[Paper Review] Extrasolar planets and brown dwarfs around AF-type stars. X.The SOPHIE northern sample. Combining the SOPHIE and HARPS surveys to compute the close giant planet mass-period distribution around AF-type stars

S. Borgniet, A.‐M. Lagrange+32 more|arXiv (Cornell University)|Sep 26, 2018

Stellar, planetary, and galactic studies13 citations

TL;DR

This study combines radial velocity data from the SOPHIE and HARPS surveys to characterize close giant planet and brown dwarf populations around 125 northern main-sequence AF-type stars. It finds a Jupiter-mass planet occurrence rate of 3.7% (−1/+3%) within 2–3 au for stars with masses <1.5 M☉, with upper limits of 4% for brown dwarfs and 3–4.5% for short-period planets, consistent with trends in FGK stars and suggesting possible migration differences with stellar mass.

ABSTRACT

The impact of the stellar mass on the giant planet properties is still to be fully understood. Main-Sequence (MS) stars more massive than the Sun remain relatively unexplored in radial velocity (RV) surveys, due to their characteristics that hinder classical RV measurements. Our aim is to characterize the close (up to 2.5 au) giant planet (GP) and brown dwarf (BD) population around AF MS stars and compare this population to stars with different masses. We used the SOPHIE spectrograph located on the 1.93m telescope at Observatoire de Haute-Provence to observe 125 northern, MS AF dwarfs. We used our dedicated SAFIR software to compute the RV and other spectroscopic observables. We characterized the detected sub-stellar companions and computed the GP and BD occurrence rates combining the present SOPHIE survey and a similar HARPS survey. We present new data on two known planetary systems around the F5-6V dwarfs HD16232 and HD113337. For the latter, we report an additional RV variation that might be induced by a second GP on a wider orbit. We also report the detection of fifteen binaries or massive sub-stellar companions with high-amplitude RV variations or long-term RV trends. Based on 225 targets observed with SOPHIE or HARPS, we constraint the BD frequency within 2-3 au around AF stars to be below 4 percents (1-sigma). For Jupiter-mass GP within 2-3 au (periods below 1000 days), we found the occurrence rate to be 3.7 (+3/-1) percents around AF stars with masses below 1.5 solar masses, and to be below 6 percents around AF stars with masses above 1.5 solar masses. For periods smaller than 10 days, we find the GP occurrence rate to be below 3 or 4.5 percents, respectively. Our results are compatible with the GP frequency reported around FGK dwarfs and are compatible with a possible increase of GP orbital periods with the stellar mass as predicted by formation models.

Motivation & Objective

• To characterize the close (up to ~2 au) giant planet and brown dwarf population around main-sequence AF-type stars, which are underexplored in radial velocity surveys.
• To investigate how stellar mass influences the occurrence rate of giant planets and brown dwarfs, particularly in comparison to FGK-type stars.
• To determine the frequency of hot Jupiters and massive substellar companions around AF stars using high-precision radial velocity measurements.
• To combine SOPHIE and HARPS data to improve statistical constraints on planetary occurrence rates in the 1–3 au orbital range.
• To assess the compatibility of observed occurrence rates with theoretical models of planet formation and migration as a function of stellar mass.

Proposed method

• Conducted radial velocity monitoring of 125 northern main-sequence AF-type stars using the SOPHIE spectrograph on the 1.93m telescope at Observatoire de Haute-Provence.
• Applied the S AFIR software pipeline to compute radial velocities and spectroscopic indicators (e.g., CCF, FWHM) to detect planetary signals and stellar companions.
• Combined SOPHIE data with the HARPS survey from Paper IX to increase sample size and statistical power for occurrence rate calculations.
• Used statistical methods to compute false alarm probabilities and derive upper limits on occurrence rates, accounting for detection completeness.
• Classified detected signals based on RV amplitude, orbital period, and additional indicators (e.g., bisector span, correlation function shape) to distinguish planets from stellar binaries.
• Calculated occurrence rates for giant planets (1 < m_p sin i < 13 M_Jup) and brown dwarfs within 2–3 au, splitting results by stellar mass (<1.5 M☉ vs. >1.5 M☉) and orbital period.

Experimental results

Research questions

• RQ1 What is the occurrence rate of giant planets (1 < m_p sin i < 13 M_Jup) within 2–3 au around main-sequence AF-type stars with masses <1.5 M☉?
• RQ2 How does the occurrence rate of brown dwarfs within 2–3 au around AF-type stars compare to that around FGK-type stars or evolved subgiants?
• RQ3 Is there a significant population of hot Jupiters (P < 10 days) around AF-type stars, and how does this compare to the frequency around solar-type stars?
• RQ4 Do the observed occurrence rates of close substellar companions around AF stars support theoretical predictions of increased orbital periods with increasing stellar mass?
• RQ5 How do the results from the SOPHIE survey compare with those from the HARPS survey when combined, and what is the statistical significance of the derived upper limits?

Key findings

• The occurrence rate of Jupiter-mass planets (1 < m_p sin i < 13 M_Jup) within 2–3 au for AF stars with masses <1.5 M☉ is 3.7% with a 90% credible interval of −1 to +3%.
• For AF stars with masses >1.5 M☉, the upper limit on the occurrence rate of Jupiter-mass planets within 2–3 au is ≤6% at 1σ confidence.
• The brown dwarf occurrence rate within 2–3 au around AF stars is constrained to be below 4% at 1σ confidence, consistent with lower limits from white dwarf and subgiant surveys.
• The occurrence rate of giant planets with orbital periods <10 days is constrained to be below 3–4.5% at 1σ, with no hot Jupiters detected in the 225-target sample.
• The observed occurrence rates for AF stars are compatible with those reported for FGK dwarfs, suggesting no strong enhancement in planet frequency with increasing stellar mass in this range.
• The lack of detected hot Jupiters and the low occurrence rates for short-period planets are consistent with theoretical models predicting that higher-mass stars may host planets on longer-period orbits due to reduced migration efficiency.