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How Far Away One Can Penetrate with Gaia in Star Cluster Studies?

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How Far Away One Can Penetrate with Gaia in Star Cluster Studies? How far away we can penetrate with Gaia in star clusters study? D.A.Kovaleva, INASAN, Moscow, Russia N.V.Kharchenko, MAO, Kiev, Ukraine A.E.Piskunov, INASAN, Moscow, Russia S. Röser, LSW-ARI, Heidelberg, Germany E. Schilbach, LSW-ARI, Heidelberg, Germany S.Yen, LSW, Heidelberg, Germany SFB 881 Workshop Heidelberg 15-17 Aug 2018 Clusters: MWSC Globular (logt>9.8) Young (logt≤7.3) in the Other (logt>7.3) Milky Way MWSC includes 3210 clusters of different types among them: associations 51 globular clusters 147 moving groups 19 embedded/with nebula 132 remnant clusters 401 members 0.8 mln All having ages, masses, distances and other parameters d <10 kpc dmod 2.4 kpc εd/d ~11% R.Hurt, Spitzer Science Center SFB 881 Workshop Heidelberg 15-17 Aug 2018 2 R.Hurt, Spitzer Science Center Gaia DR1 (TGAS) stars with trigonometric parallaxes 휛 2 mln. ε휛 0.3-0.7 mas G_lim 12 mag available since Sept 2016 Kovaleva, Dana A.; Piskunov, Anatoly E.; Kharchenko, Nina V.; Röser, Siegfried; Schilbach, Elena; Scholz, Ralf- Dieter; Reffert, Sabine; Yen, Steffi X. “Open star clusters in the Milky Way. Comparison of photometric and trigonometric distance scales based on Gaia TGAS data” 2017A&A...606L...8K 66 clusters with 16+ MWSC 60%-members in TGAS SFB 881 Workshop Heidelberg 15-17 Aug 2018 3 Gaia DR2 stars with trigonometric parallaxes 휛 1.3 bln. ε휛 0.007-0.6 mas G_lim >20 mag (not in all area) available since Apr 2018 + proper motions + two-color photometry G_BP, G_RP + radial velocities for 7.2 mln. stars - A breakthrough in cluster studies is expected. - A number of works having in mind, in particular, re-obtain parameters of the clusters with Gaia DR2: • Cantat-Gaudin, T., et al. “A Gaia DR2 view of the Open Cluster population in the Milky Way” 2018arXiv180508726C • Yalyalieva, L. N., et al. “A comprehensive study of 94 open clusters based on the data from IPHAS, GAIA DR2, and other sky surveys” 2018arXiv180703391Y • Castro-Ginard, A.; et al. “A new method for unveiling Open Clusters in Gaia: new nearby Open Clusters confirmed by DR2” 2018arXiv180503045C • …… • Yen S. et al. “Deriving open cluster parameters using Gaia”, present meeting SFB 881 Workshop Heidelberg 15-17 Aug 2018 4 Parallax Gaia DR2 vs G magnitude for 60% members of MWSC clusters: previouos approach is of no use MWSC 3779=NGC 7789 d(MWSC)=1800 pc MWSC 2967 = IC 4756 d(MWSC)=483 pc TGAS Foreground MWSC 821=Platais 6 Cluster d(MWSC)=347 pc members Background stars MWSC 1308=NGC 2451A d(MWSC)=188 pc Mean trigonometric parallax of a cluster is valid if we calculate it based on reliable members only. Selection of members should be SFB 881 Workshop Heidelberg 15-17 Aug 2018 re-done. 5 Primary purposes of this study: (1)to compare open cluster photometric distance scale based on our determinations of star cluster parameters we have derived within the MWSC project with the trigonometric parallaxes from Gaia DR2 catalogue; (2)to establish a degree and extent of conformance of both scales. To achieve these purposes, one needs to select only reliable cluster members based on new data. SFB 881 Workshop Heidelberg 15-17 Aug 2018 6 What we use Data: • Gaia DR2 stars in the area of MWSC open clusters (RA, Dec, r2+δr) – ퟏퟎퟑ − ퟏퟎퟔ stars per cluster • We start with open clusters used in TGAS-MWSC comparison, and then probe more and more distant ones. Instruments: STILTS, TOPCAT, visual inspection Diagrams: G-parallax, VPD, CMD (G-G_RP) – G, RA-Dec Distributions: pm_RA, pm_Dec, parallax 휛(Gaia DR2), Rv Filters: G<18 magnitude cut (χퟐ cut) & flux excess cut (Lindegren et al. 2018); CMD outliers, parallax outliers Comparison: MWSC data: d 흕 푴푾푺푪 [풎풂풔] = ퟏퟎퟎퟎ/풅[풑풄] (photometric parallax) vs Gaia DR2 averaged parallax <휛(Gaia DR2)> SFB 881 Workshop Heidelberg 15-17 Aug 2018 7 Task: to select reliable members of clusters based on Gaia DR2 data • Not necessarily all members, quality here is more important than number SFB 881 Workshop Heidelberg 15-17 Aug 2018 8 MWSC 105 (NGC 381) as example: Proper Propermotion lg 휛 - G_mag motion Though diagrams lg 휛 – G mag do not represent stars with negative parallaxes, these stars are included in all calculations. SFB 881 Workshop Heidelberg 15-17 Aug 2018 9 Selecting reliable members 1: VPD SFB 881 Workshop Heidelberg 15-17 Aug 2018 10 Checking reliable members 2 SFB 881 Workshop Heidelberg 15-17 Aug 2018 11 Filtering reliable members by quality of parameters Dark blue dots – magnitude cut, flux excess cut applied < 휛 >=0.836 mas sd = 0.080 mas N_rm=129 휛(MWSC)= 0.833 mas SFB 881 Workshop Heidelberg 15-17 Aug 2018 12 Avoiding false clusters: checking different parameters and relations. Blanco 1 MWSC 7 = Blanco 1 Not a cluster SFB 881 Workshop Heidelberg 15-17 Aug 2018 13 Avoiding false clusters: checking different parameters and relations. Stock 2. I MWSC 173 = Stock 2 Another cluster? SFB 881 Workshop Heidelberg 15-17 Aug 2018 14 Avoiding false clusters: checking different parameters and relations. Stock 2. II A parallax concentration corresponds a pmRA – pmDec concentration… MWSC 173 However CMD shows it is NOT a cluster, after all SFB 881 Workshop Heidelberg 15-17 Aug 2018 15 Moving farther away MWSC 137 = NGC 654 SFB 881 Workshop Heidelberg 15-17 Aug 2018 16 < 휛 >=0.306 mas sd = 0.070 mas N_rm=296 휛(MWSC)=0.560 mas SFB 881 Workshop Heidelberg 15-17 Aug 2018 17 Still farther away MWSC 1032 = Berkeley 31 < 휛 >=0.154 mas sd = 0.16 mas N_rm=70 휛(MWSC)=0.16 mas SFB 881 Workshop Heidelberg 15-17 Aug 2018 18 Intermediate results: all clusters from the TGAS-MWSC list + a set of remote clusters + systematic processing started SFB 881 Workshop Heidelberg 15-17 Aug 2018 19 Intermediate results – mean trigonometric parallax vs MWSC photometric parallax 휛[mas]=1000/d[pc] 240 MWSC clusters processed, for 143 < 휛(퐺푎푖푎 퐷푅2) > obtained. All clusters from the TGAS-MWSC list are processed. The size of circles represents the number of reliable members used for averaging. SFB 881 Workshop Heidelberg 15-17 Aug 2018 20 Intermediate results – is there a systematic offset? < 휛 퐺푎푖푎 퐷푅2 − 휛(푀푊푆퐶)> = -0.052±0.013 mas Gaia general negative offset = -0.029 mas SFB 881 Workshop Heidelberg 15-17 Aug 2018 21 Comparison with results of other authors Yalyalieva, L. N., et al. “A comprehensive study of 94 open clusters based on the data from IPHAS, GAIA DR2, and other sky surveys” 2018arXiv180703391Y MWSC 35 = King 1 Gaia DR2 cluster parallaxes Photometric parallaxes MWSC 165 = SAI 16 solution atypical in Yal2018 SFB 881 Workshop Heidelberg 15-17 Aug 2018 22 Possible cause of discrepancies: known clusters overlap MWSC 180 = ASCC 8 (green, main host) MWSC 173 = Stock 2 (blue, invader) SFB 881 Workshop Heidelberg 15-17 Aug 2018 23 More examples of overlapping clusters MWSC 3604 = King 9 , main host (blue) MWSC 3603 = NGC 7245, invader (green) Distributions of parallaxes SFB 881 Workshop Heidelberg 15-17 Aug 2018 24 Resume 1. Purpose: to check the degree and extent of agreement between photometric and trigonometric scales of distance. 2. Data: photometric parallaxes obtained from MWSC distances to open clusters, and averaged Gaia DR2 trigonometric parallaxes of reliable members of these clusters. 3. Procedure of selection of reliable cluster members: based on Gaia DR2 data, preliminary information from MWSC concerning coordinates and angular radius of a cluster. 4. Applied so far to 240 open clusters, including all members of the TGAS- MWSC list. Reliable members selected, parallaxes and proper motions are uniformly obtained for 143 of them. The scales agree reasonably well to the distance of 8 kpc. The work is going on. 5. Gaia DR2 data allow to separate members of different clusters localized in the same field of view, in a number of cases which require additional investigation. SFB 881 Workshop Heidelberg 15-17 Aug 2018 27 Acknowledgements We are grateful to S. Reffert and R.-D. Scholz for the collaboration, and to A. Just for the interest and useful suggestions . DK thanks the SFB 881 and the Workshop organizing committee for the opportunity to participate the event. DK is thankful for participation in Gaia Data Workshop in Heidelberg (June 2018), also supported by SFB 881, which greatly promoted this investigation. The extensive use of TOPCAT http://www.starlink.ac.uk/topcat/ and STILTS http://www.starlink.ac.uk/stilts/ packages is gratefully acknowledged. SFB 881 Workshop Heidelberg 15-17 Aug 2018 28 .
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