[Paper Review] The EXOTIME project: a status report on PG 1325+101 (QQ Vir)

S. Benatti, R. Silvotti+8 more|arXiv (Cornell University)|Dec 3, 2010

Superconducting Materials and Applications3 citations

TL;DR

The EXOTIME project investigates planetary companions around pulsating subdwarf B stars using the timing method, focusing on PG 1325+101 (QQ Vir) over two years of photometric monitoring. Preliminary O-C diagrams for the main pulsation frequency show phase coherence in V-band data but inconsistent results in B-band due to sparse coverage, indicating the need for improved data sampling to detect orbital perturbations.

ABSTRACT

After the discovery of V391 Peg b, the first planet detected around a post Red Giant phase star (Silvotti et al. 2007), the EXOTIME (EXOplanet search with the TIming MEthod) project is focused on the search for new planets with similar characteristics. The aim of the project is to organize a global observing network to collect as much data as possible for a sample of five subdwarf B (sdB) stars and share them in order to obtain a more precise analysis. These evolved pulsators may have extremely regular oscillation periods. This feature makes these stars suitable to search for planetary companions with the timing method as in the case of pulsars. In this contribution we present the project and some preliminary results for the star PG 1325+101 (QQ Vir) after the first two years of activity.

Motivation & Objective

• To detect substellar companions around evolved subdwarf B stars using long-term photometric timing.
• To test the feasibility of the timing method for low-mass, wide-orbit planets around pulsating sdB stars.
• To improve the understanding of sdB star evolution through asteroseismic and orbital parameter analysis.
• To establish a global network for coordinated, long-term monitoring of pulsating sdB stars.
• To assess the potential role of planetary companions in enhancing mass loss during the red giant branch phase.

Proposed method

• Utilizes the O-C (Observed minus Calculated) diagram technique to detect phase and period variations in pulsation frequencies.
• Applies barycentric correction and standardizes differential photometric flux in milli-modulation intensity (mmi) units.
• Fixes known pulsation frequencies from prior studies (e.g., Silvotti et al. 2006; Baran et al. 2010) to compute mean phases.
• Performs sinusoidal fitting to phase differences to estimate time-lags and detect periodic shifts indicative of orbital companions.
• Combines multi-site, multi-season photometric data from B and V bands to improve phase coherence and reduce uncertainties.
• Uses formal error estimates from Montgomery & O’Donoghue (1999) for uncertainty quantification in O-C diagrams.

Experimental results

Research questions

• RQ1 Can the timing method detect planetary companions around PG 1325+101 with current data coverage?
• RQ2 How stable are the pulsation phases of PG 1325+101 over multiple observing seasons?
• RQ3 What is the impact of sparse or uneven B-band coverage on the reliability of O-C diagram analysis?
• RQ4 Can the V-band long-duration run (95.5 hours) provide a stable reference for phase coherence in the absence of B-band data?
• RQ5 What are the implications of phase and amplitude variations for the presence of a planetary companion or internal stellar processes?

Key findings

• No infrared excess is detected in the spectral energy distribution of PG 1325+101, ruling out a cool stellar companion.
• The O-C diagram for the V-band monitoring (95.5 hours) shows good phase coherence over the observation period.
• B-band O-C results from 2008 show phase stability but are hampered by large uncertainties, particularly for the second data point.
• The combination of B and V band data remains inconsistent, suggesting insufficient coverage to derive a unique solution.
• The 2009 data set shows similar challenges, with preliminary analysis indicating the need for more data to resolve phase ambiguities.
• The project identifies that improved data sampling across seasons is essential to link observations and achieve reliable detection of orbital perturbations.