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rs  ophiuchi is a recurrent nova that has undergone nova eruptions in 1898 , 1933 , 1958 , 1967 , 1985 , and possibly @xcite 1907 . as in the case of a classical nova
, the eruption follows a thermonuclear runaway on the surface of the white dwarf @xcite .
the key differences between classical and recurrent novae , in terms of both system properties and outburst behaviour , are reviewed by anupama .
the recurrents are a heterogeneous class of objects but the rs  oph  type is characterized by a semi - detached binary consisting of a roche - lobe - filling m  giant mass donor ( m8iii in the case of rs  oph ; @xcite ) and a massive ( close to the chandrasekhar limit ) white dwarf ( _ classical _ novae almost exclusively have cool _ dwarf _ mass donors ) .
[ cols="^,^,^,^,^,^,^,^,^,^ " , ]     [ coronal ]
the spectra have been dereddened for @xmath2 @xcite and the dereddened fluxes are reported in table  [ nebular ] for the he and o lines and in table  [ coronal ] for the coronal lines .
assuming that the continuum that is clearly visible in fig .
[ data ] is optically thin free - free and free - bound emission , we estimate the electron temperature to be @xmath0  k for all three of our observations , but note that the flux calibration for the march observation is not reliable as the data were taken through cloud . this temperature is constrained primarily by the magnitude of the brackett and pfund discontinuities at 1.45  and 2.28  respectively ( fig .
[ cont ] ) .
the electron temperature derived from the optically thin emission is considerably less than that implied by the presence of ir coronal lines in the spectra ( see below ) , or inferred from radio @xcite and x - ray @xcite observations .
there remains an excess at wavelengths @xmath3 , some ( but not all ) of which may be due to a contribution from the shocked gas .
using flux ratios for the hydrogen recombination lines , and assuming case  b @xcite , we find that the electron density for day  55.71 is @xmath4  @xmath5 .
assuming the mass - loss value given by obrien et al .
, wind velocity 20  and shock velocity @xmath6  ( cf . fig .  [ vel_fwzi ] ) , the corresponding wind column , integrated from the base of the unshocked wind to infinity , is @xmath7  @xmath8 , in good agreement with that obtained from the x - ray data ( e.g. fig .  3 of bode et al .
we can use the dereddened fluxes of the silicon coronal lines for 2006 april 9 to estimate the temperature in the coronal region .
the relative fluxes for lines in a coronal gas are discussed by greenhouse et al .
and we follow their analysis here , using collisional strengths from osterbrock and blaha , and ionization fractions as a function of temperature from shull & van steenberg .
we find that the temperature of the coronal gas is @xmath9  k ( @xmath10  kev ) .
we note that ness et al .
deduced a temperature of a few @xmath11  k from the coronal x - ray lines in a chandra observation on jun 4.5 ; the temperature for the coronal gas obtained here is broadly consistent with the x - ray data .
the deduced electron temperature , @xmath0  k , implies that the hydrogen ir emission on all three dates is primarily due to emission by the red giant wind , ionized by the ultraviolet flash when rs  oph  erupted .
emission by the shocked wind must also contribute to the total emission ; however ir observational evidence for this is apparent only on day 55.71 with the clear development of the s and si coronal lines . as the shock propagates into , and eventually breaks out of , the wind ( which is predicted to occur around @xmath12  days ; see obrien , bode & kahn 1992 ) we expect that the contribution of the coronal gas will become dominant , and that of the cooler gas to decline and eventually disappear .
while there exist at least two regions with greatly differing temperatures in the environment of rs  oph  the determination of abundances is problematic .
however we anticipate that this will change when the shock breaks out of the giant wind .
this next phase will be discussed in a forthcoming paper .
( 5.0,4.5 ) ( 0.0,4.0 )
we have reported the early ir spectroscopy of the 2006 eruption of the recurrent nova rs  oph , covering the first 55  days .
we find a spectrum dominated by hydrogen recombination lines arising from a gas at @xmath0  k ; silicon coronal lines prominent on day  55 , implying a temperature for the coronal gas of 930000  k.    ir ( and other ) observations of this remarkable object are continuing and in subsequent papers we will present contemporaneous observations carried out with ukirt and the spitzer space observatory .
we thank the ukirt director and the various ukirt observers for supporting this project .
the united kingdom infrared telescope is operated by the joint astronomy centre on behalf of the u.k .
particle physics and astronomy research council ( pparc ) .
trg is supported by the gemini observatory , which is operated by the association of universities for research in astronomy , inc .
, on behalf of the international gemini partnership of argentina , australia , brazil , canada , chile , the united kingdom , and the united states of america .
use of the ukirt by ym and yt is supported by national astronomical observatory of japan .
rdg and cew are supported in part by the nsf ( ast02 - 05814 ) . the work of dkl , rjr and rwr is supported by the aerospace corporation s independent research and development program .
n. gratefully acknowledges support provided by nasa through chandra postdoctoral fellowship grant pf5 - 60039 awarded by the chandra x - ray center , which is operated by the smithsonian astrophysical observatory for nasa under contract nas8 - 03060 .
jpo and klp acknowledge support from pparc .
sgs acknowledges partial support from nsf grants to arizona state university .
data reduction was carried out using hardware and software provided by pparc .
starrfield s. , shore , s. n. , kenyon , s. j. , sonneborn , g. , 1996 , in _ cool stars ; stellar systems and the sun 9 _ , asp conference series vol .
109 , p.665 , eds r. pallavicini , a. k. dupree , astronomical society of the pacific , san francisco
we present infrared spectroscopy of the recurrent nova rs  ophiuchi , obtained 11.81 , 20.75 and 55.71  days following its 2006 eruption . 
 the spectra are dominated by hydrogen recombination lines , together with he , o and o lines ; the electron temperature of @xmath0k implied by the recombination spectrum suggests that we are seeing primarily the wind of the red giant , ionized by the ultraviolet flash when rs  oph  erupted 
 . however , strong coronal emission lines ( i.e. emission from fine structure transitions in ions having high ionization potential ) are present in the last spectrum . 
 these imply a temperature of @xmath1  k for the coronal gas ; this is in line with x - ray observations of the 2006 eruption . the emission line widths decrease with time in a way that is consistent with the shock model for the x - ray emission .    
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