Spectroscopic and astrometric radial velocities: Hyades as a benchmark

Leão, I. C.; Pasquini, L.; Ludwig, H.‐G.; Medeiros, J. R. De

doi:10.1093/mnras/sty3215

Cited by 21 publications

(19 citation statements)

References 44 publications

(64 reference statements)

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“…the fine strucure constant, α, Dzuba et al 1999;Webb et al 1999Webb et al , 2011King et al 2012, and others). It is also the method proposed to measure the expansion of the Universe in "real time" and in a model-independent way (also known as the Sandage test or the "redshift drift" measurement, Sandage (1962); Loeb (1998); Liske et al (2008)) and to map the gravitational potential of the Galaxy (Ravi et al 2019;Leão et al 2019). These science goals are important drivers for all 30-meter class telescopes planned for the 2020s, i.e.…”

Section: Introductionmentioning

confidence: 99%

Precision and consistency of astrocombs

Milaković

Pasquini

Webb

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Astrocombs are ideal spectrograph calibrators whose limiting precision can be derived using a second, independent, astrocomb system. We therefore analyse data from two astrocombs (one 18 GHz and one 25 GHz) used simultaneously on the HARPS spectrograph at the European Southern Observatory. The first aim of this paper is to quantify the wavelength repeatability achieved by a particular astrocomb. The second aim is to measure wavelength calibration consistency between independent astrocombs, that is to place limits or measure any possible zero-point offsets. We present three main findings, each with important implications for exoplanet detection, varying fundamental constant and redshift drift measurements. Firstly, wavelength calibration procedures are important: using multiple segmented polynomials within one echelle order results in significantly better wavelength calibration compared to using a single higher-order polynomial. Segmented polynomials should be used in all applications aimed at precise spectral line position measurements. Secondly, we found that changing astrocombs causes significant zero-point offsets (≈ 60 cm s −1 in our raw data) which were removed. Thirdly, astrocombs achieve a precision of 4 cm s −1 in a single exposure (≈ 10% above the measured photon-limited precision) and 1 cm s −1 when time-averaged over a few hours, confirming previous results. Astrocombs therefore provide the technological requirements necessary for detecting Earth-Sun analogues, measuring variations of fundamental constants and the redshift drift.

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Section: Introductionmentioning

confidence: 99%

Precision and consistency of astrocombs

Milaković

Pasquini

Webb

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…In most stars the GR is of a few hundred metres per second, comparable to the convective blueshifts in stellar atmospheres (see e.g. Allende Prieto et al 2002;Leão et al 2019), but in WDs the GR signal is very pronounced (tens of km s −1 ), and, if hotter than ∼14 000 K, no other mechanism capable of shifting the lines of these stars is expected to be present (Allende Prieto et al 2002;Tremblay et al 2013). This implies that the difference between A&A 627, L8 (2019) the spectroscopic Doppler shifts and the astrometric radial velocity can be attributed entirely to GR, making the measurement potentially very accurate.…”

Section: Introductionmentioning

confidence: 93%

“…The Doppler shifts were subsequently corrected for the astrometric radial velocity of each star and for the cluster rotation, though the latter is less than 300 ms −1 for the sample stars (Leão et al 2019), providing the GR for each star. All the values obtained are given in Table 1.…”

Section: Doppler Shift and Gr Measurementsmentioning

confidence: 99%

“…We think that it is now possible to observationally determine Based on UVES data from the ESO VLT archive. the masses of the Hyades WDs with good accuracy because (i) Gaia provides very accurate distances (to better than 0.5%) for these stars, and (ii) the Hyades cluster radial velocity is known with an uncertainty of about 100 ms −1 (Leão et al 2019). These latter authors have also shown that spectroscopic and astrometric radial velocities agree to better than ∼30 ms −1 once the additional causes of line shifts are properly taken into account: gravitational redshift, atmospheric convective motions, and cluster rotation.…”

Section: Introductionmentioning

confidence: 99%

“…These latter authors have also shown that spectroscopic and astrometric radial velocities agree to better than ∼30 ms −1 once the additional causes of line shifts are properly taken into account: gravitational redshift, atmospheric convective motions, and cluster rotation. After applying these corrections, the cluster velocity dispersion is small: less than 340 ms −1 (Leão et al 2019). Therefore, in principle, by measuring the spectral Doppler shift of the WDs in the Hyades, their gravitational redshift (GR) can be derived with an error of ∼300 ms −1 .…”

Section: Introductionmentioning

confidence: 99%

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Masses of the Hyades white dwarfs

Pasquini¹,

Pala²,

Ludwig

et al. 2019

A&A

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Context. It is possible to accurately measure the masses of the white dwarfs (WDs) in the Hyades cluster using gravitational redshift, because the radial velocity of the stars can be obtained independently of spectroscopy from astrometry and the cluster has a low velocity dispersion. Aims. We aim to obtain an accurate measurement of the Hyades WD masses by determining the mass-to-radius ratio (M/R) from the observed gravitational redshift, and to compare them with masses derived from other methods. Methods. We analyse archive high-resolution UVES-VLT spectra of six WDs belonging to the Hyades to measure their Doppler shift, from which M/R is determined after subtracting the astrometric radial velocity. We estimate the radii using Gaia photometry as well as literature data. Results. The M/R error associated to the gravitational redshift measurement is about 5%. The radii estimates, evaluated with different methods, are in very good agreement, though they can differ by up to 4% depending on the quality of the data. The masses based on gravitational redshift are systematically smaller than those derived from other methods, by a minimum of ∼0.02 up to 0.05 solar masses. While this difference is within our measurement uncertainty, the fact that it is systematic indicates a likely real discrepancy between the different methods. Conclusions. We show that the M/R derived from gravitational redshift measurements is a powerful tool to determine the masses of the Hyades WDs and could reveal interesting properties of their atmospheres. The technique can be improved by using dedicated spectrographs, and can be extended to other clusters, making it unique in its ability to accurately and empirically determine the masses of WDs in open clusters. At the same time we prove that gravitational redshift in WDs agrees with the predictions of stellar evolution models to within a few percent.

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The Gaia-ESO survey: the non-universality of the age–chemical-clocks–metallicity relations in the Galactic disc

Casali

Spina

Magrini

et al. 2020

A&A

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Context. In the era of large spectroscopic surveys, massive databases of high-quality spectra coupled with the products of the Gaia satellite provide tools to outline a new picture of our Galaxy. In this framework, an important piece of information is provided by our ability to infer stellar ages, and consequently to sketch a Galactic timeline. Aims. We aim to provide empirical relations between stellar ages and abundance ratios for a sample of stars with very similar stellar parameters to those of the Sun, namely the so-called solar-like stars. We investigate the dependence on metallicity, and we apply our relations to independent samples, that is, the Gaia-ESO samples of open clusters and of field stars. Methods. We analyse high-resolution and high-signal-to-noise-ratio HARPS spectra of a sample of solar-like stars to obtain precise determinations of their atmospheric parameters and abundances for 25 elements and/or ions belonging to the main nucleosynthesis channels through differential spectral analysis, and of their ages through isochrone fitting. Results. We investigate the relations between stellar ages and several abundance ratios. For the abundance ratios with a steeper dependence on age, we perform multivariate linear regressions, in which we include the dependence on metallicity, [Fe/H]. We apply our best relations to a sample of open clusters located from the inner to the outer regions of the Galactic disc. Using our relations, we are able to recover the literature ages only for clusters located at RGC > 7 kpc. The values that we obtain for the ages of the inner-disc clusters are much greater than the literature ones. In these clusters, the content of neutron capture elements, such as Y and Zr, is indeed lower than expected from chemical evolution models, and consequently their [Y/Mg] and [Y/Al] are lower than in clusters of the same age located in the solar neighbourhood. With our chemical evolution model and a set of empirical yields, we suggest that a strong dependence on the star formation history and metallicity-dependent stellar yields of s-process elements can substantially modify the slope of the [s/α]–[Fe/H]–age relation in different regions of the Galaxy. Conclusions. Our results point towards a non-universal relation [s/α]–[Fe/H]–age, indicating the existence of relations with different slopes and intercepts at different Galactocentric distances or for different star formation histories. Therefore, relations between ages and abundance ratios obtained from samples of stars located in a limited region of the Galaxy cannot be translated into general relations valid for the whole disc. A better understanding of the s-process at high metallicity is necessary to fully understand the origin of these variations.

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Spectroscopic and astrometric radial velocities: Hyades as a benchmark

Cited by 21 publications

References 44 publications

Precision and consistency of astrocombs

Precision and consistency of astrocombs

Masses of the Hyades white dwarfs

The Gaia-ESO survey: the non-universality of the age–chemical-clocks–metallicity relations in the Galactic disc

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