cno abundances in stars with planets
DESCRIPTION
CNO abundances in stars with planetsTRANSCRIPT
Conclusion
Analysis
CNO behaviour in planet-‐harbouring starsL. Suárez-‐Andrés1,2, G. Israelian1,2, J.I. González Hernández1,2, V. Adibekyan3, E. Delgado Mena3, N.C. Santos3,4, S.G. Sousa3,4
1 Ins&tuto de Astro.sica de Canarias, E-‐38205 La Laguna, Tenerife, Spain. 2Dpto. Astro.sica, Universidad de La Laguna (ULL), E-‐38206 La Laguna, Tenerife, Spain.3 Ins&tuto de Astro.sica e Ciência do Espaço, Universidade do Porto (CAUP), Rua das Estrelas, 4150-‐762 Porto, Portugal. 4Departamento de Física e Astronomia,
Faculdade de Ciências da Universidade do Porto, Portugal.
IntroducOon
C, N and O are the most abundant elements (aUer H and He). They are produced in stellar interiors through the CNO cycle.
Thermonuclear producXon path for N is different from that of C and O. While for carbon and oxygen the dominant producXon modes are the α-‐chain reacXon, for nitrogen the dominant producXon mode lies in the re-‐arrangement of nuclei during the CNO cycle. These elements play a crucial role in formaXon of biospheres and life. Thus, it is important to study their abundances in extrasolar planets and in the atmospheres of their host star.
We present results for a chemical abundance analysis for stars with and without planets for nitrogen and carbon using NH and CH molecular bands.
Results
Sample
Nitrogen was studied using high-‐resoluXon spectra observed with UVES@VLT. 90 solar-‐type stars were studied, using the NH molecular band located at 3360Å. 50 of these 90 stars are known to be planet hosts.
Carbon was studied using high-‐resoluXon spectra observed with HARPS. 1111 solar-‐type stars were studied, using the CH band located at 4300Å. 128 of these 1111 stars are planetary systems.
Abundances of both nitrogen and carbon were determined using a standard thermodynamic equilibrium (LTE) analysis with the spectral synthesis code MOOG (Sneden, 1973) and a grid of Kurucz (1993) ATLAS9 atmospheres. All stellar parameters were taken from Santos et al. 2004, Sousa et al. 2011(a,b). Chemical abundances of other elements were taken from Adibekyan et al. 2012 (in both cases) and also from Bodaghee et al. 2003 (for nitrogen). Adopted solar abundances are log∊(N)⊙=8.05 dex and log∊(C)⊙=8.50 dex.
Fig 1. LeU: Observed spectrum (solid) and syntheXc (doYed lined, dashed and dashed-‐doYed) for different values of [C/H]. Right: Same as leU but for another target and in the NH band.
Fig 2. LeU: [X/Fe] versus Teff for both carbon (red and orange dots) and nitrogen (blue and green squares). Filled symbols correspond to stars with planets, while open symbols for single stars. As it can be seen, abundances rise unXl 5000K then moderate their increament. We are invesXgaXng the Teff dependence to correct for those trends. Right: [X/Fe] versus logg for both nitrogen and carbon. As it can be seen, no relaXon is found.
Fig 3. LeU: [X/Fe] versus [Fe/H] for both carbon (red and orange dots) and nitrogen (blue and green squares). As it can be seen, abundance is nearly independent of iron. Right: [X/H] versus [Fe/H] for both nitrogen and carbon. A 1:1 relaXon is found for all samples, nitrogen and carbon, for planet hosts and single stars.
We have searched for peculiar trends between those samples (planet hosts and single stars) by represenXng [X/Fe] abundance raXo as a funcXon of Teff and logg (Fig. 2). There is a small dependence with Teff for both carbon and nitrogen samples, with no difference between stars with and without planets. We are invesXgaXng the Teff dependence to correct for those trends. No relaXon can be found for logg.We also looked for disXnguishable trends between those samples by represenXng [X/Fe] abundance versus [Fe/H] for both samples. Both elements are nearly indepedent of iron and they show a 1:1 relaXon with it. (see Fig. 3). As previously, there is no different behaviour between planet hosts and single stars.
Santos et al. 2004, A&A 415.1153S.Sousa et al. 2011a, A&A 526A.99S
Sousa et al. 2011b, A&A 533A.141SAdibekyan et al. 2012, A&A 545A.32A
Bodaghee et al. 2003, A&A 404.715BEcuvillon et al. 2004, A&A 418..703E
Fig 4. CumulaXve histograms comparing single stars with planet hosts (red, stars with planets less massive than 1.5 MJ; in blue, planets more massive than 1.5 MJ) Performing a Kuiper test we can assume that single stars are similar to small-‐planets hosts (Prob 0.72 for N, 0.98 for C) while single stars and giant-‐planets hosts are not (Prob 0.03 for N, 0.33 for C). For nitrogen the late increase in the cumulaXve histogram of stars with massive planets (Mp sini > 1.5 MJ ) indicates that the average [N/Fe] raXo in those stars is higher than in stars with “small planets” (Mp sini < 1.5 MJ ). This may indicate the need of high abundance of nitrogen to be able to form massive giant planets.
We present nitrogen abundances for 90 solar-‐type stars observed with UVES@VLT using the NH band located at 3360Å. We also obtained carbon abundances for 1111 solar-‐type observed with HARPS using the CH molecular band at 4300Å. We performed a LTE analysis to obtain these N and C abundances and invesXgated their abundance trends. We found indicaXons that the abundance raXos [N/Fe] are on average higher in stars with massive giant planets than in stars with less massive planets, which may suggest the need for high amount of available nitrogen in protoplanetary disc in order to build massive giant planets.