$\delta$ Eri is a K-type subgiant with solar metallicity.
\citet{2005A&A...436..253T} determined the limb-darkened angular diameter of $\delta$ Eri from VLTI/VINCI interferometry to be $\Theta=2.39\pm0.03$~mas.
Together with the bolometric flux, $F_{\rm bol}$, the angular diameter can be used to derive a fundamental value for the effective temperature.
$F_{\rm bol}$ can be determined in two ways -- either from the $V$ magnitude and the bolometric correction BC$_{\rm V}$, or from an integration over spectrophotometry and narrow- or broadband photometry covering the whole wavelength range in which the stellar flux is emitted.
For the former approach, the calibration of \citet{1999A&AS..140..261A} gives BC$_{\rm V} = -0.24\pm0.05$ for $\delta$ Eri, which results in $F_{\rm bol} = 1.26\cdot10^{-9}$~W~m$^{-2}$ with an error of 5\%. This gives \Teff = $5070\pm70$~K, where the error in \Teff\ is obtained by propagating the errors in $BC_{\rm V}$ and $\Theta$.

In a second approach, we estimated $F_{\rm bol}$ from the spectrophotometry by \citet{1997yCat.3201....0A} in the range 320 to 735~nm, supplemented in the IR by the four red-most bands of the 13-color photometry by \citet{1975RMxAA...1..299J} and the three 2MASS \citep{2006AJ....131.1163S} bands (J, H, K$_s$) with the absolute flux calibration by \citet{2003AJ....126.1090C}.
The integration over these data gives $F_{\rm bol} = 1.04^{+0.2}_{-0.1}\cdot10^{-9}$~W~m$^{-2}$, which corresponds to \Teff = $4840^{+230}_{-120}$~K. The bolometric flux may be underestimated by as much as 20\% due to unknown photometry outside the observed wavelength range. On the other hand, $F_{\rm bol}$ may be overestimated due to spectral features not being represented correctly by the observed photometry. Thus, the more direct approach turns out to give a less accurate temperature estimation.

Table~\ref{tab:para} summarizes these \Teff\ values together with a compilation of atmospheric parameters found in the literature after the year 2000\footnote{see the PASTEL database at \texttt{http://pastel.obs.u-bordeaux1.fr/}}, including also metallicity \met\ and microturbulence $\xi$.
In Section~\ref{ana}, we carry out a spectroscopic analysis with our own data and models, using the following starting values for the stellar parameters: \Teff=5070~K, \logg=3.78, $\xi$=1.08~kms$^{-1}$.

\begin{table*}[h]
   \caption{Compilation of atmospheric parameters for $\delta$ Eri found in the literature. The column labelled ``Method for \Teff, \logg'' indicates the methods for \Teff\ and \logg\ determination used by the authors. \emph{Spectroscopy} refers to excitation and ionization equilibrium for \Teff\ and \logg, respectively, in a spectroscopic analysis of high-resolution spectra. \emph{IRFM} refers to the infrared flux method %\citep{1977MNRAS.180..177B}.
\emph{Parallax} means a gravity determination using the Hipparcos parallax, \Teff~ and a mass estimate from stellar isochrones.}
\label{tab:para}
\centering
\begin{tabular}{l l l l l p{39ex}}
\hline\hline
\Teff\ [K] & \logg\ [cgs] & \met & $\xi$ [km s$^{-1}$] & Reference & Method for \Teff; \logg \\
\hline
$5070\pm70$          & & & & this paper & $\Theta$+$F_{\rm bol}$ from $BC_{\rm V}$ \\
$4840^{+230}_{-120}$ & & & & this paper & $\Theta$+$F_{\rm bol}$ from spectrophotometry \\
5020 $\pm$  70 & 3.73 $\pm$ 0.1  & 0.24 $\pm$ 0.14 & 0.80 & Bensby et al.            (2003) & spectroscopy; parallax \\
5023 $\pm$ 419 & 4.14 $\pm$ 0.18 & 0.18 $\pm$ 0.07 & 1.04 & Allende Prieto et al.    (2004) & IRFM; parallax \\
5074 $\pm$  60 & 3.77 $\pm$ 0.16 & 0.13 $\pm$ 0.08 & 1.08 $\pm$ 0.06 & Santos et al. (2004) & both spectroscopy \\
5140 $\pm$ 105 & 4.10 $\pm$ 0.26 & 0.05 $\pm$ 0.13 & 1.32 $\pm$ 0.18 & Affer et al.  (2005) & both spectroscopy (their ``Method 1'') \\
5100 $\pm$ 100 & 3.8  $\pm$ 0.10  & 0.18 $\pm$ 0.09 & 0.60 & Luck \& Heiter           (2005) & both spectroscopy \\
5095 $\pm$  44 & 3.98 $\pm$ 0.06 & 0.16 $\pm$ 0.03 & 0.85 & Valenti \& Fischer       (2005) & synthetic spectrum fit \\
5008           & 3.78 $\pm$ 0.05 & 0.21 $\pm$ 0.11 & 0.88 & Ram\'irez et al.         (2007) & IRFM; parallax \\
5044 $\pm$  80 & 3.84 $\pm$ 0.10  & 0.12 $\pm$ 0.07 & 0.92 $\pm$ 0.20 & Fuhrmann      (2008) & spectroscopy (Balmer line wings; and  Mg Ib line wings) \\
5150 $\pm$  51 & 3.89 $\pm$ 0.08 & 0.13 $\pm$ 0.04 & 1.01 $\pm$ 0.06 & Sousa et al.  (2008) & both spectroscopy (extended line list compared to Santos et al. 2004) \\
\hline
\end{tabular}
\end{table*}
% cite doesn't work in tables, have to add citations manually
\nocite{2003A&A...410..527B}
\nocite{2004A&A...420..183A}
\nocite{2004A&A...415.1153S}
\nocite{2005A&A...433..647A}
\nocite{2005AJ....129.1063L}
\nocite{2005ApJS..159..141V}
\nocite{2007A&A...465..271R}
\nocite{2008MNRAS.384..173F}
\nocite{2008A&A...487..373S}
