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classical and recurrent novae  distinguished by the observation of one or more eruptive events ,
respectively  are thermonuclear runaways ( tnr ) on the surface of a white dwarf ( wd ) star which ensues following extensive accretion of hydrogen rich material from a less evolved secondary star .
the ejected material is rich in heavy elements which enrich the interstellar medium ( @xcite , see also gehrz et al . , these proceedings ) .
the nova eruptions are the most common thermonuclear runaways in the galaxy ( 34@xmath0 novae per year ; @xcite ) and scale with galaxy size ( @xcite ) .
the infrared temporal evolution of the nova is nicely described in gehrz et al .
( these proceedings ) and for detailed reviews on interefometric observations of novae , see chesneau & banerjee ( 2012 ) and chesneau ( 2014 ) . of particular interest , to this work , is that during the initial phases of the eruption the ejected material can be modelled as an optically thick fireball that radiates like a blackbody and as the expansion continues and reduces in density , the infrared continuum becomes dominated by optically thin free - free emission with strong hydrogen re - combination lines on top .
observations of novae are going through a renaissance over the last decade or so driven by the upgrade of telescopes , instruments , and new discoveries ( see the various contributions in @xcite ) .
of particular note , the discovery of high energy @xmath1-ray emission ( @xcite ) and pinpointing the location of @xmath1-ray production , from internal shocks due to different velocity components at the equatorial and polar regions ( @xcite ) .    a number of factors are required to be systematically studied across the electromagnetic spectrum in order to understand the evolution of the nova eruption . of paramount importance , in any field of astrophysics , is the distance to an object . in the milky way ,
the distance to novae allow us to derive their spatial distribution in order to understand from which population / s novae arise from 
disc / bulge  and also the occurrence of novae in our galaxy .
the first observations with an infrared interferometer occurred with nova v1974  cygni ( 1992 ) on the mk iii interferometer ( @xcite ) . the nova was resolved aroudn 10 days after maximum light . fitting a uniform disk model to the data the distance was estimated to be 2.5 kpc , in line with other studies ( @xcite ) .
there was one more nova - like eruptive event , in v838 mon ( @xcite ) , that was followed with palomar testbed interferometer ( pti ) .
however , this event is largely accepted to have been the merger of two stars .
it was not until the recurrent nova rs ophiuchi erupted in 2006 that infrared interferometric observations truly come to play .
rs oph was observed first with the infrared optical telescope array , keck and pti ( @xcite ) , suggesting that the near - infrared emission arose due to a non - expanding , dense , and ionised circumbinary gaseous disk or reservoir . however , lane et al . ( 2007 ) resolve the emission in rs oph using pti providing clear evidence for a near - infrared source that initially expanded and then began shrieking .
the amber instrument on the very large telescope interferometer ( vlti ) was also used , on day 5.5 after eruption , to measure the @xmath2-band continuum and the br@xmath1 and hei 2.06 @xmath3 m lines ( @xcite ) .
the @xmath2-band emission is dominated by free - free emission and had a smaller size than the br@xmath1 and hei lines ( 3x2 mas , 5x3 mas , and 6x4 mas , respectively ) .
these results were also contrary to monnier et al .
furthermore , chesneau et al . ( 2007 ) found two velocity fields in the br@xmath1 line ; a slowly expanding ring - like structure ( @xmath4  1800  km  s@xmath5 ) , and a fast structure extended in the e - w direction ( @xmath6  25003000  km  s@xmath5 ) .
a two velocity component was also required to replicate the hubble space telescope narrow band imaging observations of the resolved remnant , at day 155 after eruption , and the ground - based optical spectroscopy ( @xcite ) .
lastly , rs oph observations with the keck interferometer nuller , around day 3.8 after eruption , showed evidence for dust that is present in - between eruptions , rather than created during the eruption ( @xcite ) in line with findings from the spitzer space telescope of silicate dust that survives the hard radiation impulse and shock blast wave from the eruption ( @xcite ) .
other novae have been observed since rs oph with infrared interferometric instruments ; the recurrent nova t  pyxidis ( @xcite ) , the dust forming nova v1280 sco ( @xcite ) , and the @xmath1-ray detected classical nova v339 delphini ( 2013 ; @xcite ) .
what is clear from the various bodies of work is that the nova eruption is far from spherical , or uniform disks .
efforts are now under way to understand the progress of the nova eruption from optical to radio observations applying one single model . for example , optical emission line profile fitting of the classical nova v959  mon proved useful in determining , the ejection morphology , inclination angle and the expansion velocity of the ejecta ( @xcite ) . these results are also corroborated with the observations of eclipses at x - ray and optical wavelengths ( @xcite ) and observations of a bipolar ejection morphology at radio frequencies ( @xcite ) .
lastly , applying the free - free thermal process to the models derived at optical wavelengths above we were able to derive the distance to v959  mon ( @xcite ) .    up to now the observations
have provided important information on the distances to these objects assuming uniform / gaussian fitting to the visibilities / images when available as well as departure from these morphologies for the ejecta .
in fact , the distance may also be constrained assuming the blackbody angular radius and doppler expansion velocity which give day of the eruption , the distance and the outburst luminosity ( @xcite and gerzh et al .
these proceedings )
. however , we can extract further information if we assume a thermal free - free emission .
here we will , also , be able to extract ejected masses , temperature of the ejecta , and density profiles of the ejecta .
ideally , we would want to combine all this information with other wavelengths , such as optical for the doppler expansion velocity , in order to reduce the amount of free parameters and computational time .
although the distance is a very important issue , the gaia satellite will largely solve this in the coming years .
furthermore , a suit of new instruments are to be installed in the vlti which will provide marked improvement , both in resolution and sensitivity ( matisse and gravity ) , over current capabilities .
the author would like to thank bob gehrz for reading and commenting on the manuscript and christiaan brinkerink for useful discussion on interferometric observations .
the author also acknowledges financial support from the radboud excellence initiative .
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* q : lizette guzman : * have you used the expansion velocity in the optical compared to the radio emission ?      * q : jose groh : * i had the impression that your models have less flux at the central regions than observed at later times .
could you comment on the reasons for this behaviour and whether this is significant in the context of your models ?    * a : valrio ribeiro : * the models i showed assumed free - free thermal emission , so as input to the models we have ejection velocity , ejected mass , and temperature .
we did not have time to produce a full set of parameter space in order to find the best fit .
so what you are seeing is that the models with chosen input parameters became optically thin quicker than the observations .
we really need to explore the fuller parameter space .
infrared interferometric observations have a great deal of potential to unravel the nature of the nova eruptions . 
 we suggest that techniques , already in place , to derive the ejection details at optical wavelengths be used with infrared interferometric observations to derive parameters such as the ejected mass in a nova eruption . 
 this is achievable based on modelling the initial phase of the eruption when the infrared light is dominated by the free - free thermal process .