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Effective Temperature, Surface Gravity and Metallicity for Classical Cepheids and RR Lyraes (Luck and Andrievsky 2004; Kovtyukh Et Al

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Effective Temperature, Surface Gravity and Metallicity for Classical Cepheids and RR Lyraes (Luck and Andrievsky 2004; Kovtyukh Et Al Testing iSpec for the determination of atmospheric parameters and abundances of delta Cephei and RR Lyrae Sergi Blanco-Cuaresma1 , Richard I Anderson!, Laurent Eyer1, #ami Mowla&i1 ¹ Observatoire de Genève, Université de Genève, CH-1290 Versoix, Switzerland. " #$%sics and Astrono(% Department, The ,ohns Ho*-ins University, 3400 0. Charles St, Baltimore, US' Abstract C assical Cep$eids and 22 3%raes are radial y *4 sating stars where the spectral ty*e varies depending on t$eir *$ase (Ce*$eids: F-type at maxim4(, G-K type at mini(4(; 22 3yraes: A or F-types). Several studies used synthesis and t$e e<4ivalent widt$ (ethod to deter(ine the evo 4tion of e>ective te(perature, surface 5ravity and metal icity for & assical ce*$eids and 22 3yraes 634&- and 'ndrievsk% 2004: Kovtyuk$ et al! 2005: Andrievs-% et al 2005; 34&- et al 200@: +a-eda et al. 2013; Fossati et al! 2014)! We evaluate t$e app icability of iSpec 61 anco-Cuaresma et al! 2014), which $as been extensivel% 4sed with non-pu sating FGK stars, and derive atmospheric parameters as a =4nction of *$ase for δ Cephei and RRLyrae (the two prototypes stars for eac$ c ass;! Ingredients. H'2CS (odel atmos*$eres 6G4sta=sson et a . 200@;, so ar abundances =ro( Grevesse et a . $ethod 6200J), VAL) ato(i& line list and SPEC+2UM code for synt$eti& s*ectra generation (Gray & Corba y, 199/;! Kffective te(*erature Sur=a&e gravit% Meta i&it% Fig 1. At(osp$eric *ara(eters derived by iSpec (in4s t$e reference va 4es (Y-axis) =or t$e Gaia FG9 Ben&$(ark Stars. 2esu ts are sorted b% effective tem*erat4re, surface gravit% and (eta i&it%, respective y, and reference val4es are shown in t$e P-axis. Co or &ode represent t$e referen&e meta icity (b 4e bein5 metal poor and red corresponds to meta rich;! On t$e 4**er part, t$e median difference and dispersion is indicated! Cr II )e I Cr I iSpec[1] is an o*en so4rce spectrosco*ic =ramework that i(*le(ents ro4tines =or spectral treat(ent and the deter(ination o= at(ospheric *ara(eters D &$e(ical ab4ndances b% 4sing the spectral fitting techni<4e 1!0 6Blan&o-C4aresma et a ! 2014). Given a se ection o= spectral re5ions and absor*tion lines, iS*ec co(*4tes synthetic spectra on-the-F% and (ini(izes the di>erences with the observed spe&tra =ollowing a 3evenber5GHar<4ardt (least sq4ares; algorit$(! 0!9 x 4 F 0!@ (aia )(K Benchmar+ +he selection o= absor*tion ines is o*ti(ized and &alibrated to re*rod4ce the d e z i Stars re=eren&e values 6Heiter et al. 2015, ,o=ré et a ! 2014, Jo=ré et al. 2015 and Hawkins et al. 2016; as a ( r 0!J shown in Fi5.1, whi&h is also 4se=4l to better esti(ate t%*ical errors =or ea&h *arameter and red4&e o ,hase / 34 &orrelations. +his gro4* o= ver% well-known stars have re=erence *arameters derived inde*endent % =ro( 0 ,hase / 02 spectrosco*% and it does not contain any *4lsatin5 star. 0!I ,hase / 1! +o eval4ate iS*ec with *4lsating stars, we analyzed 176 spectra o= ' Cephei and 136 o= RRLyrae 0!? ,hase / /0 observed with the HE2HKS spectro5raph 6reso 4tion ~ 85,000) installed on the Fle(ish Mercator te esco*e at la Palma 6Observatorio 2o<4e de los H4&ha&hos)! 's shown in Fi5. 2, the spe&tra have strong ?24.65 524!J0 524!J? 52/!@0 variations over the who e *4lsating &%cle and the line sele&tion based on the Gaia FG9 Ben&$(ark stars Aavelen5t$ (n(; (i5ht not be the best for t$is kind o= stars. Fig 2. Absorption ines =ro( observed spe&tra correspondin5 to different *$ases o= t$e [1] htt*://www!blan&o&4ares(a!co(/s/ *4 satin5 c%& e =or δ Cephei! Preliminary results and future work +raditionally, fro( the three main at(ospheric para(eters, the most diQ&4lt to derive =ro( stellar spe&tra is the surface gra&ity 6i!e. lo565;; be&ause its e>ects are (ore subtle than the e>e&ts o= the e>ective te(*erat4re or the (etalli&it%. In Fi5. 3, we can &lear % observe these diQ&4lties: when we a**ly a non-adapted traditional spe&trosco*ic (ethod to *4lsatin5 stars, derived 5ravities do not see( to =ollow a *$%sically lo5i&al evo 4tion. 0evertheless, (etallicit% is 5 oba % stab e 6-0.09±0.03 dex; and e-ective temperature is beauti=4 % re*rod4&ed with (ini(4( close to the (axi(4( contra&tion and (axi(4( at =astest ex*ansion. 2an5es and avera5e results agree with Andrievsky et al. 2005. In ter(s o= broadening parameters, (a&rot4rb4len&e velocit% 6V(ac) and *rojected rotation 6V sin6i;; are very diQ&4lt to disentangle even i= their *roE es are not exact % the sa(e! Fig .! 2adia velocity as reported b% Anderson et a ! (2015) and at(os*$eric *ara(eters derived b% iS*ec =or ' Cephei. 2esu ts are fo ded in *$ase considerin5 a period o= 5.366.I7120 da%s and t$e epo&$ o= (axi(4( ight o= 24???06!JI28! Individ4al chemical abundances in =4n&tion o= *hase 6Fi5! /; are stable as it was ex*e&ted (the che(ica &o(*osition o= the star sho4ld not var%;. We plan to use this in=or(ation to identi=% absor*tion lines that are reliab e and stable 6less affected by t4rb4lence; d4rin5 the whole *4lsating &%cle. +$is new line selection will he * to i(*rove t$e determination o= at(ospheric *ara(eters and it will allow 4s to be (ore conEdent in the st4d% o= other less known Ce*heids and R2 3yrae! RRLyrae. 2esults are si(ilar to ' Cephei altho4gh (etalli&it% is less stable over the *4lsating &%&le. 223%rae is a (etal-*oor star 6~ -1.45 dex; that co(*li&ates even Fig 4. )i>erentia &$emica ab4ndances re ative to a δ Cephei s*ectra. Silicon, Calciu( and Titaniu( are a *$a (ore its ana %sis elements, w$ile C$ro(iu(, Iron and Ni&-el are iron *ea- elements.! Sergi Blanco-Cuaresma Ser5i.B anco@unige!&$ http://ww%.blancocuaresma.com/s5.
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