The corona of HD 189733 and its X-ray activity

Journal Article · Sun Apr 20 00:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/785/2/145· OSTI ID:22357071

Pillitteri, I.; Wolk, S. J.; Günther, H. M.; Cohen, O.; Kashyap, V.; Drake, J. J. ^[1]; Lopez-Santiago, J. ^[2]; Sciortino, S. ^[3]

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1. SAO, 60 Garden Street, Cambridge, MA 02138 (United States)
2. AEGORA, Facultad de CC. Matemáticas, Universidad Complutense de Madrid, Plaza de Ciencias 3, E-28040 Madrid (Spain)
3. INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy)

Testing whether close-in massive exoplanets (hot Jupiters) can enhance the stellar activity in their host primary is crucial for the models of stellar and planetary evolution. Among systems with hot Jupiters, HD 189733 is one of the best studied because of its proximity, strong activity, and the presence of a transiting planet, which allows transmission spectroscopy and a measure of the planetary radius and its density. Here we report on the X-ray activity of the primary star, HD 189733 A, using a new XMM-Newton observation and a comparison with the previous X-ray observations. The spectrum in the quiescent intervals is described by two temperatures at 0.2 keV and 0.7 keV, while during the flares a third component at 0.9 keV is detected. With the analysis of the summed Reflection Grating Spectrometer spectra, we obtain estimates of the electron density in the range n{sub e} = (1.6-13) × 10{sup 10} cm{sup –3}, and thus the corona of HD 189733 A appears denser than the solar one. For the third time, we observe a large flare that occurred just after the eclipse of the planet. Together with the flares observed in 2009 and 2011, the events are restricted to a small planetary phase range of φ = 0.55-0.65. Although we do not find conclusive evidence of a significant excess of flares after the secondary transits, we suggest that the planet might trigger such flares when it passes close to the locally high magnetic field of the underlying star at particular combinations of stellar rotational phases and orbital planetary phases. For the most recent flares, a wavelet analysis of the light curve suggests a loop of length of four stellar radii at the location of the bright flare, and a local magnetic field of the order of 40-100 G, in agreement with the global field measured in other studies. The loop size suggests an interaction of magnetic nature between planet and star, separated by only ∼8R {sub *}. The X-ray variability of HD 189733 A is larger than the variability of field stars and young Pleiades of similar spectral type and X-ray luminosity. We also detect the stellar companion (HD 189733 B, ∼12'' from the primary star) in this XMM-Newton observation. Its very low X-ray luminosity (L{sub X} = 3.4 × 10{sup 26} erg s{sup –1}) confirms the old age of this star and of the binary system. The high activity of the primary star is best explained by a transfer of angular momentum from the planet to the star.

• OSTI ID: 22357071
• Journal Information: Astrophysical Journal, Vol. 785, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ANGULAR MOMENTUM
COMPARATIVE EVALUATIONS
DENSITY
ECLIPSE
ELECTRON DENSITY
INTERACTIONS
KEV RANGE
LUMINOSITY
MAGNETIC FIELDS
REFLECTION
SOLAR SYSTEM EVOLUTION
SPECTRA
SPECTROMETERS
SPECTROSCOPY
STARS
STELLAR ACTIVITY
STELLAR CORONAE
TRANSMISSION
VISIBLE RADIATION
X RADIATION