Precision wavelength calibration for Radial Velocity measurements using Uranium lines between 3800-6900 AA. (arXiv:2105.12942v2 [astro-ph.IM] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Sharma_R/0/1/0/all/0/1">Rishikesh Sharma</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chakraborty_A/0/1/0/all/0/1">Abhijit Chakraborty</a>

We present here the precise wavelength calibration of a high-resolution
spectrum using Uranium (U) lines in the wavelength range of 3809 – 6833 AA
for precision radial velocity measurements for exoplanet detection or related
astrophysical sciences. We identify 1540 well-resolved U lines from a
high-resolution (R=67,000) spectrum of the uranium-argon hollow cathode lamp
(UAr HCL) using PARAS spectrograph in the aforesaid wavelength range. We
calculate the neutral and first allowed transitions (Ritz wavelength) of U from
its known energy levels and compare them with our observed central wavelengths.
We measure an offset of -0.15 mAAspace in our final U line list. The line
list has an average measurement uncertainty of 15 m s$^{-1}$ (0.013 pixels or
0.28 mAA). We included these lines to the PARAS data analysis framework to
perform the wavelength calibration and then calculate the multi-order Radial
Velocity (RV) of PARAS spectra. The typical dispersion of residuals around the
wavelength solution of a UAr spectrum, using U lines, is found to be 0.8
mAAspace($sim$45 m s$^{-1}$). With the use of this line list, we present our
results for the precision RV of an on-sky source (A RV standard star), and an
off-sky source (A HCL) observed with PARAS along with UAr HCL. We measure the
dispersion in absolute drift difference between two fibers (inter-fiber drift)
for a span of 6.5 hours to be 88 cm s$^{-1}$, and the RV dispersion
(${sigma_{RV}}$) for a RV standard star, HD55575 over the course of $sim$450
days to be 3.2 m s$^{-1}$. These results are in good agreement with the
previous ones measured using the ThAr HCL. It proves that the ThAr HCL with
$sim$ 99% pure-Th are replaceable with the UAr HCL for the wavelength
calibration of the high-resolution spectrographs such as PARAS (R $leq$
67,000) to achieve a RV precision of 1-3 m s$^{-1}$ in the visible region.

We present here the precise wavelength calibration of a high-resolution
spectrum using Uranium (U) lines in the wavelength range of 3809 – 6833 AA
for precision radial velocity measurements for exoplanet detection or related
astrophysical sciences. We identify 1540 well-resolved U lines from a
high-resolution (R=67,000) spectrum of the uranium-argon hollow cathode lamp
(UAr HCL) using PARAS spectrograph in the aforesaid wavelength range. We
calculate the neutral and first allowed transitions (Ritz wavelength) of U from
its known energy levels and compare them with our observed central wavelengths.
We measure an offset of -0.15 mAAspace in our final U line list. The line
list has an average measurement uncertainty of 15 m s$^{-1}$ (0.013 pixels or
0.28 mAA). We included these lines to the PARAS data analysis framework to
perform the wavelength calibration and then calculate the multi-order Radial
Velocity (RV) of PARAS spectra. The typical dispersion of residuals around the
wavelength solution of a UAr spectrum, using U lines, is found to be 0.8
mAAspace($sim$45 m s$^{-1}$). With the use of this line list, we present our
results for the precision RV of an on-sky source (A RV standard star), and an
off-sky source (A HCL) observed with PARAS along with UAr HCL. We measure the
dispersion in absolute drift difference between two fibers (inter-fiber drift)
for a span of 6.5 hours to be 88 cm s$^{-1}$, and the RV dispersion
(${sigma_{RV}}$) for a RV standard star, HD55575 over the course of $sim$450
days to be 3.2 m s$^{-1}$. These results are in good agreement with the
previous ones measured using the ThAr HCL. It proves that the ThAr HCL with
$sim$ 99% pure-Th are replaceable with the UAr HCL for the wavelength
calibration of the high-resolution spectrographs such as PARAS (R $leq$
67,000) to achieve a RV precision of 1-3 m s$^{-1}$ in the visible region.

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