### Working group results

Question 1: The Solar Twin Search So Far: Solar twins have been selected on the basis of specific observational parameters, and there are a large number of these to choose from.
[1A] How have the following parameters been employed in the solar analog hunt to date, and what has been the success or failure in identifying solar analogs in terms of those parameters?

Moderators evaluated their group's response and ranked the opinions on a scale of 5 (highly successful) to 1 (completely unsuccessful), or zero (not applicable). In addition, they noted the level agreement among the group by a sigma that ranged from zero (unanimous agreement) to three (significant disagreement). In the table below, we list the twenty parameters given to the groups for discussion. Each group evaluated four parameters, so that each parameter was evaluated independently, in the morning and afternoon, by two different groups of astronomers.

Table 1. Parameters that have been used to find solar analogs/twins
Parameter Group Ranking Remarks
Teff 1 3 ± 2 Useful if spectroscopically derived, usually in a differential context
6 4 ± 1 Concern over spread of Teff measures. Depends on model quality
log g 5 3 ± 2 Important, always available, but indirect
10 0 ± 0
Mbol 5 5 ± 1 Fundamental
10 5 ± 0
B-V 2 2 ± 1 Good for finding analogs; poor for finding twins
7 4 ± 0 High utility as a guide, exists for many stars
Johnson other than B-V 4 3 ± 0
9 3 ± 1 Relative ranking of homogeneous data OK.
V magnitude 4 0 ± 0 Not relevant
9 4 ± 1 MV very important; therefore mv is important.
[Fe/H] 3 4 ± 0
8 4 ± 0 Not a good parameter for first cut.
v sin i 5 2 ± 0 Allows you to differentiate the young stars. More needed!
10 0 ± 0
Inclination 4 0 ± 0
9 0 ± 0 Has been ignored to date; maybe interesting for future.
Microturbulence 3 1 ± 1
8 0 ± 0 Important, but subtle. Probably not important for solar twin search.
B field 5 1 ± 0 What many people are after, but not used to find solar analogs
10 0 ± 0
MK type 3 5 ± 0
8 5 ± 0 Good first cut for general search, but must recognize limitations
Cousins photometry 1 4 ± 1 V-I useful, but not as good as b-y for fainter stars
6 2 ± 1 Not used except as transformed to Johnson. Maybe better than B-V
Strömgren photometry 2 5 ± 0 Far superior to UBV; gives m1 and c1 indices
7 3 ± 2 b-y not much employed
Energy distribution 1 3 ± 2 Pretty useless: not enough + sys. errors. But, fundamental quantity
6 2 ± 0 Not enough stars for which this is available
Photometric var. 1 3 ± 2 Ancillary parameter
6 1 ± 0 Viewed as a proxy for "activity" or youth
Spectroscopic var. 2 1 ± 0 Not utilized efficiently yet
7 0 ± 0 Not for screening purposes, but useful as ancillary quantity
R'HK 2 4 ± 1 Useful if you closely examine the photospheric contribution
7 3 ± 2 Surrogate for age, but not very accurate. Starting point/screening
Location 4 2 ± 0 Space motions
9 1 ± 0 except as cluster membership determinant
Space velocity 3 2 ± 1
8 2 ± 0 Might indicate place of origin, but not good for first cut.

[1B] Are there any relevant parameters that have so far been ignored (both in the literature and in the list of 20 parameters supplied to the working groups) or inadequately considered, and what would be the specific insights gained from considering them? Determine up to two that are most important.

Working groups were asked to select one or two of the most important neglected parameters in the solar analog hunt so far, and to summarize the specific insights to be gained from using those parameters as selection criteria. The results are compiled in Table 2 below. Each parameter is lsited in a separate row, with the number of groups mentioning it and their remarks included in the second and third columns.

Table 2. Parameters that have been neglected in searching for solar twins.
Parameter # of times cited Insights to be gained from using this parameter
Companionship 6 In terms of stellar and/or planetary companions
LX 4 More broadly: parameters that measure activity in higher levels of the atmosphere, e.g., UV, Mg II h&k.
UV spectrophotometry 3
Radio luminosity 2 10 cm: variable, sensitive to spots
Geneva photometry 1 More precise measurements than Johnson & different from Strömgren.
Detailed abundances 1 i.e., CNO, He, not just [Fe/H]
Galactic orbit 1 Useful combination of location and velocity
Convection 1 The group feels this is an underappreciated parameter in evolution/interior models
Prot 1
Intellegent [sic] life 1

Question 2: The Solar Twin Search Following This Workshop: What is the optimum method for searching for solar twins?
[2A] Which, if any, parameters must be used in any search for solar twins (determine up to four)?

Groups listed up to four parameters they considered essential in future searches for solar analogs and twins. Again, a one-to-five scale was used to indicate the level of agreement (or lack thereof) among the group members.

Table 3. Parameters/techniques that must be considered in future solar twin searches
Parameter Rank (group #)
MV 5 (2), 5 (4), 5 (5), 5 (6), 5 (7), 5 (8), 5 (10)
Metallicity 5 (4), 3 (5), 5 (6), 5 (7), 5 (8), 5 (10)
Activity 4.5 (3), 5 (4), 3 (5), 5 (6), 5 (9), 5 (10)
Prot 5 (2), 5 (7), 5 (8)
Teff 4.5 (3), 5 (4), 5 (5), 5 (6), 5 (10)
Strömgren photometry 4 (2), 5 (8), 4 (9)
MK Type 4.5 (3), 4 (9)
Parallax (distance) 4.5 (3), 5 (9)
High-res spectroscopy 4 (2)
Mass 1 (7)
Age 1 (7)
Hour angle 1 (5)a
a Acknowledged by group during plenary session as a joke.''

[2B] Do the parameters employed depend on the research needs of the investigator, e.g., would an investigator working with UV data have fundamentally different search criteria than one working in the IR?

### YES!

[C] Can (or should) the essential parameters identified in [A] above be ranked in order of preference? That is, what is the optimum, properly ordered set of "filters" for identifying solar twins?

Table 4. Should the essential parameters be ranked in order of preference?
Group # Remark
2 No. It depends on the research needs of the investigator.
6 Only to the extent that they can be separated.
7 No. All are important at once.
10 No.

Table 5. If the parameters are ranked, in what order are they placed?}
Group \# 1st 2nd 3rd 4th
2 MV Strömgren Hi-res spectroscopy Prot
3 MK Type Teff, log g, metallicity parallax/Distance Activity
4 Color MV Metallicity Age
5 Teff MV Prot Composition
6 Teff MV Metallicity Activity
8 Colors MV Composition Rotation
9 MK Type Strömgren MV Activity

Question 3: Optimum Candidates Rank the following stars (listed by HD number) in order of preference as solar twins, to the extent that the working group considers feasible and/or useful. Each group may add up to 2 stars to the list. The stars are: 1835 (9 Cet), 11131, 20630 (kappa Cet), 28099 (VB 64), 44594, 76151, 86728, 89010, 114710 (beta Com), 144585, 146233 (18 Sco), 186408 (16 Cyg A), 186427 (16 Cyg B), 187923A, 217014 (51 Peg).

Table 6. Remarks about individual stars
1835 Good analog for young Sun; too late, too young
10307 Deserves study
11131 A little too hot; worth keeping; young; good analog, poor twin
20630 Too young; G5 V; poor analog
28099 Hyades member; analog, NOT twin; too young
44594 worth following up; young; HIPPARCOS parallax OK?; good analog
76151 Probably too young; too active; S too high; binary?
86728 Worth keeping in spite of MK type; too red; too problematic
89010 Too bright, too evolved; too bright
114710 Too young, too active, too hot; too active
144585 Too evolved; too luminous
alpha Cen A Twin of 186408; analog, not twin
146233 A keeper; best of the bunch
186408 Older than Sun; analog, not twin; good twin
186427 Older than Sun; analog, not twin; good twin
187923A Abundances too far off; spectral type off
217014 Good candidate!

Table 7. Optimum solar twin candidates
Rank 1st 2nd3rd4th5th6th7th8th9th
1 146233 146233 146233 146233 146233 146233 146233 146233 146233
2 217014 186408 186408 186408 217014 186408 186408 186408 186427
3 186408 186427 186427 217014 186427 186427 186427 186427 186408
4 186427 28099 217014 89010 44594 217014 217014 143761 217014
5 44594 1835 44594 28099
6 86728 11131 186408
7 76151 76151\alpha Cen A
8 alpha Cen A 186427 11131
9 144585 10307
10 20630 76151
11 28099 187923
12 89010
13 1835 1835
14 114710 20630
15 187923A 28099

[Contents]