2012A&A...546A.117G

Query : 2012A&A...546A.117G

2012A&A...546A.117G - Astronomy and Astrophysics, volume 546A117-117 (2012/10-1)

Dynamo regime transition among sun-like stars in M 34. A time evolution model of X-ray activity on the main sequence.

GONDOIN P.

Abstract (from CDS):

The X-ray emission from late-type stars in open clusters exhibits two kinds of dependences on stellar rotation. While fast rotators have a relatively constant X-ray emission level, slower rotators show a decline of their X-ray emission with decreasing rotation rate. The physical significance of the transition between these two X-ray emission regimes is a matter of debate. During the ∼500Myr period of stellar evolution that separates the Pleiades from the Hyades, late-type stars such as those present in the M34 open cluster undergo significant changes in their rotation rates. These could affect the dynamo processes in their interiors, possibly altering their surface magnetic fluxes. The purpose of the present study is to look for the X-ray signatures of such possible modifications, to search for correlations with rotation and stellar parameters, and to propose a parameterization of the X-ray activity evolution on the main sequence. The aim is to provide observational constraints on the time evolution of dynamo processes in the interiors of late-type stars. The distributions of stellar X-ray luminosities vs. rotation periods and Rossby numbers of a sample of M34 late-type stars are compared with rotation-activity relationships established in a large sample of cluster members and field stars. A model of X-ray activity evolution is developed by combining an X-ray activity-rotation relationship with a recent model of stellar rotation evolution on the main sequence. The distribution of stellar X-ray luminosities in M34 is compared with this model. A correlation is observed between the saturated and non-saturated regime of X-ray emission and the C- and I-rotational sequences that have been observed in M34 from extensive rotational periods surveys. M34 sample stars show a steep transition in X-ray to bolometric luminosity ratio between the C-sequence and gap stars that emit close to the 10–3 saturation level, and the I-sequence stars, whose LX/Lbol ratio is significantly lower for similar values of the Rossby number. A comparison between X-ray emission vs. mass distribution in M34 and the X-ray luminosity evolution model suggests that the transition between the saturated and non-saturated regime of X-ray emission occurs in M34 cluster members depending on their convective turnover time and period of rotation. I argue that the drop of (LX/Lbol) by one order of magnitude observed in M34 around a Rossby number of 0.3 is indicative of a change in dynamo efficiency. I conclude that the transition from the saturated to the non-saturated regime of X-ray emission among main-sequence stars is the result of a dynamo regime transition, possibly between a turbulent dynamo and an interface-type dynamo.

Abstract Copyright: ∼

Journal keyword(s): open clusters and associations: individual: M 34 - stars: activity - stars: atmospheres - stars: late-type - stars: magnetic field - stars: rotation

Simbad objects: 53

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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 - 2026 		#notes
1 NGC 752 OpC 01 56 53.7 +37 45 06           ~ 712 0
2 Cl* NGC 1039 JP 1 * 02 40 35.89 +42 42 30.9     14.38     ~ 2 0
3 LB 3568 blu 02 40 40.0499030280 +42 46 32.339200620   18.5       ~ 3 0
4 NGC 1039 147 * 02 40 54.4487133696 +42 57 57.009238596   12.9 12.68     F2 6 0
5 [MMS2011] 8 Ro* 02 40 57.994 +42 49 44.61   17.993 17.136   16.075 ~ 3 0
6 Cl* NGC 1039 IAH 1-2573 * 02 41 04.2492118513 +42 35 11.934638085           ~ 5 0
7 2MASS J02413016+4227555 * 02 41 30.1669214472 +42 27 55.359553428           ~ 9 0
8 [MMS2011] 5 * 02 41 31.45 +42 59 05.8           ~ 2 0
9 NGC 1039 204 * 02 41 33.5880027312 +42 32 22.393865868   12.96 12.33     G0? 18 0
10 V* V797 Per BY* 02 41 35.2538631341 +42 41 02.494183444   15.406 14.546   13.552 ~ 15 0
11 V* V802 Per BY* 02 41 43.8644364744 +42 45 08.140027500   18.415 17.009   15.260 ~ 12 0
12 Cl* NGC 1039 IS 136 Ro* 02 41 47.3933506656 +42 43 38.754393924   13.765 13.151   12.433 ~ 17 0
13 V* V807 Per BY* 02 41 48.4792871832 +42 49 33.623050224   17.385 16.242   14.830 ~ 6 0
14 Cl* NGC 1039 IAH 1-2953 EB* 02 41 50.4889532917 +43 01 26.966054045           ~ 5 0
15 V* V813 Per BY* 02 41 53.2458485280 +42 35 26.296274364   17.519 16.294 15.59 14.660 ~ 8 0
16 V* V817 Per BY* 02 41 55.2544600944 +42 50 31.764286788           ~ 9 0
17 Cl* NGC 1039 JP 265 Ro* 02 41 57.4732127038 +43 00 26.509711996   16.564 15.503   14.241 ~ 9 0
18 V* V821 Per BY* 02 42 01.8112260336 +42 41 58.981967592           ~ 9 0
19 [MMS2011] 21 * 02 42 05.12 +42 25 26.5           ~ 2 0
20 Cl* NGC 1039 IAH 1-1178 * 02 42 06.4950070104 +42 39 37.270747584           ~ 9 0
21 NGC 1039 OpC 02 42 09.1 +42 44 02           ~ 467 0
22 2XMM J024136.6+425020 EB* 02 42 10.4188587663 +42 46 33.371540637           ~ 5 0
23 V* V837 Per BY* 02 42 17.2368045024 +42 48 18.652306824   17.02 15.86     ~ 15 0
24 Cl* NGC 1039 JP 358 * 02 42 17.4198404112 +42 35 04.042767264   16.16 15.84     ~ 3 0
25 [MMS2011] 24 * 02 42 26.03 +42 48 53.9           ~ 2 0
26 V* V846 Per BY* 02 42 31.5394551744 +42 37 10.527987612   17.01 15.93     ~ 14 0
27 V* V847 Per BY* 02 42 32.2848031100 +42 49 05.945042396   16.1 15.02     ~ 20 0
28 NGC 1039 352 * 02 42 34.3231339344 +42 36 22.247813556   13.05 12.40 12.27   ~ 18 0
29 V* V852 Per BY* 02 42 35.0221423680 +42 39 28.967335596           ~ 5 0
30 V* V857 Per BY* 02 42 41.8213264200 +42 46 01.798604616           ~ 5 0
31 NGC 1039 367 * 02 42 42.4480159944 +42 40 31.438108992   13.17 12.82     ~ 12 0
32 V* V861 Per BY* 02 42 47.5496696304 +42 45 46.817005248   17.81 16.68     ~ 14 0
33 [MMS2011] 28 * 02 42 47.89 +43 00 47.2           ~ 2 0
34 UCAC4 664-012210 ** 02 42 49.202688 +42 40 15.38724   15.85 14.98 14.87   ~ 2 0
35 V* V864 Per BY* 02 42 50.7705996312 +42 58 07.851505080     14.88     ~ 12 0
36 V* V868 Per BY* 02 42 57.8371844703 +42 58 03.854880882   15.79 14.85     ~ 14 0
37 V* V869 Per BY* 02 42 57.8756975232 +42 41 46.559011992     16.53     ~ 4 0
38 V* V870 Per BY* 02 42 59.9525908032 +42 58 01.516181844   16.67 15.67     ~ 10 0
39 Cl* NGC 1039 IAH 4-2533 * 02 43 01.9938104592 +42 46 54.212404944           ~ 11 0
40 Cl* NGC 1039 JP 582 EB* 02 43 13.1016949080 +42 50 25.453610448     16.15     ~ 7 0
41 2MASS J02432379+4230590 * 02 43 23.7984595997 +42 30 59.007624668           ~ 11 0
42 Cl* NGC 1039 JP 612 * 02 43 30.2815113120 +42 53 02.624697312   15.81 14.88     ~ 10 0
43 Cl* NGC 1039 IS 298 * 02 43 31.9613261400 +42 38 31.562060208   14.25 13.52     ~ 13 0
44 Cl Melotte 20 MGr 03 26 50.6 +48 51 48           ~ 928 0
45 Cl Melotte 22 OpC 03 46 38.0 +24 10 41           ~ 3679 0
46 Cl Melotte 25 OpC 04 30 27.4 +16 46 43           ~ 3309 0
47 NGC 2516 OpC 07 58 00.5 -60 46 36           ~ 793 0
48 NGC 2547 OpC 08 10 01.5 -49 12 08           ~ 445 0
49 NGC 2632 OpC 08 39 58.4 +19 36 33           ~ 1733 0
50 IC 2391 OpC 08 41 17.5 -53 03 00           ~ 871 0
51 IC 2602 OpC 10 42 55.9 -64 25 22           ~ 735 0
52 NGC 3532 OpC 11 05 33.9 -58 42 13           ~ 414 0
53 NGC 6475 OpC 17 53 44.1 -34 49 36           ~ 413 0

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