Comparing radial velocities of atmospheric lines with radiosonde measurements

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 10/2011; 420(4). DOI: 10.1111/j.1365-2966.2011.20015.x
Source: arXiv


The precision of radial velocity (RV) measurements depends on the precision
attained on the wavelength calibration. One of the available options is using
atmospheric lines as a natural, freely available wavelength reference. Figueira
et al. (2010) measured the RV of O2 lines using HARPS and showed that the
scatter was only of ~10 m/s over a timescale of 6 yr. Using a simple but
physically motivated empirical model, they demonstrated a precision of 2 m/s,
roughly twice the average photon noise contribution. In this paper we take
advantage of a unique opportunity to confirm the sensitivity of the telluric
absorption lines RV to different atmospheric and observing conditions: by means
of contemporaneous in-situ wind measurements by radiosondes.
The RV model fitting yielded similar results to that of Figueira et al.
(2010), with lower wind magnitude values and varied wind direction. The probes
confirmed the average low wind magnitude and suggested that the average wind
direction is a function of time as well. The two approaches deliver the same
results in what concerns wind magnitude and agree on wind direction when
fitting is done in segments of a couple of hours. Statistical tests show that
the model provides a good description of the data on all timescales, being
always preferable to not fitting any atmospheric variation. The smaller the
timescale on which the fitting can be performed (down to a couple of hours),
the better the description of the real physical parameters. We conclude then
that the two methods deliver compatible results, down to better than 5 m/s and
less than twice the estimated photon noise contribution on O2 lines RV
measurement. However, we cannot rule out that parameters alpha and gamma
(dependence on airmass and zero-point, respectively) have a dependence on time
or exhibit some cross-talk with other parameters (abridged).

Download full-text


Available from: P. Figueira,
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present work done to prepare two new near-infrared calibration sources for use on high-precision astrophysical spectrographs. Uranium-neon is an atomic calibration source, commercially available as a hollow-cathode lamp, with over 10 000 known emission lines between 0.85 and 4 μm. Four gas cells — containing C2H2, H13CN, 12CO, and 13CO, respectively—are available as National Institute of Standards and Technology (nist) Standard Reference Materials (SRMs), and provide narrow absorption lines between 1.5 and 1.65 μm. These calibration sources may prove useful for wavelength-calibrating the future near-infrared high-precision radial-velocity spectrometers, including the Calar Alto high-Resolution search for M dwarfs with Exo-earths with a Near-infrared Echelle Spectrograph (CARMENES),1 the SpectroPolarimetre InfraROUge (SPIRou)∗, and the Habitable-Zone Planet Finder (HPF).2
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; 8446. DOI:10.1117/12.925585 · 0.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Context. KIC 10661783 is an eclipsing binary that shows delta Scuti-like oscillations. More than 60 pulsation frequencies have been detected in its light curve as observed by the Kepler satellite. Aims. We want to determine the fundamental stellar and system parameters of the eclipsing binary as a precondition for asteroseismic modelling of the pulsating component and to establish whether the star is a semi-detached Algol-type system. Methods. We measured the radial velocities of both components from new high-resolution spectra using TODCOR and compute the orbit using PHOEBE. We used the KOREL program to decompose the observed spectra into its components, and analysed the decomposed spectra to determine the atmospheric parameters. For this, we developed a new computer program for the normalisation of the KOREL output spectra. Fundamental stellar parameters are determined by combining the spectroscopic results with those from the analysis of the Kepler light curve. Results. We obtain T-eff, log g, v sin i, and the absolute masses and radii of the components, together with their flux ratio and separation. Whereas the secondary star rotates synchronously with the orbital motion, the primary star rotates subsynchronously by a factor of 0.75. The newly determined mass ratio of 0.0911 is higher than previously thought and means a detached configuration is required to fit the light curve. Conclusions. With its low orbital period and very low mass ratio, the system shows characteristics of the R CMa-type stars but differs from this group by being detached. Its current state is assumed to be that of a detached post-Algol binary system with a pulsating primary component.
    Astronomy and Astrophysics 09/2013; 557:79-. DOI:10.1051/0004-6361/201321400 · 4.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Context: In the near future, new instruments such as ESPRESSO will arrive, allowing us to reach a precision in radial-velocity measurements on the order of 10 cm/s. At this level of precision, several noise sources that until now have been outweighed by photon noise will start to contribute significantly to the error budget. The telluric lines that are not neglected by the masks for the radial velocity computation, here called micro-telluric lines, are one such noise source. Aims: In this work we investigate the impact of micro-telluric lines in the radial velocities calculations. We also investigate how to correct the effect of these atmospheric lines on radial velocities. Methods: The work presented here follows two parallel lines. First, we calculated the impact of the micro-telluric lines by multiplying a synthetic solar-like stellar spectrum by synthetic atmospheric spectra and evaluated the effect created by the presence of the telluric lines. Then, we divided HARPS spectra by synthetic atmospheric spectra to correct for its presence on real data and calculated the radial velocity on the corrected spectra. When doing so, one considers two atmospheric models for the synthetic atmospheric spectra: the LBLRTM and TAPAS. Results: We find that the micro-telluric lines can induce an impact on the radial velocities calculation that can already be close to the current precision achieved with HARPS, and so its effect should not be neglected, especially for future instruments such as ESPRESSO. Moreover, we find that the micro-telluric lines' impact depends on factors, such as the radial velocity of the star, airmass, relative humidity, and the barycentric Earth radial velocity projected along the line of sight at the time of the observation.
    Astronomy and Astrophysics 07/2014; 568. DOI:10.1051/0004-6361/201423723 · 4.38 Impact Factor