J/AJ/169/145 Resolved binary stars in Pleiades (Chulkov+, 2025) ================================================================================ Resolving Pleiades binary stars with Gaia and speckle interferometric observations. Chulkov D., Strakhov I., Safonov B. =2025AJ....169..145C (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Interferometry; Stars, double and multiple; Clusters, open Keywords: Open star clusters - Speckle interferometry - Visual binary stars Abstract: The Pleiades is the most prominent open star cluster visible from Earth and an important benchmark for simple stellar populations unified by common origin, age, and distance. Binary stars are its essential ingredient, yet their contribution remains uncertain due to heavy observational biases. A resolved multiplicity survey was conducted for a magnitude-limited G<15mag sample of 423 potential cluster members, including sources with poorly fitted astrometric solutions in Gaia DR3. Speckle interferometric observations at the 2.5 meter telescope of the Sternberg Astronomical Institute, Moscow State University observatory were combined with Gaia data, enabling the identification of 61 resolved binary or multiple systems within the 0.04-10arcsec (5-1350au) separation range. With speckle observations, we discovered 21 components in 20 systems. The existence of a Merope (23 Tau) companion is confirmed after several previous unsuccessful attempts. We show that the Gaia multipeak fraction is a strong predictor of subarcsecond multiplicity, as all sources with ipd_frac_multi_peak > 4% are successfully resolved. We found that 10% of Pleiades stars have a companion with a mass ratio q>0.5 within the projected separation of 27300au. An observed dearth of wide pairs with a large mass ratio (q>0.55) may imprint the transition from hard to soft binaries regime at the early stages of cluster evolution. The total binary fraction for q>0.5 systems is extrapolated to be around 25%. Description: The results of a resolved multiplicity survey in Pleiades. Systems with at least one component having an apparent magnitude G<15 mag are considered. The list of cluster members from Chulkov (2024AJ....168..156C, Cat. J/AJ/168/156) serves as the input sample. Speckle observations were conducted with the 2.5-meter telescope of the Sternberg Astronomical Institute, Moscow State University observatory. Table 2 contains Gaia-resolved pairs with angular separation within 10 arcsec. Table 3 includes systems resolved with speckle interferometric observations, with angular separation within 1.05 arcsec. Table 5 includes a list of individual observations for speckle-resolved binaries. The detection limits for all entries are provided in Table 6. Contrast curve and autocorrelation function plots for all observations are stored at https://doi.org/10.5281/zenodo.14252721 . Objects: ----------------------------------------------------- RA (2000) DE Designation(s) ----------------------------------------------------- 03 46 24.24 +24 06 50.4 Pleiades = Cl Melotte 22 ----------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 116 38 List of resolved Gaia DR3 systems in Pleiades table3.dat 96 54 List of speckle-resolved systems in Pleiades table5.dat 95 166 Observations of speckle-resolved Pleiades Stars table6.dat 69 667 Detection limits for Pleiades sample stars -------------------------------------------------------------------------------- See also: I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022) J/AJ/168/156 : Observational sample of Pleaides stars (Chulkov, 2024) Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 10 A10 --- WDS WDS Identification (J2000) 12- 28 I17 --- Gaia1 Gaia DR3 designation of primary source 30- 35 F6.3 mag Gmag1 Gaia DR3 G magnitude of primary source 37- 40 F4.2 Msun m1 Isochrone-estimated mass of primary star 42- 45 F4.2 Msun e_m1 Primary mass uncertainty 47- 63 I17 --- Gaia2 Gaia DR3 designation of secondary source 65- 70 F6.3 mag Gmag2 Gaia DR3 G magnitude of secondary source 72- 75 F4.2 Msun m2 Isochrone-estimated mass of secondary star 77- 80 F4.2 Msun e_m2 Secondary mass uncertainty 82- 85 F4.2 arcsec Sep Angular separation 87- 90 F4.2 mas/yr rel-PM ? Relative proper motion of components 92- 95 F4.2 --- Plxdev ? Parallax deviation (see Equation 2) 97-100 F4.2 --- Prob Chance alignment probability 102-106 F5.3 --- q Estimated mass ratio 108-112 F5.3 --- e_q Mass ratio uncertainty 114-116 A3 --- Notes [CFPRSW,] Notes (1) -------------------------------------------------------------------------------- Note (1): Notes as follows: C = multiplicity is suspected from color-magnitude diagram analysis F = possible cluster nonmember P = secondary magnitude is derived from isochrone R = the system has speckle-resolved companion within 1 arcsec (Table 3) S = spectroscopic binarity related to unresolved companion W = WDS identifier is newly introduced -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 10 A10 --- WDS WDS Identification (J2000) 12- 28 I17 --- Gaia Gaia DR3 designation of primary source 30- 35 F6.3 mag Gmag Gaia DR3 G magnitude of primary source 37- 44 F8.3 yr Date Observation date 46- 49 F4.2 arcsec Sep Angular separation 51 A1 --- Band [Iyz] Passband of the filter (1) 53- 55 F3.1 mag Delm Magnitude contrast 57- 60 F4.2 Msun m1 Isochrone-estimated mass of primary star 62- 65 F4.2 Msun e_m1 Primary mass uncertainty 67- 70 F4.2 Msun m2 Isochrone-estimated mass of primary star 72- 75 F4.2 Msun e_m2 Secondary mass uncertainty 77- 80 F4.2 --- b_q Lower bound of mass ratio m1/m2 82- 85 F4.2 --- q Mass ratio m1/m2 87- 90 F4.2 --- B_q Upper bound of mass ratio m1/m2 92- 96 A5 --- Notes [BDFGNSTW,] Notes (2) -------------------------------------------------------------------------------- Note (1): Passband of the filter as follows: I = Ic Johnson-Cousins passband y = 550nm 50nm half-width passband z = 880nm 70nm half-width passband Note (2): Notes as follows B = source is blended; G-band magnitude represents the total flux D = a distant companion is present in Gaia (Table 2) F = possibly a cluster nonmember G = this pair is Gaia resolved (Table 2) N = the companion is previously unreported S = spectroscopic binarity related to unresolved companion T = three resolved components within 1 arcsec. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 17 I17 -- Gaia Gaia DR3 designation 19- 28 A10 -- WDS Washington Double Star Catalog designation 30- 35 F6.3 mag Gmag Gaia DR3 G magnitude 37- 44 F8.3 yr Date Observation date 46 A1 -- Band [IRyz] Passband of the filter (1) 48- 51 F4.2 arcsec Seeing Seeing during observations 53 I1 -- Pair Pair number within multiple system 55- 60 F6.4 arcsec Sep Angular separation 62- 67 F6.4 arcsec e_Sep Angular separation uncertainty 69- 74 F6.2 deg PA Position angle 76- 79 F4.2 deg e_PA Position angle uncertainty 81- 84 F4.2 mag Delm Magnitude contrast 86- 89 F4.2 mag e_Delm Magnitude contrast intrinsic uncertainty 91- 95 A5 -- Notes [PRUWq,] Notes (2) -------------------------------------------------------------------------------- Note (1): Passband of the filter as follows: I = Ic Johnson-Cousins passband R = Rc Johnson-Cousins passband y = 550nm 50nm half-width passband z = 880nm 70nm half-width passband Note (2): Notes as follows: P = 180 degree ambiguity in position angle R = no reference star used; contrast estimation less accurate U = unreliable contrast due to anisoplanatism W = WDS designation newly introduced q = observation used for q calculation -------------------------------------------------------------------------------- Byte-by-byte Description of file: table6.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 17 I17 -- Gaia Gaia DR3 designation 19- 24 F6.3 mag Gmag ? Gaia DR3 G magnitude 26- 33 F8.3 yr Date Observation date 35 A1 -- Band [IRyz] Passband of the filter (1) 37- 40 F4.2 arcsec Seeing Seeing during observations 42- 45 F4.2 mag Delm01 Detection limit at 0.1 arcsec 47- 50 F4.2 mag Delm02 Detection limit at 0.2 arcsec 52- 55 F4.2 mag Delm04 Detection limit at 0.4 arcsec 57- 60 F4.2 mag Delm06 Detection limit at 0.6 arcsec 62- 65 F4.2 mag Delm10 Detection limit at 1.0 arcsec 67- 69 A3 -- Notes [bd,] Notes (2) -------------------------------------------------------------------------------- Note (1): Passband of the filter as follows: I = Ic Johnson-Cousins passband R = Rc Johnson-Cousins passband y = 550nm 50nm half-width passband z = 880nm 70nm half-width passband Note (2): Notes as follows: b = system is successfully resolved, see binarity parameters in Table 5 d = detection limits are affected (degraded) by the resolved component -------------------------------------------------------------------------------- Acknowledgements: Dmitry Chulkov, chulkovd(at)gmail.com ================================================================================ (End) Patricia Vannier [CDS] 27-Feb-2025