2017ApJ...840...67L


C.D.S. - SIMBAD4 rel 1.7 - 2019.12.12CET06:41:15

2017ApJ...840...67L - Astrophys. J., 840, 67-67 (2017/May-2)

On the origin of sub-subgiant stars. II. Binary mass transfer, envelope stripping, and magnetic activity.

LEINER E., MATHIEU R.D. and GELLER A.M.

Abstract (from CDS):

Sub-subgiant stars (SSGs) lie to the red of the main sequence and fainter than the red giant branch in cluster color-magnitude diagrams (CMDs), a region not easily populated by standard stellar evolution pathways. While there has been speculation on what mechanisms may create these unusual stars, no well-developed theory exists to explain their origins. Here we discuss three hypotheses of SSG formation: (1) mass transfer in a binary system, (2) stripping of a subgiant's envelope, perhaps during a dynamical encounter, and (3) reduced luminosity due to magnetic fields that lower convective efficiency and produce large starspots. Using the stellar evolution code MESA, we develop evolutionary tracks for each of these hypotheses, and compare the expected stellar and orbital properties of these models with six known SSGs in the two open clusters M67 and NGC 6791. All three of these mechanisms can create stars or binary systems in the SSG CMD domain. We also calculate the frequency with which each of these mechanisms may create SSG systems, and find that the magnetic field hypothesis is expected to create SSGs with the highest frequency in open clusters. Mass transfer and envelope stripping have lower expected formation frequencies, but may nevertheless create occasional SSGs in open clusters. They may also be important mechanisms to create SSGs in higher mass globular clusters.

Abstract Copyright: © 2017. The American Astronomical Society. All rights reserved.

Journal keyword(s): binaries: spectroscopic - galaxies: clusters: individual: (M67, NGC 6791) - stars: magnetic field - stars: mass-loss - starspots - starspots

CDS comments: Table 3: WOCS 12270 is not in SIMBAD.

Simbad objects: 14

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Number of rows : 14

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 188 OpC 00 48 26 +85 15.3           ~ 796 0
2 NGC 2168 OpC 06 08 54 +24 20.0           ~ 449 0
3 NGC 2682 OpC 08 51 18 +11 48.0           ~ 1991 0
4 NGC 6397 GlC 17 40 42.09 -53 40 27.6   7.39 5.17     ~ 1761 1
5 V* Z Her RS* 17 58 06.9787072966 +15 08 21.909354791   7.86 7.30     F8V 268 0
6 Cl* NGC 6791 SBG 83 * 19 20 10.62 +37 51 11.6     18.30   16.80 ~ 3 0
7 [HGM2009b] WOCS 147014 V* 19 20 21.4859368993 +37 48 21.600889408     17.781 17.221   ~ 6 0
8 V* V598 Lyr BY* 19 20 38.8884148067 +37 49 04.309333129   19.172 17.949 17.279 16.64 ~ 13 0
9 NGC 6791 OpC 19 20 53 +37 46.3   10.52 9.5     ~ 847 0
10 [DPM2007] 01431-10 V* 19 21 25.203 +37 45 49.72   19.004 17.669   16.217 ~ 3 0
11 2MASS J19411327+4007559 * 19 41 13.2705108380 +40 07 55.924012717     15.07   14.24 ~ 2 0
12 NGC 6819 OpC 19 41 18 +40 11.2   8.21 7.3     ~ 447 0
13 [GXC2015] 295.33837+40.15633 * 19 41 21.2113778518 +40 09 22.746657505     14.37   13.93 ~ 4 0
14 2MASS J19420737+4001403 * 19 42 07.3838753484 +40 01 40.266897258     13.82   12.40 ~ 2 0

    Equat.    Gal    SGal    Ecl

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2019.12.12-06:41:15

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