Using the Sun to estimate Earth-like planets detection capabilities II. Impact of plages

Astronomy and Astrophysics (Impact Factor: 5.08). 01/2010; DOI: 10.1051/0004-6361/200913551
Source: arXiv

ABSTRACT Stellar activity produced by spots and plages affects the radial velocity (RV) signatures. Because even low activity stars would produce such a signal, it is crucial to determine how it influences our ability to detect small planetary signals such as those produced by Earth-mass planets in the habitable zone (HZ). In a recent paper, we investigated the impact of sunlike spots. We aim here to investigate the additional impact of plages. We used the spot and plage properties over a solar cycle to derive the RV that would be observed if the Sun was seen edge-on. The RV signal comes from the photometric contribution of spots and plages and from the attenuation of the convective blueshift in plages. We compared the RV signal with the signal that would be produced by an Earth-mass planet in the HZ. We find that the photometric contributions of spots and plages to the RV signal partially balance each other out, so that the residual signal is comparable to the spot signal. However, the plage contribution due to the convective blueshift attenuation dominates the total signal, with an amplitude over the solar cycle of about 8-10 m/s. This contribution is very strongly correlated with the Ca index on the long term, which may be a way to distinguish between stellar activity and a planet. Providing a very good temporal sampling and signal-to-noise ratio, the photometric contribution of plages and spots should not prevent detection of Earth-mass planets in the HZ. However, the convection contribution makes such a direct detection impossible, unless its effect can be corrected for by methods that still need to be found. We show that it is possible to identify the convection contribution if the sensitivity is good enough, for example, by using activity indicators. Comment: 15 pages, 14 figures, accepted in Astronomy and Astrophysics

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    ABSTRACT: Aims: It is known that stellar spots may in some cases produce radial velocity (RV) signatures similar to those of exoplanets. To date, the most extensive set of data on spots, active regions, and activity in general for any star is that obtained for the Sun. To investigate the impact of these spots, we aim to study the detectability of Earth-mass planets in the habitable zone (HZ) of solar-type stars, if covered by spots similar to sunspots. Methods: We used the sunspot properties recorded over one solar cycle between 1993 and 2003 to infer the RV curve that a solar-type star seen edge-on would exhibit, if covered by these spots. We also derive interesting parameters such as bisector velocity span (BVS) and photometric curves, commonly used in the analysis of RV data. We compare the obtained data with archival solar data available for the same epoch (e.g., irradiance, Ca index). We also simulate the RV of such a spotted star surrounded by an Earth-mass planet located in the HZ. Results: The RV of the spotted star appears to be very variable, in a complex way, depending on the activity level, with amplitudes from a few tens cm/s up to 5 m/s (assuming DeltaTs = T&sun; - Tspot = 550 K). A correlation between the BVS and the RV data is observed even when several spots are present with a slope so small that only data of very high precision (better than 5 cm/s) can enable its detection. Photometric variations of up to 0.5% are predicted, depending on the level of activity, in agreement with measured solar photometric variations. Based on present assumptions, the detection of a 1 MEarth planet located between 0.8 and 1.2 AU requires intensive monitoring (weekly or more frequent), over several years. The temporal sampling is more crucial than the data precision (assuming precisions in the range [1-10] cm/s). Cooler spots may become a problem for these detections. We also anticipate that plages, not considered in this paper, could further complicate or even compromise such detections.
    Astronomy and Astrophysics 03/2010; 512. · 5.08 Impact Factor
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    ABSTRACT: We present here a new observational technique, Phase Closure Nulling (PCN), which has the potential to obtain very high contrast detection and spectroscopy of faint companions to bright stars. PCN consists in measuring closure phases of fully resolved objects with a baseline triplet where one of the baselines crosses a null of the object visibility function. For scenes dominated by the presence of a stellar disk, the correlated flux of the star around nulls is essentially canceled out, and in these regions the signature of fainter, unresolved, scene object(s) dominates the imaginary part of the visibility in particular the closure phase. We present here the basics of the PCN method, the initial proof-of-concept observation, the envisioned science cases and report about the first observing campaign made on VLTI/AMBER and CHARA/MIRC using this technique. Comment: To be published in the proceedings of the SPIE'2010 conference on "Optical and Infrared Interferometry II"
    Proc SPIE 07/2010;


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