En este trabajo medimos la intensidad de las bandas moleculares CN y CH en una muestra de estrellas con y sin exoplanetas (indices δS3839, δS4142 y δCH4300). El índice δS3839 parece ser menor en estrellas sin exoplanetas. El hecho de que la banda CN aumente con la metalicidad, puede explicar al menos en parte las diferentes distribuciones observadas en estrellas con y sin exoplanetas. Advertimos que hasta el momento las muestras son relativamente pequeñas.We measured the strength of CN and CH molecular bands in a sample of stars with and without exoplanets (indices δS3839, δS4142 and δCH4300). The index δS3839 seem to present smaller values for stars without exoplanets. No correlation is found between molecular bands and exoplanet parameters, supporting the primordial hypothesis of planet formation. The CN band strength seem to increase with C, N and Fe abundances. This could explain at least in part the dissimilar distributions of CN observed for stars with and without exoplanets. We caution that this is an initial result based in relatively small number of objects.Fil: Saffe, Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Jofre, Jorge Emiliano. Universidad Nacional de Córdoba; ArgentinaFil: Petrucci, Romina. Universidad Nacional de Córdoba; Argentin

Jofre, Jorge Emiliano

Petrucci, Romina Paola

Saffe, Carlos

English

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Asociación Argentina de AstronomíaBAAA, Vol. 54, 2011J.J. Clariá, P. Benaglia, R. Barbá, A.E. Piatti & F.A. Bareill s, eds.PRESENTACIÓN MURALCN and CH bands in exoplanet host starsC. Saffe1, E. Jofré1 & R. Petrucci1(1) Instituto de Cs. Astronómicas, de la Tierra y del Espacio(ICATE)Abstract. We measured the strength of CN and CH molecular bands in a sam-ple of stars with and without exoplanets (indicesδS3839,δS4142 andδCH4300).The indexδS3839 seem to present smaller values for stars without exoplanets.No correlation is found between molecular bands and exoplanet parameters,supporting the primordial hypothesis of planet formation.The CN band strengthseem to increase with C, N and Fe abundances. This could explain at least inpart the dissimilar distributions of CN observed for stars with and without exo-planets. We caution that this is an initial result based in relatively small numberof objects.Resumen. En este trabajo medimos la intensidad de las bandas molecular sCN y CH en una muestra de estrellas con y sin exoplanetas (indicesδS3839,δS4142 yδCH4300). El índiceδS3839 parece ser menor en estrellas sin exopla-netas. El hecho de que la banda CN aumente con la metalicidad,pue e explicaral menos en parte las diferentes distribuciones observadasen e trellas con y sinexoplanetas. Advertimos que hasta el momento las muestras son relativamentepequeñas.1. IntroductionMain-sequence exoplanet host (EH) stars are, on average, metal-rich in comparison tono-EH stars (e.g. Santos et al. 2004). Fischer & Valenti (2005) showed that the probabi-lity to present an exoplanet increase with the metallicity of the star. On the other hand,the molecular content in the atmospheres of EH stars does notreceived the same atten-tion in literature. In particular, molecular bands of CN andCH are readily observed inthe spectra of solar-type stars.Different molecules are commonly detected in protoplanetary disks, such as brightlines of CO and HCO+. Also lines of DCO+, CN, HCN, CCH and other molecularspecies are observed (see e.g. the review of van Dishoeck 2009). Different works showsthat molecules are present in protoplanetary disks and could be important ingredientsin the planet formation.Then, the aim of this work is to directly compare (to our knowledge, for the firsttime) the molecular strengths in the atmospheres of stars with and without low-masscompanions or exoplanets. This study will help to determineif the strength of certainmolecular bands observed in main-sequence stars could playa role in the planet for-mation process. Also we search for possible correlations between the molecular indicesand exoplanet parameters (semi-major axis a, eccentricitye and planet mass m seni).4950 C. Saffe et al.This comparison allow us to support the primordial scenarioof planet formation, fo-llow a reasoning similar to Bond et al. (2006). In this scenario the abundance content ofthe star is similar to their original parent cloud. However,we caution that the accretionhypothesis (i.e. the increase of abundances due to externalpollution of material) couldnot be totally excluded.2. Observational materialWe observed 38 southern EH stars from the California and Carnegie and the GenevaObservatory planet search lists1. The 38 stars we observed have V magnitude between1.5 and 8.9 and spectral types FGK (5, 26 and 7 objects, respectively), as specified inthe Hipparcos database. We also observed a sample of 19 starsno known to have anyplanetary-mass companions (Santos et al. 2004, Bond et al. 2008, Gilli et al. 2006). The19 stars we observed have V magnitude between 2.8 and 8.3 and spectral types FGK (2,11 and 6 objects, respectively). The stars studied in this work d not present IR excessindicative of circumstellar dust.The spectra were obtained at Complejo Astrónomico El Leoncit (CASLEO) bet-ween April 21 and 25, 2008 and October 10 and 15, 2010. We used the 2.15 m telescopeequipped with a REOSC echelle spectrograph and a TEK 1024x10CCD detector. Wehave used a grating with 400 lines mm−1. The spectra cover a range 3500-6500Å andthe S/N ratio is∼150. The data were reduced using IRAF procedures and thesbandstask was used to measure the strength of the molecular bands.3. Spectral indicesWe measure the strength of 2 CN bands at∼3883 Å,∼4215 Å and a CH band at∼4300Å using the spectral indices S3839, S4142 and CH4300 defined in literature (e.g. Har-beck et al. 2003). The index definitions are:S3839= -2.5 log F3861−3884F3894−3910,S4142= -2.5 log F4120−42160.5F4055−4080+0.5F4240−4280,CH4300= -2.5 log F4285−43150.5F4240−4280+0.5F4390−4460,where F3861−3884, for instance, is the summed spectral flux in ADU counts from 3861to 3884 Å. To determine the uncertainty, we assumed pure photon noise statistics andadded the dispersion of the indices derived from individualspectra. The average dis-persions are 0.151, 0.098 and 0.064 for S3839, S4142 and CH4300, respectively. Weapplied a temperature and gravity correction similar to Harbeck et al. (2003) and refe-rred the corrected indices to asδS3819,δS4142 andδCH4300.There is a general agreement between theδS3839 andδS4142 values, howeverS4142 is less sensitive to the intensity of the CN molecule (Harbeck et al. 2003, Pancinoet al. 2010). Then, we adopt the index S3839 to measure the strength of the CN band,similar to these literature works.1http://exoplanets.org, http://obswww.unige.ch/exoplanetsCN and CH bands in exoplanet host stars 51Figura 1. Distribution of the indicesδCH4300 andδS3839. EH and no-EH starsare showed by filled and empty histograms, respectively.4. Molecular bands in EH and no-EH starsWe present in the Figure 1 the distribution of the indicesδCH4300 andδS3839. EHand no-EH stars are showed by filled and empty histograms, respectively. In the Ta-ble 1 we present the average and dispersion of the indices. The Figure 1 and the Table1 shows that the distribution ofδCH4300 values for EH and no-EH stars are simi-lar. However, forδS3839 no-EH stars seem to concentrate in relatively smallervalues(δS3839<∼0.6). The difference is also present in the values of Table 1.A Kolmogorov-Smirnov test gives a probability of%20 that both distributions represent the same po-pulation. We caution that this is an initial result and more stars are needed to verify asignificative difference.No clear relation is apparent between molecular indices andexoplanet parameters(a, e and m seni), which is naturally explained by the primordial scenario of planetformation (e.g. Bond et al. 2006). However, the accretion hypothesis could not be totallyexcluded.5. Carbon abundances from atomic linesThe stellar parameters Teff , log g, [Fe/H] andξ (microturbulence velocity) have beenderived by requiring excitation and ionization equilibrium of Fe lines with the programFUNDPAR (Saffe 2011). The C I abundances are determined fromequivalent widths of2 lines (5380.34Å and 5052.17Å) measured with the SPLOT task of IRAF. Our spectrado not include relatively intense N I lines, then we collect NI abundances from literature(Ecuvillon et al. 2004b). There is a good agreement between th C I abundances andliterature (Ecuvillon et al. 2004a) for 26 stars in common (aver ge difference∼0.05dex).Tabla 1. Average and Dispersion of molecular indices for EH and no-EH stars.EH stars no-EH stars(n=38) (n=19)δCH4300±σ 0.08±0.04 0.10±0.05δS3839±σ 0.34±0.24 0.20±0.17The strength of the CN molecular band seem to increase with the abundances of C,N and Fe, as showed in the Figure 2. Then the CN molecule depends on their individual52 C. Saffe et al.Figura 2. IndexδS3839 vs abundances of C I, N I and Fe, respectively. EH andno-EH stars are showed by filled and empty points, respectively.components C and N, and both abundances scales with Fe. If EH stars are metal-rich,then we could expect different distributions for the CN molecul . This could explain,at least in part, the dissimilar distributions of CN presented in the Figure 1 and Table1. The dependence between the molecular intensity and abundnce of their elements isexpected in the case of molecular equilibrium. We caution again that these results arebased on relatively small samples.6. SummaryWe measured the strength of the CN and CH molecular bands in a sample of EH andno-EH stars. The indexδS3839 seem to present a different distribution for EH and no-EH stars. The difference in the distributions could be explained, at least in part, withthe fact that the strength of the CN molecule scales with Fe (EH stars are metal-rich).We expect to increase the number of stars to verify the tendences observed in this work.ReferenciasBond, J. C., Lauretta, D. S., Tinney, C. G., et al., 2008, ApJ 682, 1234Bond, J. C., Tinney, C. G., Butler, R., et al., 2006, MNRAS 370, 163Ecuvillon, A., Israelian, G., Santos, N., et al., 2004, A&A 418, 703Ecuvillon, A., Israelian, G., Santos, N., et al., 2004, A&A 426, 619Fischer, D. A., Valenti, J., 2005, ApJ 622, 1102Gilli, G., Israelian, G., Ecuvillon, A., et al., 2006, A&A 449, 723Harbeck, D., Smith, G. H., Grebel, E. K., 2003, AJ 125, 197Santos, N. C., Israelian, G., & Mayor, M. 2004, A&A, 415, 1153Pancino, E., Rejkuba, M., Zoccali, M., et al., 2010, A&A 524,4Saffe, C., 2011, RevMexAA 47,3van Dishoeck, E., 2009, Astrophysics in the Next Decade, Astrophysics and Space ScienceProc., Springer Netherlands, p. 187

CN and CH bands in Exoplanet Host Stars

CONICET Digital

Asociación Argentina de AstronomíaBAAA, Vol. 54, 2011J.J. Clariá, P. Benaglia, R. Barbá, A.E. Piatti & F.A. Bareilles, eds.PRESENTACIÓN MURALCN and CH bands in exoplanet host starsC. Saffe1, E. Jofré1 & R. Petrucci1(1) Instituto de Cs. Astronómicas, de la Tierra y del Espacio (ICATE)Abstract. We measured the strength of CN and CH molecular bands in a sam-ple of stars with and without exoplanets (indices δS3839, δS4142 and δCH4300).The index δS3839 seem to present smaller values for stars without exoplanets.No correlation is found between molecular bands and exoplanet parameters,supporting the primordial hypothesis of planet formation. The CN band strengthseem to increase with C, N and Fe abundances. This could explain at least inpart the dissimilar distributions of CN observed for stars with and without exo-planets. We caution that this is an initial result based in relatively small numberof objects.Resumen. En este trabajo medimos la intensidad de las bandas molecularesCN y CH en una muestra de estrellas con y sin exoplanetas (indices δS3839,δS4142 y δCH4300). El índice δS3839 parece ser menor en estrellas sin exopla-netas. El hecho de que la banda CN aumente con la metalicidad, puede explicaral menos en parte las diferentes distribuciones observadas en estrellas con y sinexoplanetas. Advertimos que hasta el momento las muestras son relativamentepequeñas.1. IntroductionMain-sequence exoplanet host (EH) stars are, on average, metal-rich in comparison tono-EH stars (e.g. Santos et al. 2004). Fischer & Valenti (2005) showed that the probabi-lity to present an exoplanet increase with the metallicity of the star. On the other hand,the molecular content in the atmospheres of EH stars does not received the same atten-tion in literature. In particular, molecular bands of CN and CH are readily observed inthe spectra of solar-type stars.Different molecules are commonly detected in protoplanetary disks, such as brightlines of CO and HCO+. Also lines of DCO+, CN, HCN, CCH and other molecularspecies are observed (see e.g. the review of van Dishoeck 2009). Different works showsthat molecules are present in protoplanetary disks and could be important ingredientsin the planet formation.Then, the aim of this work is to directly compare (to our knowledge, for the firsttime) the molecular strengths in the atmospheres of stars with and without low-masscompanions or exoplanets. This study will help to determine if the strength of certainmolecular bands observed in main-sequence stars could play a role in the planet for-mation process. Also we search for possible correlations between the molecular indicesand exoplanet parameters (semi-major axis a, eccentricity e and planet mass m seni).4950 C. Saffe et al.This comparison allow us to support the primordial scenario of planet formation, fo-llow a reasoning similar to Bond et al. (2006). In this scenario the abundance content ofthe star is similar to their original parent cloud. However, we caution that the accretionhypothesis (i.e. the increase of abundances due to external pollution of material) couldnot be totally excluded.2. Observational materialWe observed 38 southern EH stars from the California and Carnegie and the GenevaObservatory planet search lists1. The 38 stars we observed have V magnitude between1.5 and 8.9 and spectral types FGK (5, 26 and 7 objects, respectively), as specified inthe Hipparcos database. We also observed a sample of 19 stars not known to have anyplanetary-mass companions (Santos et al. 2004, Bond et al. 2008, Gilli et al. 2006). The19 stars we observed have V magnitude between 2.8 and 8.3 and spectral types FGK (2,11 and 6 objects, respectively). The stars studied in this work do not present IR excessindicative of circumstellar dust.The spectra were obtained at Complejo Astrónomico El Leoncito (CASLEO) bet-ween April 21 and 25, 2008 and October 10 and 15, 2010. We used the 2.15 m telescopeequipped with a REOSC echelle spectrograph and a TEK 1024x1024 CCD detector. Wehave used a grating with 400 lines mm−1. The spectra cover a range 3500-6500 Å andthe S/N ratio is ∼150. The data were reduced using IRAF procedures and the sbandstask was used to measure the strength of the molecular bands.3. Spectral indicesWe measure the strength of 2 CN bands at ∼3883 Å, ∼4215 Å and a CH band at ∼4300Å using the spectral indices S3839, S4142 and CH4300 defined in literature (e.g. Har-beck et al. 2003). The index definitions are:S3839 = -2.5 log F3861−3884F3894−3910,S4142 = -2.5 log F4120−42160.5F4055−4080+0.5F4240−4280,CH4300 = -2.5 log F4285−43150.5F4240−4280+0.5F4390−4460,where F3861−3884, for instance, is the summed spectral flux in ADU counts from 3861to 3884 Å. To determine the uncertainty, we assumed pure photon noise statistics andadded the dispersion of the indices derived from individual spectra. The average dis-persions are 0.151, 0.098 and 0.064 for S3839, S4142 and CH4300, respectively. Weapplied a temperature and gravity correction similar to Harbeck et al. (2003) and refe-rred the corrected indices to as δS3819, δS4142 and δCH4300.There is a general agreement between the δS3839 and δS4142 values, howeverS4142 is less sensitive to the intensity of the CN molecule (Harbeck et al. 2003, Pancinoet al. 2010). Then, we adopt the index S3839 to measure the strength of the CN band,similar to these literature works.1http://exoplanets.org, http://obswww.unige.ch/exoplanetsCN and CH bands in exoplanet host stars 51Figura 1. Distribution of the indices δCH4300 and δS3839. EH and no-EH starsare showed by filled and empty histograms, respectively.4. Molecular bands in EH and no-EH starsWe present in the Figure 1 the distribution of the indices δCH4300 and δS3839. EHand no-EH stars are showed by filled and empty histograms, respectively. In the Ta-ble 1 we present the average and dispersion of the indices. The Figure 1 and the Table1 shows that the distribution of δCH4300 values for EH and no-EH stars are simi-lar. However, for δS3839 no-EH stars seem to concentrate in relatively smaller values(δS3839<∼0.6). The difference is also present in the values of Table 1. A Kolmogorov-Smirnov test gives a probability of %20 that both distributions represent the same po-pulation. We caution that this is an initial result and more stars are needed to verify asignificative difference.No clear relation is apparent between molecular indices and exoplanet parameters(a, e and m seni), which is naturally explained by the primordial scenario of planetformation (e.g. Bond et al. 2006). However, the accretion hypothesis could not be totallyexcluded.5. Carbon abundances from atomic linesThe stellar parameters Teff , log g, [Fe/H] and ξ (microturbulence velocity) have beenderived by requiring excitation and ionization equilibrium of Fe lines with the programFUNDPAR (Saffe 2011). The C I abundances are determined from equivalent widths of2 lines (5380.34 Å and 5052.17 Å) measured with the SPLOT task of IRAF. Our spectrado not include relatively intense N I lines, then we collect N I abundances from literature(Ecuvillon et al. 2004b). There is a good agreement between the C I abundances andliterature (Ecuvillon et al. 2004a) for 26 stars in common (average difference ∼0.05dex).Tabla 1. Average and Dispersion of molecular indices for EH and no-EH stars.EH stars no-EH stars(n=38) (n=19)δCH4300 ±σ 0.08±0.04 0.10±0.05δS3839 ±σ 0.34±0.24 0.20±0.17The strength of the CN molecular band seem to increase with the abundances of C,N and Fe, as showed in the Figure 2. Then the CN molecule depends on their individual52 C. Saffe et al.Figura 2. Index δS3839 vs abundances of C I, N I and Fe, respectively. EH andno-EH stars are showed by filled and empty points, respectively.components C and N, and both abundances scales with Fe. If EH stars are metal-rich,then we could expect different distributions for the CN molecule. This could explain,at least in part, the dissimilar distributions of CN presented in the Figure 1 and Table1. The dependence between the molecular intensity and abundance of their elements isexpected in the case of molecular equilibrium. We caution again that these results arebased on relatively small samples.6. SummaryWe measured the strength of the CN and CH molecular bands in a sample of EH andno-EH stars. The index δS3839 seem to present a different distribution for EH and no-EH stars. The difference in the distributions could be explained, at least in part, withthe fact that the strength of the CN molecule scales with Fe (EH stars are metal-rich).We expect to increase the number of stars to verify the tendences observed in this work.ReferenciasBond, J. C., Lauretta, D. S., Tinney, C. G., et al., 2008, ApJ 682, 1234Bond, J. C., Tinney, C. G., Butler, R., et al., 2006, MNRAS 370, 163Ecuvillon, A., Israelian, G., Santos, N., et al., 2004, A&A 418, 703Ecuvillon, A., Israelian, G., Santos, N., et al., 2004, A&A 426, 619Fischer, D. A., Valenti, J., 2005, ApJ 622, 1102Gilli, G., Israelian, G., Ecuvillon, A., et al., 2006, A&A 449, 723Harbeck, D., Smith, G. H., Grebel, E. K., 2003, AJ 125, 197Santos, N. C., Israelian, G., & Mayor, M. 2004, A&A, 415, 1153Pancino, E., Rejkuba, M., Zoccali, M., et al., 2010, A&A 524, 44Saffe, C., 2011, RevMexAA 47,3van Dishoeck, E., 2009, Astrophysics in the Next Decade, Astrophysics and Space ScienceProc., Springer Netherlands, p. 187

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CN and CH bands in Exoplanet Host Stars

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