Wavelength calibration of the Hamilton echelle spectrograph

TL;DR

This paper details the wavelength calibration process for the Hamilton echelle spectrograph at Lick Observatory, utilizing titanium lines due to the absence of thorium lines in the lamp spectrum, achieving high calibration accuracy.

Contribution

It introduces a new titanium line list for calibration and demonstrates a method to calibrate without thorium lines, improving spectrograph calibration accuracy.

Findings

Calibration accuracy of about 0.006 Å achieved.

Identification of titanium lines as effective calibration references.

Method applicable to spectrographs lacking thorium lines.

Abstract

We present the wavelength calibration of the Hamilton echelle spectrograph (the Lick observatory). The main problem of the calibration arises from the fact that thorium lines are absent in the spectrum of "ThAr" hollow-cathode lamp now under the operation. On the other hand, numerous unknown strong lines are present in the spectrum. These lines was identified with titanium. We estimate the temperature of the lamp gas which permits us to calculate the intensities of the lines, and to select a large number of relevant Ti I and Ti II lines. The titanium line list for the Lick hallow-cathode lamp is presented. The wavelength calibration using this line list was made with accuracy about 0.006A.