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Title:
Millimagnitude Photometry for Transiting Extrasolar Planetary Candidates. IV. Solution to the Puzzle of the Extremely Red OGLE-TR-82 Primary
Authors:
Hoyer, Sergio; Ramírez Alegría, Sebastián; Ivanov, Valentin D.; Minniti, Dante; Pietrzyński, Grzegorz; Ruíz, María Teresa; Gieren, Wolfgang; Udalski, Andrzej; Zoccali, Manuela; Carrasco, Eleazar Rodrigo; Díaz, Rodrigo F.; Fernández, José Miguel; Gallardo, José; Rejkuba, Marina; Pérez, Felipe
Affiliation:
AA(Departamento de Astronomía, Universidad de Chile, Las Condes, Santiago, Chile; .; Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago 22, Chile.), AB(Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago 22, Chile.), AC(European Southern Observatory, Vitacura, Santiago 19, Chile.), AD(Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago 22, Chile.), AE(Departamento de Física, Universidad de Concepción, Concepción, Chile.; Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, 00-478 Warsaw, Poland.), AF(Departamento de Astronomía, Universidad de Chile, Las Condes, Santiago, Chile; .), AG(Departamento de Física, Universidad de Concepción, Concepción, Chile.), AH(Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, 00-478 Warsaw, Poland.), AI(Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago 22, Chile.), AJ(Gemini Observatory, Southern Operations Center, La Serena, Chile.), AK(Instituto de Astronomía y Física del Espacio, CONICET, Universidad de Buenos Aires, C1428ZAA Buenos Aires, Argentina.), AL(Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago 22, Chile.; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138.), AM(Centre de Recherche Astronomique de Lyon, Ecole Normale Supérieure de Lyon, F-69364 Lyon, France.), AN(European Southern Observatory, D-85748 Garching, Germany.), AO(Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago 22, Chile.)
Publication:
The Astrophysical Journal, Volume 669, Issue 2, pp. 1345-1353. (ApJ Homepage)
Publication Date:
11/2007
Origin:
UCP
ApJ Keywords:
Planets and Satellites: Formation, stars: individual (OGLE-TR-82)
DOI:
10.1086/520871
Bibliographic Code:
2007ApJ...669.1345H

Abstract

We present precise new V-, I-, and Ks-band photometry for the planetary-transit candidate star OGLE-TR-82. V-band images acquired in good seeing with the VIMOS instrument at the Very Large Telescope allowed us to measure V=20.61+/-0.03 mag for this star despite the presence of a brighter neighbor about 1" away. This faint magnitude answers the question why it has not been possible to measure radial velocities for this object. One transit of this star has been observed with the GMOS-S instrument on Gemini South in the i and g bands, which allowed us to verify that this is not a false positive, to confirm the transit amplitude measured by OGLE, and to improve the ephemeris. The transit is better defined in the i-band light curve (with a depth of Ai=0.034 mag), than in the g band (Ag=0.1 mag), in which the star is significantly fainter. Near-IR photometry obtained with the SOFI array at the ESO New Technology Telescope yields K=12.20+/-0.10 and V-K=8.40+/-0.10, so red that it is unlike any transit candidate studied before. With the new data, we consider two possible configurations for the system: (1) a nearby M7 V star or (2) a blend with a very reddened, distant red giant. The first hypothesis would give a radius for the companion of Rp=0.3+/-0.1 RJ, i.e., the size of Neptune. Quantitative analysis of near-IR spectroscopy finally shows that OGLE-TR-82 is a distant, reddened, metal-poor early K giant, confirmed by direct comparison with stellar templates, which gives as a best match a K3 III star. Therefore, we rule out a planetary nature for the companion, and conclude that this system is a main-sequence binary blended with a background red giant. As a case study, a system that can so mimic a planetary transit presents a lesson for future transit surveys.

Based on observations collected with the Gemini South telescope (queue observing, program GS-2005B-Q-9) and with the Very Large Telescope at Paranal Observatory (J. M. F. and D. M., Visiting Astronomers) and the ESO New Technology Telescope at La Silla Observatory (S. R., F. P., and D. M., Visiting Astronomers) for ESO programs 075.C-0427, 075.B-0414, and 076.C-0122.

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