# 2015A&A...574A..90A

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 Query : 2015A&A...574A..90A

2015A&A...574A..90A - Astronomy and Astrophysics, volume 574A, 90-90 (2015/2-1)

The magnetic fields at the surface of active single G-K giants.

AURIERE M., KONSTANTINOVA-ANTOVA R., CHARBONNEL C., WADE G.A., TSVETKOVA S., PETIT P., DINTRANS B., DRAKE N.A., DECRESSIN T., LAGARDE N., DONATI J.-F., ROUDIER T., LIGNIERES F., SCHROEDER K.-P., LANDSTREET J.D., LEBRE A., WEISS W.W. and ZAHN J.-P.

Abstract (from CDS):

We investigate the magnetic field at the surface of 48 red giants selected as promising for detection of Stokes V Zeeman signatures in their spectral lines. In our sample, 24 stars are identified from the literature as presenting moderate to strong signs of magnetic activity. An additional 7 stars are identified as those in which thermohaline mixing appears not to have occured, which could be due to hosting a strong magnetic field. Finally, we observed 17 additional very bright stars which enable a sensitive search to be performed with the spectropolarimetric technique. We use the spectropolarimeters Narval and ESPaDOnS to detect circular polarization within the photospheric absorption lines of our targets. We treat the spectropolarimetric data using the least-squares deconvolution method to create high signal-to-noise ratio mean Stokes V profiles. We also measure the classical S-index activity indicator for the Ca ii H&K lines, and the stellar radial velocity. To infer the evolutionary status of our giants and to interpret our results, we use state-of-the-art stellar evolutionary models with predictions of convective turnover times. We unambiguously detect magnetic fields via Zeeman signatures in 29 of the 48 red giants in our sample. Zeeman signatures are found in all but one of the 24 red giants exhibiting signs of activity, as well as 6 out of 17 bright giant stars. However no detections were obtained in the 7 thermohaline deviant giants. The majority of the magnetically detected giants are either in the first dredge up phase or at the beginning of core He burning, i.e. phases when the convective turnover time is at a maximum: this corresponds to a magnetic strip'' for red giants in the Hertzsprung-Russell diagram. A close study of the 16 giants with known rotational periods shows that the measured magnetic field strength is tightly correlated with the rotational properties, namely to the rotational period and to the Rossby number Ro. Our results show that the magnetic fields of these giants are produced by a dynamo, possibly of α-ω origin since Ro is in general smaller than unity. Four stars for which the magnetic field is measured to be outstandingly strong with respect to that expected from the rotational period/magnetic field relation or their evolutionary status are interpreted as being probable descendants of magnetic Ap stars. In addition to the weak-field giant Pollux, 4 bright giants (Aldebaran, Alphard, Arcturus, η Psc) are detected with magnetic field strength at the sub-Gauss level. Besides Arcturus, these stars were not considered to be active giants before this study and are very similar in other respects to ordinary giants, with S-index indicating consistency with basal chromospheric flux.

Journal keyword(s): stars: magnetic field - stars: late-type - stars: evolution - stars: rotation

Full paper

 Number of rows : 53
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 * 14 Cet PM* 00 35 32.8334053776 -00 30 20.198722752   6.368 5.936     F5V 126 0
2 * bet Cet PM* 00 43 35.37090 -17 59 11.7827 3.90 3.02 2.01 1.29 0.78 G9.5IIICH-1 508 0
3 * eta Psc ** 01 31 29.0102587 +15 20 44.968540 5.320 4.600 3.620 2.90 2.40 G7IIIa 240 0
4 V* OP And RS* 01 36 27.2005869192 +48 43 22.000439676   7.47 6.22     K1III: 97 0
5 * ups Per PM* 01 37 59.5569926 +48 37 41.569533 6.29 4.85 3.57 2.61 1.96 K3-IIICN0.5 225 0
6 HD 11812 * 01 56 49.7630628000 +38 01 21.696664764   9.57 9.13     F5.5IV-V(n) 24 0
7 * alf Ari PM* 02 07 10.40570 +23 27 44.7032 4.29 3.17 2.01 1.15 0.54 K2-IIIbCa-1 615 1
8 HD 22468 RS* 03 36 47.2911034958 +00 35 15.938962144 7.09 6.79 5.90 5.4   K2:Vnk 1146 0
9 HD 232862 ** 03 57 19.967736 +50 51 18.56412   10.47 9.58 9.36   K2V 27 0
10 V* EK Eri BY* 04 20 38.6418121776 -06 14 45.577773096   7.036 6.154     K0III 114 0
11 * tet01 Tau SB* 04 28 34.4960341 +15 57 43.849432 5.510 4.780 3.840 5.48   G9IIIFe-0.5 479 0
12 * eps Tau ** 04 28 37.0002551195 +19 10 49.563140930 5.42 4.54 3.53     G9.5IIICN0.5 567 1
13 Cl Melotte 25 OpC 04 29 47 +16 56.9           ~ 2843 0
14 * alf Tau LP? 04 35 55.23907 +16 30 33.4885 4.32 2.40 0.86 -0.37 -1.31 K5+III 1213 1
15 V* V1192 Ori RS* 05 00 08.2195942104 +03 17 12.024920724   8.75 7.503   6.223 K1/2III 82 0
16 * eps Lep PM* 05 05 27.6653698 -22 22 15.723893 6.41 4.64 3.18 2.08 1.27 K4III 150 0
17 HD 33798 ** 05 15 15.45749 +47 10 14.6314       7.55   G5III 75 0
18 * nu.03 CMa * 06 37 53.4213820872 -18 14 14.930466036 6.61 5.60 4.43 3.56 2.97 K1-III 83 0
19 HD 50885 * 07 01 21.4189944984 +70 48 29.863508724 8.550 7.030 5.690     K4III 22 0
20 * bet Gem PM* 07 45 18.94987 +28 01 34.3160 3.00 2.14 1.14 0.39 -0.11 K0IIIb 1075 1
21 * 19 Pup ** 08 11 16.3058502 -12 55 37.195175 6.44 5.68 4.72 3.99 3.51 G8.5IIIb 80 0
22 V* FI Cnc Ro* 08 32 17.3407945320 +29 19 09.519146040   8.32 7.35     G5 37 1
23 * zet Hya PM* 08 55 23.6261352 +05 56 44.035380 4.92 4.10 3.10 2.39 1.90 G8.5III 233 0
24 * alf Hya * 09 27 35.24270 -08 39 30.9583 5.14 3.42 1.97 0.93 0.16 K3IIIa 419 0
25 * d UMa RS* 09 34 28.8594727848 +69 49 49.226541888 5.67 5.34 4.57 3.91 3.50 G5III-IV 285 0
26 * ups01 Hya * 09 51 28.6938376 -14 50 47.771030 5.68 5.03 4.11 3.42 2.95 G7III 153 0
27 * gam Leo ** 10 19 58.35056 +19 50 29.3468   3.79 2.37     K1-III+G7IIIb 75 0
28 * gam01 Leo PM* 10 19 58.354462 +19 50 29.35920 4.13 3.13 1.98 1.13 0.51 K1-IIIFe-1 278 1
29 * nu. Hya PM* 10 49 37.4887449 -16 11 37.135989 5.62 4.35 3.11 2.17 1.53 K1.5IIIHdel-0.5 166 0
30 * alf UMa SB* 11 03 43.67152 +61 45 03.7249 3.78 2.86 1.79 0.98 0.40 G9III+A7.5 431 0
31 * eps Crv PM* 12 10 07.4805825 -22 37 11.161983 5.79 4.32 2.98 2.05 1.41 K2+IIIa 142 0
32 * 31 Com Ro* 12 51 41.9201696640 +27 32 26.565016812 5.81 5.61 4.94 4.39 4.04 G0IIIp 417 1
33 * 37 Com RS* 13 00 16.4694383232 +30 47 06.079456932   6.02 4.88     G9IIICH-2CN-1 153 0
34 * 7 Boo * 13 53 12.9300854664 +17 55 58.327270932   6.551 5.709     G5III 65 0
35 * alf Boo RG* 14 15 39.67207 +19 10 56.6730 2.46 1.18 -0.05 -1.03 -1.68 K1.5IIIFe-0.5 2223 0
36 * eps Boo A * 14 44 59.223146 +27 04 27.14599   3.61 2.45     K0-II-III 116 0
37 * bet UMi V* 14 50 42.32580 +74 09 19.8142 5.32 3.55 2.08 0.97 0.21 K4-III 316 0
38 * bet Boo Er* 15 01 56.7623786 +40 23 26.040607 5.21 4.47 3.52 2.85 2.37 G8IIIaFe-0.5 246 0
39 * del CrB RS* 15 49 35.6469970632 +26 04 06.214310112 5.80 5.43 4.63 4.00 3.58 G5III-IVFe-1 198 0
40 * kap Her A * 16 08 04.5256427568 +17 02 49.119104724   5.927 4.994     G7III 136 0
41 HD 150580 * 16 41 00.5816003808 +24 51 31.332323376   7.407 6.070     K2 25 0
42 * eta Her PM* 16 42 53.7650947 +38 55 20.112868 5.03 4.42 3.50 2.83 2.35 G7IIIFe-1 277 0
43 * ksi Her LP* 17 57 45.8857114 +29 14 52.367509 5.34 4.64 3.70 3.01 2.55 G8.5III 231 0
44 * nu. Oph PM* 17 59 01.5919129 -09 46 25.079852 5.20 4.33 3.34 2.64 2.16 G9IIIa 199 1
45 HD 178208 SB* 19 05 09.8405992032 +49 55 23.390884416 9.400 7.800 6.430     K3III 46 0
46 HD 186619 V* 19 43 45.0965622360 +41 46 23.199657276 9.40 7.41 5.84     M0III 43 0
47 HD 199101 * 20 53 53.8916816088 +33 26 16.413219312 8.86 6.99 5.47     K5III 49 0
48 * iot Cap BY* 21 22 14.7956478 -16 50 04.359799 5.74 5.18 4.27 3.65 3.17 G7IIIFe-1.5 186 0
49 * rho Cyg PM* 21 33 58.8530450102 +45 35 30.620055459 5.47 4.91 4.02 3.31 2.81 G8IIIFe-0.5 188 0
50 * mu. Peg PM* 22 50 00.1931506 +24 36 05.698380 5.10 4.42 3.48 2.80 2.33 G8+III 284 0
51 V* KU Peg RS* 23 05 29.2735048704 +26 00 33.459393312   8.79 7.66     G9IV(e) 61 0
52 * 4 And * 23 07 39.2672021448 +46 23 14.030186820   6.702 5.294     K5III 64 0
53 V* OU And Ro* 23 49 40.9595121216 +36 25 31.013370732   6.69 5.90     G1IIICaIIem 134 0

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2022.05.25-09:18:56