Astrometric Membership Tests for the Zinn-Newell-Gibson "UV-Bright" Stars in Galactic Globular Clusters
aa r X i v : . [ a s t r o - ph . S R ] F e b Draft version February 19, 2021
Typeset using L A TEX twocolumn style in AASTeX62
Astrometric Membership Tests for the Zinn–Newell–Gibson“UV-Bright” Stars in Galactic Globular Clusters
Howard E. Bond
1, 2,3 Department of Astronomy & Astrophysics, Pennsylvania State University, University Park, PA 16802, USA Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Visiting Astronomer, Cerro Tololo Inter-American Observatory and Kitt Peak National Observatory, National Optical AstronomyObservatory, operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the NationalScience Foundation.
ABSTRACTIn 1972, Zinn, Newell, & Gibson (ZNG) published a list of 156 candidate “UV-bright” stars theyhad found in 27 Galactic globular clusters (GCs), based on photographs in the U and V bands.UV-bright stars lie above the horizontal branch (HB) and blueward of the asymptotic-giant branch(AGB) and red-giant branch in the clusters’ color-magnitude diagrams. They are in rapid evolutionaryphases—if they are members and not unrelated bright foreground stars. The ZNG list has inspirednumerous follow-up studies, aimed at understanding late stages of stellar evolution. However, the ZNGcandidates were presented only in finding charts, and celestial coordinates were not given. Using myown collection of CCD frames in u and V , I have identified all of the ZNG objects, and have assembledtheir coordinates, parallaxes, and proper motions from the recent Gaia
Early Data Release 3 (EDR3).Based on the
Gaia astrometry, I have determined which objects are probable cluster members (45%of the sample). For the members, using photometry from EDR3, I have assigned the stars to variousevolutionary stages, including luminous post-AGB stars, and stars above the HB. I point out severalZNG stars of special interest that have still, to my knowledge, never been studied in detail. This studyis an adjunct to a forthcoming survey of the Galactic GCs in the uBVI photometric system, designedfor detection of low-gravity stars with large Balmer discontinuities.
Keywords: stars: AGB and post-AGB — globular clusters — stars: evolution — post-horizontal-branchstellar evolution STARS ABOVE THE HORIZONTAL BRANCHIN GLOBULAR CLUSTERSIn color-magnitude diagrams (CMDs) of globular clus-ters (GCs), the vast majority of stars in post-main-sequence evolutionary stages lie on the subgiant branch,red-giant branch (RGB), horizontal branch (HB), andasymptotic-giant branch (AGB). There are, however,rare stars in transient phases of rapid evolution thatlie above the HB and to the blue of the AGB/RGB incluster CMDs. These objects include stars that have de-parted the HB and are evolving toward the AGB, post-HB stars that reached the AGB but then left it beforearriving at the AGB tip (post-early-AGB, or PEAGB,stars), and objects that reached the tip of the AGB and
Corresponding author: Howard E. [email protected] are now evolving rapidly toward higher temperatures(post-AGB, or PAGB, stars). See Moehler et al. (2019,hereafter M+19; their Figure 7) for examples of theo-retical post-HB evolutionary tracks that produce starsabove the HB in GC CMDs. It is also possible thatbinary interactions can generate stars lying above theHB.Our group at Pennsylvania State University is con-ducting an observational survey aimed at creating acomplete census of above-horizontal-branch (AHB) starsin the Galactic GC system. This survey is based on pho-tometry in the uBVI system (Bond 2005), which is op-timized for detection of low-gravity evolved stars withlarge Balmer discontinuities in their spectral-energydistributions. With astrometry from
Gaia now avail-able, including the recent Early Data Release 3 (EDR3;Gaia Collaboration et al. 2020), we can further testcluster membership using precise parallaxes and proper
Bond motions (PMs). Our uBVI work led to discoveries of lu-minous “yellow” PAGB stars in M79 (Bond et al. 2016,hereafter BCS16) and M19 (Bond et al. 2021, hereafterB+21). In the case of M19, we also discovered a hotter,and equally luminous, blue PAGB star belonging to thecluster. Full details of our uBVI survey for AHB starswill be presented in a forthcoming paper (Davis et al.2021, hereafter D+21). Subsequent publications willexplore the utility of yellow PAGB stars—which are thevisually brightest stars in old populations—as standardcandles for determining extragalactic distances, as Ihave advocated (Bond 1997a,b). THE ZINN-NEWELL-GIBSON “UV-BRIGHT”STARSThe two luminous PAGB stars that B+21 found inM19 are among the brightest and most conspicuousmembers known in any GC. In spite of this, they hadnot, to our knowledge, been recognized as cluster mem-bers by previous investigators of this massive GC. How-ever, when we researched the literature, we found thatboth of the M19 objects had been identified as “UV-bright” candidates in the classical survey of Zinn et al.(1972, hereafter ZNG).The ZNG team had blinked photographs of 27 GCsobtained in the U and V bands, and had identified 156candidates that were the brightest objects in the clus-ters in the U band. The term “UV-bright” was a bitof a misnomer. Many of the ZNG objects are indeedhot post-AGB stars, including the prototypical luminousblue stars Barnard 29 in M13, and von Zeipel 1128 inM3. However, many other ZNG candidates are evencooler than the yellow Type II Cepheids in GCs, butnevertheless brighter than most of the cluster membersin the U band—including objects that are actually un-related bright foreground stars.ZNG presented finding charts for their candidates,but did not provide celestial coordinates. There havebeen several follow-up studies of individual ZNG ob-jects (e.g., Zinn 1974; Harris et al. 1983; de Boer 1985;Jasniewicz et al. 2004; Moehler 2001, 2010; M+19; andreferences therein), and several of these stars haveproven to be of great astrophysical interest. These in-clude, for example, several now well-known hot PAGBstars (see the lists in M+19). However, there has never,to my knowledge, been a published list of the celestialcoordinates of all of the ZNG stars.As an adjunct to the D+21 study, I determined thecoordinates of all of the ZNG stars, and I present themhere. I then used astrometry from Gaia
EDR3 to testthe cluster memberships of the candidates. Lastly, I givean indication of the evolutionary status of the stars that appear to be cluster members, based on their locationsin the CMDs, and I point out several unstudied objectsof interest. IDENTIFYING THE ZNG STARSI first identified each ZNG star in my uBVI
CCD GCsurvey CCD images. These frames had been obtainedwith 0.9-, 1.5-, and 4-m telescopes at Kitt Peak NationalObservatory and Cerro Tololo Inter-American Observa-tory; they are described in detail by B+21 and D+21. Iblinked the u and V frames, while comparing them withthe ZNG finding charts. In nearly every case, the starswere identified unambiguously; only a handful of objectsnear the cluster centers were less certain. Approximatecoordinates were then determined using images from theSpace Telescope Science Institute Digitized Sky Survey, images from the PanSTARRS-1 sky survey, and/or ina few cases images from the Hubble Space Telescope . With all of these tools, coordinates can be obtained byplacing a cursor on the stellar images.Finally, I identified each object in the
Gaia
EDR3 cat-alog. Table 1 lists the 156 ZNG candidates, along withtheir J2000 coordinates,
Gaia parallaxes and PMs, andthe
Gaia apparent G magnitudes and BP − RP col-ors. The notes to the table give information on the fewinstances of uncertain identifications, as well as otherinformation on the objects, but are not intended to bea complete literature survey. CLUSTER MEMBERSHIP TESTSUsing the EDR3 astrometry, I tested each ZNG candi-date for cluster membership. Two criteria were appliedto each star: PM and parallax; and in a few instances athird one: radial velocity (RV). First, I determined themean PMs of each cluster in right ascension and declina-tion and their dispersions, based on a selection of clustermembers from the EDR3 catalog; then I required thateach candidate have a PM consistent with that of thehost cluster. In a large majority of cases, the PM cri-terion alone was sufficient to exclude the non-members.Next the parallax was considered. I adopted a nominalparallax for each cluster, based on the reciprocals of thedistances given in the Harris (2010, hereafter H10) cat-alog of cluster parameters. The parallax of each can-didate was generally required to be consistent, within https://archive.stsci.edu/cgi-bin/dss form https://ps1images.stsci.edu/ https://hla.stsci.edu/hlaview.html https://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=I/350/gaiaedr3 ∼ harris/mwgc.dat. Basedon the discussion in Gaia Collaboration et al. (2018), I used the he ZNG Catalog of UV-Bright Stars
33 times its stated uncertainty, with the nominal clusterparallax. There was, however, a handful of cases wherethe star’s PM was in accord with membership, but theparallax was larger (or occasionally smaller) than thatof the cluster, by more than the nominal 3 times theuncertainty. It is plausible that their EDR3 parallaxesmay have been affected by source crowding. These am-biguous cases are discussed in the notes to Table 1. Fi-nally, in a handful of instances for the brightest objects,EDR3 also gives a radial velocity (RV), another valuablemembership criterion via comparison with the cluster’sRV given in H10. The few cases where the
Gaia
RVhelped confirm membership are indicated in the notesto Table 1.Figure 1 illustrates the PM and parallax membershiptests, for the case of the cluster M22. I selected starsfrom
Gaia
EDR3 lying within 5 ′ of the cluster center,and brighter than G magnitude 13. The PMs of thesestars are plotted as black and red points: black for starswith a parallax less than 0.6 mas (which is about twicethe nominal cluster parallax), and red for the few starswith a parallax of more than 0.6 mas (likely foregroundstars). The EDR3 PMs are so precise that the clustermembers form a tight distribution. The small numberof field stars and foreground objects have a much widerdispersion and are offset from the cluster mean.The larger filled circles in Figure 1 plot the PMs of 16of the 18 ZNG candidates. (Two of them have PMs solarge they are outside the frame.) The ZNG stars plot-ted in blue have parallaxes less than 0.6 mas, and theones with larger parallaxes are plotted in green. Fourof the ZNG objects have PMs consistent with clustermemberships, as well as small parallax values, makingthem highly probable members. One of them, as notedin Table 1, also has a RV consistent with membership.The remaining ZNG candidates in the figure have PMsclearly inconsistent with that of the cluster, and most ofthem also have parallaxes too large for cluster member-ship. The final membership classifications are given in col-umn 10 of Table 1, with a question mark for the fewambiguous cases; these are discussed in the notes to thetable.
H10 cluster distances rather than distances based directly on
Gaia parallaxes; in any case, this choice makes little difference inthe membership tests. There is always a small possibility of a field star happeningto have a similar parallax and PM to that of the cluster, espe-cially in cases of a cluster with a small PM superposed on a richfield; we will give a detailed and more formal discussion of cluster-membership probability estimation in D+21.
Figure 1.
Gaia
EDR3 proper motions for stars lying within 5 ′ ofthe center of the globular cluster M22. The small points plot starsbrighter than G = 13; black points are for stars with a parallax lessthan 0.6 mas, and red points for stars with larger parallaxes. Theproper motions for 16 of the ZNG stars are plotted as large filledcircles, colored blue for parallaxes less than 0.6 mas, and green forlarger parallaxes. Two of the ZNG candidates have large propermotions placing them outside the frame. Four of the ZNG starshave both proper motions and parallaxes consistent with clustermembership. EVOLUTIONARY STATUSFor the ZNG candidates that I considered to be likelycluster members, I estimated their evolutionary statusesbased on their locations in the cluster CMDs. Theclassification scheme that I adopted is based on clus-ter CMDs in which the
Gaia apparent magnitude G isplotted against the color index BP − RP . Figure 2 pro-vides examples. Here the Gaia data are presented forthree ZNG GCs: M13, M53, and NGC 5897. Also in-cluded is M79, which is not one of the ZNG clusters,but contains the luminous yellow PAGB star discoveredby BCS16. All four clusters are only lightly reddened[ E ( B − V ) = 0 .
02, 0.02, 0.09, and 0.01, respectively,from H10]. For each cluster, I selected a sample of likelymembers from the EDR3 catalog, with parallaxes andPMs consistent with membership.In each panel in Figure 2, the region of the CMDabove the HB and to the blue of the AGB is dividedschematically into several boxes. These are based onpost-HB evolutionary tracks, such as those in M+19.The luminous PAGB sequence is divided on the ba-sis of color into red, yellow, blue, and violet objects—rPAGB, yPAGB, bPAGB, and vPAGB, respectively.The rPAGB stars have unreddened BP − RP colors ly- Bond
Figure 2.
Examples of a schematic classification scheme for stars above the horizontal branch in globular clusters, based on color-magnitude diagrams plotting the
Gaia G magnitude versus BP − RP color. The black filled circles in each frame show Gaia photometryfor members of four lightly reddened clusters. The members were selected on the basis of
Gaia
EDR3 parallaxes and proper motions.The clusters’ horizontal branch (HB), red-giant branch (RGB), and asymptotic giant branch (AGB) are labeled. The brightest stars areclassified as post-AGB stars with red (rPAGB), yellow (yPAGB), blue (bPAGB), and violet (vPAGB) colors. Stars fainter than the PAGBsequence, down to within 0.5 mag of the HB or AGB, are classified as AHB objects; these are stars evolving off the HB toward coolertemperatures, along with stars leaving the AGB and evolving back to hotter temperatures. The hottest and optically faintest objects at thelower left are a combination of vPAGB stars and AGB-manqu´e stars. See the text for further discussion of the scheme. The classificationgrid is shifted in color and magnitude according to the reddening and distance of each cluster. Upper left: M13. Filled colored circles markthe vPAGB star ZNG 1 = Barnard 29, and four AHB stars (ZNG 3, 4, 6, and 7). Upper right: M53. Filled colored circles mark two AHBstars (ZNG 3 and 4), two stars on the RGB (ZNG 6 and 9), three stars on the AGB (ZNG 7, 8, and 13), and one star on the HB (ZNG 16).Lower left: NGC 5897. A filled colored circle marks the rPAGB star ZNG 2. Lower right: M79. This cluster is not in the ZNG list, but isincluded to illustrate its luminous yellow PAGB star, discovered by BCS16. ing between 0.8 and up to within 0.1 mag of the AGB,and G magnitudes at least 3.5 mag brighter than thatof the HB at BP − RP = 0 .
8. The yPAGB stars have0 < ( BP − RP ) < .
8, and lie at least 3.5 mag brighterthan the HB at the same color. bPAGB objects arein the color range − . < ( BP − RP ) <
0, and areat least 3.5 mag brighter than the HB at the samecolor. The hottest PAGB stars are those bluer than BP − RP = − .
25, and either brighter than the bright-ness of the HB at a color of zero (vPAGB), or fainter (vPAGB/AGB manqu´e). AGB-manqu´e objects evolvedirectly from the extremely blue HB to the white-dwarf(WD) sequence, without ever becoming cool stars. Asit happens, however, the ZNG sample does not containany such stars. These divisions are somewhat arbitrary,but give a useful indication of the approximate temper-atures. The scheme should be considered preliminary,and will be revised in our forthcoming paper (D+21).Stars lying below the PAGB sequence, but at least0.5 mag above the HB or AGB, are called AHB objects. he ZNG Catalog of UV-Bright Stars RESULTSUsing the plotting tools at Vizier (see footnote 4) togenerate CMDs derived from
Gaia
EDR3 data for eachGC, I applied the classification scheme described aboveto all of the ZNG objects. The classification grid wasshifted in color and magnitude according to the red-dening and distance of each cluster. The classificationresults are given in column 11 of Table 1.Out of the 156 candidates, 86 (55%) are non-membersor likely non-members, nearly all of them bright starsthat clearly lie in the cluster foregrounds. AlthoughZNG excluded stars known to be variable at the timeof their survey, the list contains several objects sub-sequently found to vary. These include two Type IICepheids and, more surprisingly, ten RR Lyrae vari-ables. I speculate that the latter were selected by ZNGbecause they happened to be near maximum light at theepoch of the U -band exposures.There are several cases of objects that are blends oftwo or more stars, which would account for them appear-ing unusually bright in ground-based images. More sur-prising is that there are quite a few candidates that ap-pear to be unexceptional stars lying on the RGB, AGB,or HB sequences. However, a few of them are of in-terest because they are extremely bright, lying close tothe tips of the RGB or AGB. One of the most remark-able of these is NGC 6712 ZNG 4, a very luminous starat the cluster’s AGB tip; it is the known Mira variableAP Sct, which is NGC 6712 V2 in the Clement et al.(2001) catalog of variable stars in GCs. One blue ob-ject, NGC 6093 (M80) ZNG 3, lies close to the positionof a known X-ray source, CX 3.Among the bright PAGB stars, there are two redPAGB (rPAGB) objects: NGC 5897 ZNG 2 andNGC 6626 (M28) ZNG 5. The former star has not,to my knowledge, been recognized previously as a lu-minous PAGB star; the latter is a known RV Taurivariable, as described in the notes to Table 1. Thereis only one yellow PAGB (yPAGB) star, the one in thecluster M19 that was recently pointed out for the firsttime by B+21.The table contains six luminous blue PAGB (bPAGB)and two violet PAGB (vPAGB) stars. Of these, severalare already well known (see M+19): NGC 5272 (M3) ∼ cclement/cat/listngc.html ZNG 1 (von Zeipel 1128), NGC 6205 (M13) ZNG 1(Barnard 29), NGC 6254 (M10) ZNG 1, NGC 6712ZNG 1, and NGC 6779 (M56) ZNG 2. The bPAGBstar NGC 6273 (M19) ZNG 2 was only noted for thefirst time in the recent B+21 study. NGC 6402 (M14)ZNG 1 was identified as a hot PAGB star based on
GALEX imaging by Schiavon et al. (2012), but has nototherwise been studied. The bPAGB object NGC 6333(M9) ZNG 1 has not, to my knowledge, been recognizedpreviously.Lastly, Table 1 contains 27 AHB objects. As notedabove, these are likely to be a mixture of stars evolvingoff the hot HB toward the AGB, and stars that reachedthe AGB and are now evolving back toward higher effec-tive temperatures. Like the PAGB stars, they are worthfurther study.The ZNG survey was an important early observationalinvestigation that added to our understanding of latestellar evolution. Even after nearly five decades, thereare still unexplored objects of considerable interest inthe ZNG catalog. Our group’s uBVI survey, to be re-ported by B+21, will follow in the path illuminated bythis classical investigation.I thank the Penn State “post-AGB group”— RobinCiardullo, Brian Davis, and Michael Siegel—for discus-sions of evolved stars in globular clusters.My uBVI observations were partially supported byNASA grant NAG 5-6821 under the “UV, Visible, andGravitational Astrophysics Research and Analysis” pro-gram, and by the Director’s Discretionary ResearchFund at STScI. I also thank the staffs at Cerro Tololoand Kitt Peak for their support over many years.This research has made use of the VizieR cata-logue access tool, CDS, Strasbourg, France (DOI:10.26093/cds/vizier). The original description of theVizieR service was published by Ochsenbein et al.(2000).This work has made use of data from the EuropeanSpace Agency (ESA) mission
Gaia
Gaia
Gaia
Multilateral Agreement.The Digitized Sky Surveys were produced at theSpace Telescope Science Institute under U.S. Govern-ment grant NAG W-2166. The images of these sur-veys are based on photographic data obtained using theOschin Schmidt Telescope on Palomar Mountain and theUK Schmidt Telescope. The plates were processed into
Bond the present compressed digital form with the permissionof these institutions.The Pan-STARRS1 Surveys (PS1) and the PS1 publicscience archive have been made possible through contri-butions by the Institute for Astronomy, the Universityof Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the MaxPlanck Institute for Astronomy, Heidelberg and the MaxPlanck Institute for Extraterrestrial Physics, Garching,The Johns Hopkins University, Durham University, theUniversity of Edinburgh, the Queen’s University Belfast,the Harvard-Smithsonian Center for Astrophysics, theLas Cumbres Observatory Global Telescope NetworkIncorporated, the National Central University of Tai-wan, the Space Telescope Science Institute, the NationalAeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Di-vision of the NASA Science Mission Directorate, theNational Science Foundation Grant No. AST-1238877,the University of Maryland, Eotvos Lorand University(ELTE), the Los Alamos National Laboratory, and theGordon and Betty Moore Foundation.Based in part on observations made with the NASA/ESA
Hubble Space Telescope , obtained from the dataarchive at the Space Telescope Science Institute. STScIis operated by the Association of Universities for Re-search in Astronomy, Inc. under NASA contract NAS5-26555.
Facilities:
CTIO 0.9m, 1.5m; KPNO 0.9m, 4m;Gaia, Swift, HSTREFERENCES
Ambika, S., Parthasarathy, M., Aoki, W., et al. 2004, A&A,417, 293Boberg, O. M., Friel, E. D., & Vesperini, E. 2016, ApJ, 824,5Bond, H. E. 1997a, in IAU Symp. 180, Planetary Nebulae,ed. H. J. Habing & H. J. G. L. M. Lamers (Dordrecht:Kluwer), 460Bond, H. E. 1997b, in The Extragalactic Distance Scale, ed.M. Livio, M. Donahue, & N. Panagia (Cambridge:Cambridge Univ. Press), 224Bond, H. E. 2005, AJ, 129, 2914Bond, H. E., Ciardullo, R., & Siegel, M. H. 2016, AJ, 151,40 (BCS16)Bond, H. E., Davis, B. D., Siegel, M. H., et al. 2021, AJ,161, 125 (B+21)Clement, C. M., Muzzin, A., Dufton, Q., et al. 2001, AJ,122, 2587Clement, C. C., & Sawyer Hogg, H. 1978, AJ, 83, 167Clementini, G., Ripepi, V., Molinaro, R., et al. 2019, A&A,622, A60Contreras Pe˜na, C., Catelan, M., Grundahl, F., et al. 2018,AJ, 155, 116Davis, B. D., Bond, H. E., Siegel, M. H., & Ciardullo, R.2021, in preparation (D+21)de Boer, K. S. 1985, A&A, 142, 321Deras, D., Arellano Ferro, A., L´azaro, C., et al. 2019,MNRAS, 486, 2791Gaia Collaboration, Brown, A. G. A., Vallenari, A., et al.2020, arXiv:2012.01533Gaia Collaboration, Helmi, A., van Leeuwen, F., et al.2018, A&A, 616, A12 Gebhardt, K., Pryor, C., Williams, T. B., et al. 1997, AJ,113, 1026Geier, S., Raddi, R., Gentile Fusillo, N. P., et al. 2019,A&A, 621, A38Harris, W. E. 2010, arXiv:1012.3224 (H10)Harris, H. C., Nemec, J. M., & Hesser, J. E. 1983, PASP,95, 256Heinke, C. O., Grindlay, J. E., Edmonds, P. D., et al. 2003,ApJ, 598, 516Jasniewicz, G., de Laverny, P., Parthasarathy, M., et al.2004, A&A, 423, 353Moehler, S. 2001, PASP, 113, 1162Moehler, S. 2010, Mem. Soc. Astron. Italiana, 81, 838Moehler, S., Landsman, W. B., Lanz, T., et al. 2019, A&A,627, A34 (M+19)Ochsenbein, F., Bauer, P., & Marcout, J. 2000, A&AS, 143,23Roederer, I. U. & Sneden, C. 2011, AJ, 142, 22Safonova, M., Mkrtichian, D., Hasan, P., et al. 2016, AJ,151, 27Schaeuble, M., Preston, G., Sneden, C., et al. 2015, AJ,149, 204Schiavon, R. P., Dalessandro, E., Sohn, S. T., et al. 2012,AJ, 143, 121Servillat, M., Webb, N. A., Lewis, F., et al. 2011, ApJ, 733,106Shetrone, M., Martell, S. L., Wilkerson, R., et al. 2010, AJ,140, 1119Zinn, R. 1974, ApJ, 193, 593Zinn, R. J., Newell, E. B., & Gibson, J. B. 1972, A&A, 18,390 (ZNG) he ZNG Catalog of UV-Bright Stars Table 1 . The ZNG UV-Bright Candidates and
Gaia
Astrometry and Photometry
Cluster ZNG RA Dec Parallax µα µδ G BP − RP Cluster Classi- RemarkscNGC/M No. [J2000] [J2000] [mas] [mas yr −
1] [mas yr −
1] [mag] [mag] Member?a ficationb2419 1 07 38 11.156 +38 52 27.74 0 . ± . . ± . − . ± .
036 16.318 0 .
987 no2 07 38 09.234 +38 53 12.77 0 . ± . − . ± . − . ± .
090 17.395 0 .
305 yes AHB4147 1 12 09 58.479 +18 34 08.78 1 . ± . − . ± . − . ± .
023 14.326 0 .
823 no2 12 10 05.661 +18 32 45.69 0 . ± . − . ± . − . ± .
099 16.856 0 .
250 yes HB 14590/ 1 12 39 40.099 −
26 43 02.62 0 . ± . − . ± . − . ± .
021 14.300 0 .
498 noM68 2 12 39 22.513 −
26 45 11.87 0 . ± . − . ± .
016 1 . ± .
012 12.258 1 .
451 yes AGB 25024/ 1 13 12 56.879 +18 10 53.17 4 . ± . − . ± . − . ± .
016 12.388 1 .
013 noM53 2 13 12 47.541 +18 10 23.15 1 . ± . − . ± . − . ± .
024 14.395 0 .
903 no3 13 12 45.206 +18 11 57.44 0 . ± . − . ± . − . ± .
033 14.850 0 .
192 yes AHB 34 13 12 47.406 +18 07 10.77 0 . ± . − . ± . − . ± .
062 15.701 0 .
297 yes AHB5 13 13 09.478 +18 10 58.70 0 . ± . − . ± . − . ± .
031 14.741 0 .
770 no6 13 13 11.459 +18 08 09.47 0 . ± . − . ± . − . ± .
047 15.734 1 .
136 yes RGB7 13 12 48.140 +18 09 45.71 − . ± . − . ± . − . ± .
100 15.129 1 .
133 yes? AGB 48 13 13 02.930 +18 11 06.60 − . ± . − . ± . − . ± .
125 14.015 1 .
332 yes AGB 59 13 13 03.347 +18 11 43.51 0 . ± . − . ± . − . ± .
029 14.613 1 .
292 yes RGB 610 13 13 11.209 +18 13 08.27 1 . ± . . ± . − . ± .
031 14.764 0 .
808 no11 13 12 29.048 +18 07 16.08 1 . ± . − . ± .
024 10 . ± .
025 14.137 0 .
776 no12 13 13 22.626 +18 10 09.39 1 . ± . . ± . − . ± .
048 14.872 0 .
842 no13 13 12 57.021 +18 10 34.92 − . ± . − . ± . − . ± .
100 14.309 1 .
177 yes AGB14 13 12 54.119 +18 09 56.99 0 . ± . . ± . − . ± .
376 13.968 1 .
111 no? 715 13 12 58.238 +18 08 36.84 2 . ± . . ± . − . ± .
313 15.881 0 .
802 no16 13 12 54.235 +18 11 47.54 − . ± . − . ± . − . ± .
101 16.995 0 .
197 yes HB5053 1 13 16 39.651 +17 41 39.43 1 . ± . − . ± .
025 4 . ± .
026 14.461 0 .
923 no2 13 16 08.506 +17 41 43.35 1 . ± . − . ± . − . ± .
027 14.411 0 .
821 no5272/ 1 13 42 16.750 +28 26 00.61 0 . ± . − . ± . − . ± .
028 14.947 − .
442 yes vPAGB 8M3 2 13 42 10.767 +28 19 05.32 1 . ± . − . ± .
018 5 . ± .
010 13.343 0 .
859 no3 13 42 23.099 +28 25 00.53 0 . ± . − . ± . − . ± .
025 15.621 0 .
637 yes HB 94 13 42 17.042 +28 23 02.81 0 . ± . − . ± . − . ± .
118 15.616 0 .
669 yes HB 105 13 42 18.924 +28 19 34.11 0 . ± . − . ± . − . ± .
024 15.657 0 .
551 yes HB 116 13 41 51.504 +28 17 44.54 0 . ± . − . ± . − . ± .
012 13.931 0 .
813 no5466 1 14 05 10.675 +28 28 54.23 0 . ± . . ± . − . ± .
022 13.861 0 .
592 no2 14 05 15.075 +28 26 52.20 1 . ± . . ± . − . ± .
016 13.987 0 .
874 no3 14 05 16.967 +28 25 46.55 1 . ± . − . ± . − . ± .
014 13.867 0 .
719 no4 14 05 38.767 +28 33 00.05 0 . ± . . ± . − . ± .
017 14.060 0 .
818 no5 14 05 41.566 +28 34 37.32 − . ± . − . ± . − . ± .
075 17.410 − .
144 yes HB 126 14 05 29.091 +28 32 47.23 0 . ± . − . ± . − . ± .
016 14.188 1 .
139 yes AGB 135634 1 14 29 36.219 −
05 58 16.76 0 . ± . . ± . − . ± .
042 15.650 0 .
762 no2 14 29 33.211 −
05 57 45.36 0 . ± . − . ± . − . ± .
019 14.080 1 .
030 no3 14 29 29.487 −
05 58 44.27 0 . ± . − . ± . − . ± .
021 13.988 0 .
828 no5897 1 15 17 17.592 −
21 03 18.75 0 . ± . − . ± . − . ± .
014 13.330 0 .
961 no2 15 17 30.443 −
21 00 10.37 0 . ± . − . ± . − . ± .
016 12.672 1 .
378 yes rPAGB 145904/ 1 15 18 31.167 +02 05 00.74 0 . ± . . ± . − . ± .
050 14.164 1 .
096 no? 15M5 2 15 18 35.690 +02 03 46.11 − . ± . . ± . − . ± .
038 11.562 1 .
705 no? 163 15 18 17.349 +02 02 29.55 1 . ± . − . ± . − . ± .
054 13.317 0 .
874 no4 15 18 48.160 +02 02 16.81 1 . ± . − . ± .
019 17 . ± .
021 13.422 0 .
846 no5 15 18 45.927 +02 04 14.90 1 . ± . − . ± . − . ± .
024 13.776 0 .
811 no6 15 18 35.026 +02 08 40.09 0 . ± . . ± . − . ± .
031 15.123 0 .
617 yes HB 177 15 18 31.070 +02 02 42.76 − . ± . . ± . − . ± .
129 14.574 0 .
879 yes HB 186093/ 1 16 17 04.351 −
22 59 11.72 0 . ± . − . ± . − . ± .
029 13.660 1 .
573 no? 19M80 2 16 17 15.936 −
22 58 28.32 1 . ± . − . ± . − . ± .
021 13.826 0 .
982 no3 16 17 01.555 −
22 58 30.68 . . . . . . . . . .
313 yes? CV? 204 16 17 11.479 −
23 01 57.38 1 . ± . − . ± . − . ± .
100 13.842 1 .
131 no5 16 17 08.152 −
22 56 32.05 2 . ± . − . ± . − . ± .
020 12.124 0 .
898 no6121/ 1 16 23 32.449 −
26 26 45.86 5 . ± . . ± . − . ± .
019 11.182 1 .
128 noM4 2 16 23 35.031 −
26 25 36.49 0 . ± . − . ± . − . ± .
018 13.183 1 .
087 yes HB 213 16 23 39.404 −
26 34 54.53 4 . ± . . ± . − . ± .
018 10.103 1 .
189 no4 16 23 29.185 −
26 28 54.38 0 . ± . − . ± . − . ± .
018 13.161 1 .
095 yes HB 225 16 23 36.469 −
26 30 44.33 0 . ± . − . ± . − . ± .
022 12.894 0 .
992 yes HB 236 16 23 47.824 −
26 32 05.99 0 . ± . − . ± . − . ± .
016 13.395 0 .
605 yes HB 247 16 23 48.797 −
26 35 09.17 0 . ± . − . ± . − . ± .
036 11.026 1 .
888 yes RGB 25
Table 1 continued
Bond
Table 1 (continued)
Cluster ZNG RA Dec Parallax µα µδ G BP − RP Cluster Classi- RemarkscNGC/M No. [J2000] [J2000] [mas] [mas yr −
1] [mas yr −
1] [mag] [mag] Member?a ficationb8 16 23 50.103 −
26 36 09.55 0 . ± . − . ± . − . ± .
017 12.894 0 .
731 yes HB9 16 23 53.591 −
26 30 05.35 0 . ± . − . ± . − . ± .
021 12.946 1 .
016 yes HB 266205/ 1 16 41 33.666 +36 26 07.78 0 . ± . − . ± . − . ± .
033 13.123 − .
255 yes vPAGB 27M13 2 16 41 34.759 +36 29 13.89 2 . ± . − . ± . − . ± .
464 14.270 0 .
267 yes? AHB 283 16 41 52.090 +36 26 28.90 0 . ± . − . ± . − . ± .
018 14.089 0 .
182 yes AHB 294 16 41 36.437 +36 30 51.67 0 . ± . − . ± . − . ± .
021 14.055 0 .
206 yes AHB 305 16 41 19.580 +36 21 15.62 0 . ± . − . ± . − . ± .
019 11.380 1 .
442 no6 16 41 43.018 +36 28 42.20 0 . ± . − . ± . − . ± .
027 14.646 0 .
014 yes AHB7 16 41 08.024 +36 30 05.38 0 . ± . − . ± . − . ± .
034 15.361 − .
185 yes AHB6218/ 1 16 47 18.547 −
02 00 10.86 1 . ± . − . ± . − . ± .
012 12.326 1 .
005 noM12 2 16 47 00.790 −
01 58 28.25 0 . ± . − . ± . − . ± .
013 12.587 1 .
294 no3 16 47 12.136 −
01 54 06.92 1 . ± . − . ± .
015 8 . ± .
012 11.926 1 .
300 no4 16 47 08.603 −
02 01 37.07 0 . ± . − . ± . − . ± .
011 12.479 1 .
338 no5 16 47 45.287 −
01 55 03.50 0 . ± . − . ± . − . ± .
012 13.183 0 .
915 no6 16 47 27.241 −
01 52 19.49 1 . ± . . ± . − . ± .
015 13.590 0 .
921 no7 16 47 18.056 −
01 58 17.40 0 . ± . − . ± . − . ± .
013 12.690 1 .
401 yes AGB 318 16 47 25.974 −
02 01 03.39 0 . ± . − . ± . − . ± .
010 12.136 1 .
435 yes AGB 329 16 47 39.628 −
02 01 25.49 1 . ± . . ± . − . ± .
016 13.089 0 .
876 no6254/ 1 16 57 09.253 −
04 04 24.40 0 . ± . − . ± . − . ± .
019 13.485 0 .
016 yes bPAGB 33M10 2 16 57 09.836 −
04 04 28.50 0 . ± . − . ± . − . ± .
017 13.729 0 .
354 yes AHB3 16 57 18.697 −
04 09 06.82 0 . ± . . ± . − . ± .
020 11.152 1 .
434 no4 16 57 10.387 −
04 04 01.74 0 . ± . − . ± . − . ± .
014 13.026 1 .
525 yes RGB5 16 57 05.571 −
04 06 52.31 0 . ± . − . ± . − . ± .
029 13.998 0 .
426 yes AHB6 16 57 06.332 −
04 07 17.03 0 . ± . − . ± . − . ± .
069 13.940 0 .
741 yes AHB7 16 57 12.231 −
04 11 26.97 1 . ± . − . ± .
024 2 . ± .
019 11.398 1 .
392 no8 16 56 57.629 −
04 07 16.03 0 . ± . − . ± . − . ± .
018 14.248 0 .
376 yes AHB6273/ 1 17 02 41.532 −
26 15 16.42 0 . ± . − . ± . − . ± .
012 12.083 0 .
526 noM19 2 17 02 39.154 −
26 15 29.36 0 . ± . − . ± .
025 1 . ± .
018 13.207 0 .
518 yes bPAGB 343 17 02 38.139 −
26 15 11.75 0 . ± . − . ± .
048 1 . ± .
033 13.342 1 .
404 yes? AHB 354 17 02 35.185 −
26 15 24.13 0 . ± . − . ± .
019 1 . ± .
012 12.204 1 .
238 yes yPAGB 365 17 02 24.171 −
26 14 40.71 1 . ± . − . ± . − . ± .
013 12.718 0 .
931 no6 17 02 26.447 −
26 16 08.28 1 . ± . − . ± . − . ± .
353 13.570 1 .
285 no6333/ 1 17 19 15.461 −
18 31 10.71 0 . ± . − . ± . − . ± .
014 12.836 0 .
561 yes? bPAGB 37M9 2 17 19 05.776 −
18 32 53.32 0 . ± . . ± . − . ± .
012 13.187 0 .
569 no3 17 19 03.581 −
18 30 43.67 2 . ± . . ± . − . ± .
012 13.308 1 .
147 no4 17 19 05.924 −
18 31 33.16 0 . ± . − . ± . − . ± .
137 14.480 0 .
787 yes? AHB 386341/ 1 17 16 56.770 +43 05 36.82 2 . ± . . ± . − . ± .
015 11.670 0 .
576 noM92 2 17 17 03.850 +43 05 50.45 4 . ± . − . ± . − . ± .
047 12.679 1 .
085 no3 17 16 58.376 +43 01 18.04 1 . ± . − . ± .
016 0 . ± .
016 12.953 0 .
775 no4 17 16 29.018 +43 09 43.80 0 . ± . − . ± . − . ± .
012 13.328 0 .
943 no 396356 1 17 23 32.455 −
17 49 38.41 1 . ± . . ± . − . ± .
020 14.380 1 .
101 no2 17 23 29.547 −
17 49 10.62 0 . ± . . ± . − . ± .
021 14.265 1 .
482 yes? AHB 403 17 23 40.827 −
17 49 24.47 0 . ± . − . ± .
099 1 . ± .
074 14.820 1 .
295 no6402/ 1 17 37 33.178 −
03 14 51.68 0 . ± . − . ± . − . ± .
026 14.538 0 .
863 yes bPAGB 41M14 2 17 37 33.434 −
03 16 09.89 1 . ± . − . ± .
019 5 . ± .
014 13.217 1 .
356 no3 17 37 44.596 −
03 11 50.37 0 . ± . . ± . − . ± .
017 13.696 1 .
000 no4 17 37 48.410 −
03 15 47.78 2 . ± . . ± . − . ± .
050 13.446 1 .
482 no5 17 37 30.986 −
03 15 03.77 0 . ± . − . ± . − . ± .
033 15.257 0 .
842 yes AHB 426 17 37 33.749 −
03 15 42.09 − . ± . − . ± . − . ± .
039 14.642 1 .
128 yes AHB7 17 37 31.877 −
03 14 52.47 − . ± . − . ± . − . ± .
029 15.353 0 .
966 yes AHB8 17 37 21.521 −
03 15 18.01 1 . ± . . ± .
094 0 . ± .
074 14.727 1 .
345 no9 17 37 27.238 −
03 12 56.63 1 . ± . . ± .
024 10 . ± .
019 14.759 1 .
510 no10 17 37 35.767 −
03 16 29.98 0 . ± . − . ± . − . ± .
028 15.569 0 .
916 yes AHB11 17 37 48.235 −
03 15 52.97 2 . ± . . ± . − . ± .
014 13.862 1 .
458 no12 17 37 42.232 −
03 14 59.35 0 . ± . − . ± . − . ± .
071 15.622 0 .
895 yes AHB13 17 37 26.563 −
03 17 15.06 0 . ± . − . ± . − . ± .
010 12.538 1 .
842 no14 17 37 33.474 −
03 15 27.77 − . ± . − . ± . − . ± .
026 14.980 1 .
689 yes AHB 436626/ 1 18 24 34.602 −
24 53 21.19 0 . ± . . ± . − . ± .
024 12.928 0 .
765 noM28 2 18 24 28.326 −
24 54 24.28 0 . ± . . ± . − . ± .
028 12.760 0 .
599 no3 18 24 29.356 −
24 50 47.10 0 . ± . . ± .
042 0 . ± .
030 13.733 0 .
815 no
Table 1 continued he ZNG Catalog of UV-Bright Stars Table 1 (continued)
Cluster ZNG RA Dec Parallax µα µδ G BP − RP Cluster Classi- RemarkscNGC/M No. [J2000] [J2000] [mas] [mas yr −
1] [mas yr −
1] [mag] [mag] Member?a ficationb4 18 24 31.597 −
24 49 16.99 1 . ± . . ± . − . ± .
017 12.554 0 .
762 no5 18 24 35.838 −
24 53 15.87 0 . ± . . ± . − . ± .
021 11.610 1 .
755 yes rPAGB 446656/ 1 18 36 13.295 −
23 52 46.13 4 . ± . . ± .
018 11 . ± .
013 10.969 1 .
043 noM22 2 18 36 40.101 −
23 52 51.13 3 . ± . . ± . − . ± .
013 11.812 1 .
011 no3 18 36 49.468 −
23 55 48.96 1 . ± . − . ± . − . ± .
013 11.863 0 .
983 no4 18 36 35.319 −
23 48 20.50 1 . ± . . ± . − . ± .
028 11.576 0 .
697 no5 18 36 10.796 −
23 49 57.14 0 . ± . . ± . − . ± .
014 12.519 0 .
668 yes AHB6 18 36 30.544 −
23 53 58.10 0 . ± . . ± . − . ± .
017 10.970 1 .
805 yes AGB7 18 36 24.181 −
23 52 57.09 0 . ± . . ± . − . ± .
014 10.782 1 .
975 yes RGB8 18 35 50.312 −
23 58 25.91 1 . ± . . ± . − . ± .
038 10.999 0 .
578 no9 18 36 49.548 −
24 01 16.01 0 . ± . − . ± . − . ± .
116 11.898 0 .
950 no10 18 35 52.789 −
23 53 34.20 1 . ± . . ± . − . ± .
016 10.210 1 .
730 no11 18 36 33.013 −
23 54 35.71 1 . ± . . ± . − . ± .
015 10.999 1 .
438 no12 18 36 15.426 −
23 46 17.40 1 . ± . . ± .
021 1 . ± .
017 12.369 0 .
501 no13 18 36 10.475 −
23 46 27.45 1 . ± . . ± . − . ± .
080 10.501 0 .
537 no14 18 35 54.081 −
23 45 31.73 0 . ± . . ± . − . ± .
016 10.931 1 .
750 yes AGB 4515 18 35 43.009 −
23 48 32.99 5 . ± . − . ± . − . ± .
016 10.792 0 .
985 no16 18 36 29.196 −
23 49 53.24 0 . ± . . ± . − . ± .
016 13.520 0 .
356 no17 18 36 53.525 −
23 51 29.50 1 . ± . . ± .
017 0 . ± .
013 9.739 1 .
431 no18 18 36 28.974 −
24 04 04.05 1 . ± . . ± . − . ± .
016 12.822 0 .
949 no6712 1 18 53 05.791 −
08 42 37.85 0 . ± . . ± . − . ± .
014 13.135 0 .
556 yes bPAGB 462 18 53 07.295 −
08 43 09.29 0 . ± . . ± .
027 0 . ± .
021 13.870 0 .
797 no3 18 53 01.434 −
08 42 33.89 1 . ± . . ± . − . ± .
022 14.109 0 .
986 no4 18 53 08.772 −
08 41 56.66 0 . ± . . ± . − . ± .
017 12.025 2 .
443 yes AGB 476779/ 1 19 16 36.583 +30 11 17.37 0 . ± . − . ± . − . ± .
183 14.423 0 .
969 noM56 2 19 16 41.278 +30 12 48.55 0 . ± . − . ± .
021 1 . ± .
025 15.099 − .
038 yes vPAGB 486934 1 20 34 07.304 +07 23 47.01 0 . ± . . ± . − . ± .
017 14.528 0 .
874 no7078/ 1 21 29 58.194 +12 11 42.55 0 . ± . − . ± . − . ± .
039 15.065 0 .
053 yes AHB 49M15 2 21 30 07.438 +12 11 07.73 0 . ± . − . ± . − . ± .
017 14.313 0 .
137 yes AHB3 21 29 44.092 +12 09 16.73 1 . ± . − . ± . − . ± .
012 13.477 0 .
910 no4 21 30 00.789 +12 09 43.28 − . ± . − . ± . − . ± .
192 13.820 1 .
160 yes AGB 505 21 29 55.072 +12 10 14.49 − . ± . − . ± . − . ± .
033 13.119 1 .
373 yes AGB 516 21 29 56.179 +12 10 17.93 0 . ± . − . ± . − . ± .
045 12.352 1 .
511 no? 527 21 30 00.981 +12 08 41.83 − . ± . − . ± . − . ± .
091 15.194 0 .
230 yes? AHB 537089/ 1 21 33 34.128 −
00 53 37.99 0 . ± . . ± . − . ± .
021 14.570 0 .
139 yes AHBM2 2 21 33 29.872 −
00 45 51.60 − . ± . . ± . − . ± .
065 15.113 0 .
162 yes AHB a Indication of cluster membership, based on parallax and proper motion. A few uncertain cases are labeled with question marks. b Evolutionary classification scheme is explained in text ( §
6) and Figure 2 caption; based on position in
Gaia color-magnitude diagrams. Abbreviations are: AGB (asymptotic-giant branch); RGB (red-giant branch); HB (horizontal branch); rPAGB, yPAGB, bPAGB, and vPAGB (red, yellow, blue, and violet post-AGB stars); AHB (abovehorizontal branch); and CV (cataclysmic variable). c Remarks: [1] 4147 ZNG 2:
HST images show object to be blend of 5 cluster members of similar brightness; brightest one listed. [2] 4590 ZNG 2: At tip of AGB/RGB; seeSchaeuble et al. (2015) and references therein. [3] 5024 ZNG 3: considered a non-member by Boberg et al. (2016). [4] 5024 ZNG 7: Close nearly equal pair, separation0”.9. Astrometry has large uncertainties, but both components consistent with membership. Brighter component listed. Non-member according to Boberg et al. (2016).[5] 5024 ZNG 8: Astrometry has large uncertainties. Member according to Boberg et al. (2016). [6] 5024 ZNG 9: Member according to Boberg et al. (2016). Blended witha fainter AGB star 2 . ′′ Gaia
RVconsistent with membership. [15] 5904 ZNG 1: Proper motion consistent with membership, parallax discordant; AGB or RGB star if member. [16] 5904 ZNG 2: Propermotion consistent with membership, parallax discordant; AGB or RGB tip star if member. [17] 5904 ZNG 6: RR Lyr variable V41. [18] 5904 ZNG 7: RR Lyr variableV25. [19] 6093 ZNG 1: Proper motion consistent with membership, parallax discordant; RGB star if member. [20] 6093 ZNG 3: EDR3 does not give a parallax or propermotion for this source; there is a bright blue object at this position in
HST images, but the
Gaia BP − RP color is red. Position is close to that of the X-ray source CX3(Heinke et al. 2003). [21] 6121 ZNG 2: RR Lyr variable V19. [22] 6121 ZNG 4: RR Lyr variable V10. [23] 6121 ZNG 5: This object is a blend of two RR Lyr variables,separated by 1 . ′′ Gaia
RV consistent with membership. [26] 6121 ZNG 9: RR Lyr variable V28. [27] 6205 ZNG 1: Barnard 29(see M+19). [28] 6205 ZNG 2: Proper motion consistent with membership, but large uncertainties and discordant parallax; suspected low-amplitude variable (Deras et al.2019). [29] 6205 ZNG 3: Variable star V51, uncertain type (Servillat et al. 2011). [30] 6205 ZNG 4: Spectroscopic analysis by Ambika et al. (2004). [31] 6218 ZNG 7:
Gaia
RV consistent with membership. [32] 6218 ZNG 8:
Gaia
RV consistent with membership. [33] 6254 ZNG 1: Blue PAGB star (see M+19). [34] 6273 ZNG 2: BluePAGB star (see B+21). [35] 6273 ZNG 3: Type II Cepheid, V1 (Clement & Sawyer Hogg 1978); proper motion consistent with membership, parallax discordant. [36]6273 ZNG 4: Yellow PAGB star (see B+21). [37] 6333 ZNG 1: Proper motion consistent with membership; parallax slightly discrepant. On boundary between yellow andblue PAGB stars. [38] 6333 ZNG 4: Astrometry consistent with membership, but uncertainties are large. [39] 6341 ZNG 4: Proper motion consistent with membership,but parallax is discordant. Considered a member by Zinn (1974), but not by Roederer & Sneden (2011). [40] 6356 ZNG 2: Proper motion marginally consistent withmembership. [41] 6402 ZNG 1: Blue PAGB star (star 33 in Schiavon et al. 2012). [42] 6402 ZNG 5: Above HB (star 202 in Schiavon et al. 2012). [43] 6402 ZNG 14: TypeII Cepheid, V167 (Contreras Pe˜na et al. 2018). [44] 6626 ZNG 5: RV Tauri variable V2342 Sgr = V17. [45] 6656 ZNG 14:
Gaia
RV consistent with membership. [46]6712 ZNG 1: Blue PAGB star (see M+19). [47] 6712 ZNG 4: Luminous star at AGB tip; Mira variable AP Sct = V2. [48] 6779 ZNG 2: Violet PAGB star (see M+19).[49] 7078 ZNG 1: Hot post-HB or violet PAGB star (see M+19). [50] 7078 ZNG 4: Identification difficult and uncertain. Listed star is brighter of close 1 . ′′ . ′′′′