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RAVE stars in K2 : I. Improving RAVE red giants spectroscopy using asteroseismology from K2 Campaign 1

Valentini, M; Chiappini, C.; Davies, G. R.; Elsworth, Y. P.; Mosser, B.; Lund, M. N.; Miglio, A.; Chaplin, W. J.; Rodrigues, T. S. and Boeche, C., et al. (2017) In Astronomy and Astrophysics 600.
Abstract

We present a set of 87 RAVE stars with detected solar like oscillations, observed during Campaign 1 of the K2 mission (RAVE K2-C1 sample). This data set provides a useful benchmark for testing the gravities provided in RAVE data release 4 (DR4), and is key for the calibration of the RAVE data release 5 (DR5). The RAVE survey collected medium-resolution spectra (R = 7500) centred in the Ca II triplet(8600 Å) wavelength interval, which although being very useful for determining radial velocity and metallicity, even at low S/N, is known be affected by a log (g)-Teff degeneracy. This degeneracy is the cause of the large spread in the RAVE DR4 gravities for giants. The understanding of the trends and offsets that affects RAVE... (More)

We present a set of 87 RAVE stars with detected solar like oscillations, observed during Campaign 1 of the K2 mission (RAVE K2-C1 sample). This data set provides a useful benchmark for testing the gravities provided in RAVE data release 4 (DR4), and is key for the calibration of the RAVE data release 5 (DR5). The RAVE survey collected medium-resolution spectra (R = 7500) centred in the Ca II triplet(8600 Å) wavelength interval, which although being very useful for determining radial velocity and metallicity, even at low S/N, is known be affected by a log (g)-Teff degeneracy. This degeneracy is the cause of the large spread in the RAVE DR4 gravities for giants. The understanding of the trends and offsets that affects RAVE atmospheric parameters, and in particular log (g), is a crucial step in obtaining not only improved abundance measurements, but also improved distances and ages. In the present work, we use two different pipelines, GAUFRE and Sp-Ace, to determine atmospheric parameters and abundances by fixing log (g) to the seismic one. Our strategy ensures highly consistent values among all stellar parameters, leading to more accurate chemical abundances. A comparison of the chemical abundances obtained here with and without the use of seismic log (g) information has shown that an underestimated (overestimated) gravity leads to an underestimated (overestimated) elemental abundance (e.g. [Mg/H] is underestimated by ∼0.25 dex when the gravity is underestimated by 0.5 dex). We then perform a comparison between the seismic gravities and the spectroscopic gravities presented in the RAVE DR4 catalogue, extracting a calibration for log (g) of RAVE giants in the colour interval 0.50 < (J-KS) < 0.85. Finally, we show a comparison of the distances, temperatures, extinctions (and ages) derived here for our RAVE K2-C1 sample with those derived in RAVE DR4 and DR5. DR5 performs better than DR4 thanks to the seismic calibration, although discrepancies can still be important for objects for which the difference between DR4/DR5 and seismic gravities differ by more than ∼0.5 dex. The method illustrated in this work will be used for analysing RAVE targets present in the other K2 campaigns, in the framework of Galactic Archaeology investigations.

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Stars: abundances, Stars: fundamental parameters, Stars: late-type, Stars: oscillations, Surveys, Techniques: spectroscopic
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Astronomy and Astrophysics
volume
600
publisher
EDP Sciences
external identifiers
  • scopus:85017026031
  • wos:000400754000078
ISSN
0004-6361
DOI
10.1051/0004-6361/201629701
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English
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yes
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aba56268-f810-4e42-8e2f-6dcd68ee7d9b
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2017-05-02 09:43:01
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2017-09-18 13:33:37
@article{aba56268-f810-4e42-8e2f-6dcd68ee7d9b,
  abstract     = {<p>We present a set of 87 RAVE stars with detected solar like oscillations, observed during Campaign 1 of the K2 mission (RAVE K2-C1 sample). This data set provides a useful benchmark for testing the gravities provided in RAVE data release 4 (DR4), and is key for the calibration of the RAVE data release 5 (DR5). The RAVE survey collected medium-resolution spectra (R = 7500) centred in the Ca II triplet(8600 Å) wavelength interval, which although being very useful for determining radial velocity and metallicity, even at low S/N, is known be affected by a log (g)-T<sub>eff</sub> degeneracy. This degeneracy is the cause of the large spread in the RAVE DR4 gravities for giants. The understanding of the trends and offsets that affects RAVE atmospheric parameters, and in particular log (g), is a crucial step in obtaining not only improved abundance measurements, but also improved distances and ages. In the present work, we use two different pipelines, GAUFRE and Sp-Ace, to determine atmospheric parameters and abundances by fixing log (g) to the seismic one. Our strategy ensures highly consistent values among all stellar parameters, leading to more accurate chemical abundances. A comparison of the chemical abundances obtained here with and without the use of seismic log (g) information has shown that an underestimated (overestimated) gravity leads to an underestimated (overestimated) elemental abundance (e.g. [Mg/H] is underestimated by ∼0.25 dex when the gravity is underestimated by 0.5 dex). We then perform a comparison between the seismic gravities and the spectroscopic gravities presented in the RAVE DR4 catalogue, extracting a calibration for log (g) of RAVE giants in the colour interval 0.50 &lt; (J-K<sub>S</sub>) &lt; 0.85. Finally, we show a comparison of the distances, temperatures, extinctions (and ages) derived here for our RAVE K2-C1 sample with those derived in RAVE DR4 and DR5. DR5 performs better than DR4 thanks to the seismic calibration, although discrepancies can still be important for objects for which the difference between DR4/DR5 and seismic gravities differ by more than ∼0.5 dex. The method illustrated in this work will be used for analysing RAVE targets present in the other K2 campaigns, in the framework of Galactic Archaeology investigations.</p>},
  articleno    = {A66},
  author       = {Valentini, M and Chiappini, C. and Davies, G. R. and Elsworth, Y. P. and Mosser, B. and Lund, M. N. and Miglio, A. and Chaplin, W. J. and Rodrigues, T. S. and Boeche, C. and Steinmetz, M and Matijevič, G. and Kordopatis, G. and Bland-Hawthorn, J. and Munari, U and Bienaymé, O. and Freeman, K.~C. and Gibson, B. K. and Gilmore, G. and Grebel, E. K. and Helmi, A and Kunder, A. and McMillan, P. and Navarro, J. E. J. Garcia and Parker, Q. A. and Reid, David W. and Seabroke, G. and Sharma, S. and Siviero, A and Watson, F. and Wyse, R F G and Zwitter, T. and Mott, A},
  issn         = {0004-6361},
  keyword      = {Stars: abundances,Stars: fundamental parameters,Stars: late-type,Stars: oscillations,Surveys,Techniques: spectroscopic},
  language     = {eng},
  month        = {04},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {RAVE stars in K2 : I. Improving RAVE red giants spectroscopy using asteroseismology from K2 Campaign 1},
  url          = {http://dx.doi.org/10.1051/0004-6361/201629701},
  volume       = {600},
  year         = {2017},
}