40.2818 0.0015
53 575.7266 −40.2844 0.0017
53 694.5136 −40.3056 0.0014
53 836.9226 −40.2982 0.0015
53 861.8630 −40.2950 0.0017
53 883.8224 −40.2907 0.0013
53 886.8881 −40.2883 0.0013
53 917.8390 −40.2785 0.0021
53 921.8472 −40.2785 0.0018
53 976.6039 −40.2623 0.0014
53 979.6654 −40.2610 0.0017
3. HARPS radial-velocity data
Stars belonging to the volume-limited HARPS-GTO sub-
programme are observed most of the time without the simulta-
neous Thorium-Argon reference (Baranne et al. 1996). The ob-
tained radial velocities are thus uncorrected for possible instru-
mental drifts. This only has a very low impact on our results
as the HARPS radial-velocity drift is less than 1 m s−1 over one
night. For this large volume-limited sample, we aim at a radial-
velocity precision of the order of 3 m s−1 (or better). This corres-
ponds roughly to an SNR of 40-50 at 5500Å. For bright targets
like the three stars of this paper, the exposure times required for
reaching this signal level can be very short as an SNR of 100
(at 5500Å) is obtained with HARPS in a 1-minute exposure on
a 6.5 mag G dwarf under normal weather and seeing conditions.
In order to limit the impact of observing overheads (telescope
preset, target acquisition, detector read-out), we normally do not
use exposure times less than 60 seconds. As a consequence, the
SNR obtained for bright stars is significantly higher than the tar-
geted one, and the output measurement errors are frequently be-
low 2 m s−1.
For our radial-velocity measurements, we consider two main
error terms. The first one is obtained through the HARPS Data
Reduction Software (DRS). It includes all the known calibration
errors (' 20 cm s−1), the stellar photon-noise, and the error on
the instrument drift. For observations taken with the simultane-
ous reference, the drift error is derived from the photon noise
of the Thorium-Argon exposure. For observations taken without
the lamp, a drift error term of 50 cm s−1 is quadratically added.
The second main error term is called the non-photonic error. It
includes guiding errors and a lower limit for the stellar pulsa-
tion signals. For the volume-limited programme, we use an ad-
hoc value for this term: 1.0 m s−1. Stellar noise (activity jitter,
pulsation signal) can of course be greater in some cases (as for
example for HD 221287, cf. Sect. 3.3). The non-photonic term
nearly vanishes for targets belonging to the very high RV pre-
cision sample (non-active stars, pulsation modes averaged out
by the specific observing strategy). In this latter case, this term
thus only contains the guiding errors: ' 30 cm s−1. The error bars
4 D. Naef et al.: The HARPS search for southern extra-solar planets IX
Fig. 2. Top: HARPS radial-velocity data (dots) for HD 190647
and fitted orbital solution (solid curve). The radial-velocity sig-
nal is induced by the presence of a 1.9 MJup planetary companion
on a 1038-day orbit. Bottom: Residuals to the fitted orbit. The
scatter of these residuals is compatible with the velocity uncer-
tainties.
listed in this paper correspond to the quadratic sum of the DRS
and the non-photonic errors.
In the following sections, we present the HARPS radial-
velocity data obtained for HD 100777, HD 190647, and
HD 221287 in more detail, as well as the orbital solutions fitted
to the data.
3.1. A 1.16 MJup planet around HD 100777
We have gathered 29 HARPS radial-velocity measurements of
HD 100777. These data span 858 days between February 27th
2004 (BJD = 2 453 063) and July 4th 2006 (BJD = 2 453 921).
Their mean radial-velocity uncertainty is 1.6 m s−1 (mean DRS
error: 1.3 m s−1). We list these measurements in Table 2 (elec-
tronic version only).
A nearly yearly signal is present in these data. We fit-
ted a Keplerian orbit. The resulting parameters are listed in
Table 5. The fitted orbit is displayed in Fig. 1, together with our
radial-velocity measurements. The radial-velocity data is best
explained by the presence of a 1.16 MJup planet on a 384 d fairly
eccentric orbit (e = 0.36). The inferred separation between the
host star and its planet is a = 1.03 AU. Both m2 sin i and a were
computed using a primary mass of 1 M�.
We performed Monte-Carlo simulations using the ORBIT
software (see Sect. 3.1. in Forveille et al. 1999) in order to
double-check the parameter uncertainties. The errorbars ob-
tained from these simulations are quasi-symmetric and some-
what larger ('18%) than the ones obtained from the covariance
matrix of the Keplerian fit. The errors we have finally quoted in
Table 5 are the Monte-Carlo ones. The residuals to the fitted orbit
(see bottom panel of Fig. 1) are flat and have a dispersion com-
patible with the measurement noise. The low reduced χ2 value
(1.45) and the χ2 probability (0.074) further demonstrate the
Table 4. HARPS radial-velocity data obtained for HD 221287.
Julian date RV Uncertainty
BJD− 2 400 000 [d] [km s−1]
52 851.8534 −21.9101 0.0012
52 853.8544 −21.9201 0.0021
52 858.7810 −21.9252 0.0019
53 264.7097 −21.8617 0.0021
53 266.6805 −21.8852 0.0020
53 268.7030 −21.8595 0.0034
53 273.6951 −21.8888 0.0031
53 274.7129 −21.8718 0.0021
53 292.6284 −21.9049 0.0020
53 294.6239 −21.8998 0.0019
53 295.6781 −21.9017 0.0024
53 296.6388 −21.9186 0.0026
53 339.6009 −21.9289 0.0015
53 340.5974 −21.9225 0.0013
53 342.5955 −21.9172 0.0013
53 344.5961 −21.9428 0.0014
53 345.5923 −21.9291 0.0013
53 346.5566 −21.9284 0.0013
53 546.9385 −21.8022 0.0039
53 550.9121 −21.8294 0.0022
53 551.9479 −21.7956 0.0018
53 723.5707 −21.8679 0.0033
53 727.5302 −21.8815 0.0021
53 862.9297 −21.9205 0.0023
53 974.7327 −21.8240 0.0021
53 980.7273 −21.8192 0.0022
good fit quality. The presence of another massive short-period
companion around HD 100777 is thus unlikely.
3.2. A 1.9 MJup planet orbiting HD 190647
Between August 1, 2003 (BJD = 2 452 852) and September 2,
2006 (BJD = 2 453 980), we obtained 21 HARPS radial-velocity
measurements for HD 190647. These data have a mean radial-
velocity uncertainty of 1.7 m s−1 (mean DRS error: 1.3 m s−1).
We list these measurements in Table 3 (electronic version only).
A long-period signal is clearly present in the RV data. We
performed a Keplerian fit. The resulting fitted parameters are
listed in Table 5. The fitted orbital period (1038 d) is slightly
shorter than the observing time span (1128 d) and the orbital
eccentricity is low (0.18). Monte-Carlo simulations were car-
ried out. The uncertainties on the orbital parameters obtained in
this case are nearly symmetric and a bit larger ('18%) than the
ones resulting from the Keplerian fit. In Table 5, we have listed
these more conservative Monte-Carlo uncertainties. The small
discrepancy between the two sets of errorbars is most probably
due to the rather short time span of the observations (only 1.09
orbital cycle covered) and to our still not optimal coverage of
both the minimum and the maximum of the radial-velocity orbit.
From the fitted parameters and with a primary mass of 1.1 M�,
we compute a minimum mass of 1.90 MJup for this planetary
companion. The computed separation between the two bodies
is 2.07 AU. Figure 2 shows our data and the fitted orbit.
The weighted rms of the residuals (1.6 m s−1) is slightly
smaller than the mean RV uncertainty. The low dispersion of the
residuals, the low reduced χ2 value, and its associated proba-
bility (0.11) allow us to exclude the presence of an additional
massive short-period companion.
D. Naef et al.: The HARPS search for southern extra-solar planets IX 5
Fig. 3. Top: HARPS radial-velocity data (dots) for HD 221287
and fitted orbital solution (solid curve). The detected Keplerian
signal is induced by a 3.1 MJup planet on a 456–day orbit.
Because of a non-optimal coverage of the radial-velocity maxi-
mum and the presence of stellar activity-induced jitter, the ex-
act shape of the orbit is not very well-constrained. Bottom:
Residuals to the fitted orbit. The scatter of these residuals is
much larger than the velocity uncertainties. This large dispersion
is probably due to the fairly high activity level of this star.
3.3. A 3.1 MJup planetary companion to HD 221287
A total of 26 HARPS radial-velocity data were obtained
for HD 221287. These data are spread over 1130 days: be-
tween July 31, 2003 (BJD = 2 452 851) and September 3, 2006
(BJD = 2 453 981). Unlike the two other targets presented in
this paper, a substantial fraction ('65%) of these velocities
were taken using the simultaneous Thorium-Argon reference.
They were thus corrected for the measured instrumental velocity
drifts. The mean radial-velocity uncertainty computed for this
data set is 2.1 m s−1 (mean DRS error: 1.8 m s−1). We list these
measurements in Table 4 (electronic version only).
A 456 d radial-velocity variation is clearly visible in our data
(see Fig. 3). This period is two orders of magnitude longer than
the rotation period obtained from the Noyes et al. (1984) cali-
bration for HD 221287: 5± 2 d. This large discrepancy between
PRV and Prot is probably sufficient for safely excluding stellar
spots as the origin of the detected RV signal, but we nevertheless
checked if this variability could be due to line-profile variations.
The cross-correlation function (CCF) bisector span versus radial
velocity plot is shown in the top panel of Fig. 4. The average
CCF bisector value is computed in two selected regions: near the
top of the CCF (i.e. near the continuum) and near its bottom (i.e
near the RV minimum). The span is the difference between these
two average values (top−bottom) and thus represents the overall
slope of the CCF bisector (for details, see Queloz et al. 2001).
As for the case of HD 166435 presented in Queloz et al.
(2001), an anti-correlation between spans and velocities is
expected in the case of star-spot induced line-profile varia-
tions. The bisector span data are quite noisy (weighted rms of
10.4 m s−1), but they are not correlated with the RV data. The
Fig. 4. a: Bisector span versus radial-velocity plot for
HD 221287. The dispersion of the span data is quite
large (10.4 m s−1) revealing potential line-profile variations.
Nevertheless, the main radial-velocity signal is not correlated
to these profile variations and is thus certainly of Keplerian
origin. b: Bisector span versus radial-velocity residuals to the
Keplerian orbit (see Table 5) displayed in the same velocity
scale. A marginal anti-correlation between the two quantities is
observed.
main signal can therefore not be due to line-profile variations
and certainly has a Keplerian origin.
Table 5 contains the results of a Keplerian fit that we per-
formed. Our data and the fitted orbit are displayed in Fig. 3. The
RV maximum remains poorly covered by our observations. As
for the other two targets, we made Monte-Carlo simulations for
checking our orbital parameter uncertainties. As expected, the
uncertainties obtained in this case largely differ from the ones
obtained via the Keplerian fit. For most of the parameters, the
errorbars resulting from the simulations are not symmetric and
much larger ('5 times larger). In order to be more conserva-
tive, we have chosen to quote these errors in Table 5. The shape
of the orbit is not very well-constrained, but there is no doubt
about the planetary nature of HD 221287 b. The fitted eccen-
tricity is low (0.08), but circular or moderately eccentric orbits
(up to 0.25) cannot be excluded yet. Using a primary mass of
1.25 M�, we compute the companion minimum mass and sepa-
ration: m2 sin i = 3.09 MJup and a = 1.25 AU.
6 D. Naef et al.: The HARPS search for southern extra-solar planets IX
Table 5. HARPS orbital solutions for HD 100777, HD 190647, and HD 221287.
HD 100777 HD 190647 HD 221287
P [d] 383.7± 1.2 1038.1± 4.9 456.1± +7.7
T [JD†] 456.2± 2.3 868± 24 263± +99
e 0.36± 0.02 0.18± 0.02 0.08± +0.17
−0.05
γ [km s−1] 1.246± 0.001 −40.267± 0.001 −21.858± +0.008
−0.005
ω [◦] 202.7± 3.1 232.5± 9.4 98± +92
K1 [m s−1] 34.9± 0.8 36.4± 1.2 71± +18−8
f (m) [10−9M�] 1.37± 0.10 4.94± 0.50 16.4± 12.6
a1 sin i [10−3AU] 1.15± 0.03 3.42± 0.12 2.95± 0.75
m2 sin i [MJup] 1.16± 0.03 1.90± 0.06 3.09± 0.79
a [AU] 1.03± 0.03 2.07± 0.06 1.25± 0.04
N 29 21 26
\ [m s−1] 1.7 1.6 8.5
χ2red
? 1.45 1.46 26.7
p(χ2, ν)‡ 0.074 0.11 0
† JD = BJD− 2 453 000
\ σO−C is the weighted rms of the residuals (weighted by 1/�2, where � is the O−C uncertainty)
? χ2red = χ
2/ν where ν is the number of degrees of freedom (here ν= N − 6).
‡ Post-fit χ2 probability computed with ν= N − 6.
3.4. Residuals to the HD 221287 orbital fit
The residuals to the orbital solution for HD 221287 presented in
Sect. 3.3 are clearly abnormal. Their weighted rms, 8.5 m s−1,
is much larger than the mean radial-velocity uncertainty ob-
tained for this target: 〈�RV〉= 2.1 m s−1. The abnormal scatter ob-
tained by quadratically correcting the residual rms for 〈�RV〉 is
8.2 m s−1. This matches the lowest value expected for this star
from the Santos et al. (2000) and Wright (2005) studies. Again,
we stress that these two studies clearly lack active F stars, and
their activity versus jitter relations are thus weakly constrained
for this kind of target. Our measured jitter value certainly does
not strongly disagree with their results.
We have searched for periodic signals in the radial-velocity
residuals by computing their Fourier transform, but no signifi-
cant peak in the power spectrum could be found. The absence of
significant periodicity is not surprising since the phase of star-
spot induced signals is not always conserved over more than a
few rotational cycles.
Cross-correlation function bisector spans are plotted against
the observed radial-velocity residuals in the bottom panel of
Fig. 4. A marginal anti-correlation (Spearman’s rank correlation
coefficient: ρ=−0.1) between the two quantities is visible. A
weighted linear regression (i.e the simplest possible model) was
computed. The obtained slope is only weakly significant (1σ).
We are thus unable, at this stage, to clearly establish the link be-
tween the line-profile variations and our residuals. As indicated
in Sect. 3.3, our orbital solution is not very well-constrained.
This probably affects the residuals and possibly explains the
absence of a clear anti-correlation. Additional radial-velocity
measurements are necessary for establishing this relation, but
activity-related processes so far remain the best explanation for
the observed abnormal residuals to the fitted orbit.
HD 221287 has a planet with an orbital period of 456 d but
with an additional radial-velocity signal, probably induced by
the presence of cool spots whose visibility is modulated by stel-
lar rotation.
4. Conclusion
We have presented our HARPS radial-velocity data for 3 Solar-
type stars: HD 100777, HD 190647, and HD 221287. The radial-
velocity variations detected for these stars are explained by the
presence of planetary companions. HD 100777 b has a minimum
mass of 1.16 MJup. Its orbit is eccentric (0.36) and has a period of
384 days. The 1038–day orbit of the 1.9 MJup planet around the
slightly evolved star HD 190647 is moderately eccentric (0.18).
The planetary companion inducing the detected velocity signal
for HD 221287 has a minimum mass of 3.1 MJup. Its orbit has
a period of 456 days. The orbital eccentricity for this planet is
not well-constrained. The fitted value is 0.08 but orbits with
0.0≤ e≤ 0.25 cannot be excluded yet. This rather weak con-
straint on the orbital shape is explained by two reasons. First,
our data cover the radial-velocity maximum poorly. Second, the
residuals to this orbit are abnormally large. We have tried to es-
tablish the relation between these high residuals and line-profile
variations through a study of the CCF bisectors. As expected, a
marginal anti-correlation of the two quantities is observed, but
it is only weakly significant, thereby preventing us from clearly
establishing the link between them.
Acknowledgements. The authors would like to thank the ESO–La Silla
Observatory Science Operations team for its efficient support during the observa-
tions and to all the ESO staff involved in the HARPS maintenance and techni-
cal support. Support from the Fundação para Ciência e a Tecnologia (Portugal)
to N.C.S. in the form of a scholarship (reference SFRH/BPD/8116/2002) and
a grant (reference POCI/CTEAST/56453/2004) is gratefully acknowledged.
Continuous support from the Swiss National Science Foundation is apprecia-
tively acknowledged. This research has made use of the Simbad database oper-
ated at the CDS, Strasbourg, France.
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	Introduction
	Stellar characteristics of HD100777, HD190647, and HD221287
	HARPS radial-velocity data
	A 1.16MJup planet around HD100777
	A 1.9MJup planet orbiting HD190647
	A 3.1MJup planetary companion to HD221287
	Residuals to the HD221287 orbital fit
	Conclusion
