PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 112 :251È263, 2000 February2000. The Astronomical Society of the PaciÐc. All rights reserved. Printed in U.S.A.(

A Finding List of Faint UV-bright Stars in the Galactic Plane. V.HOWARD H. LANNING

Computer Sciences Corporation/Science Programs, Space Telescope Science Institute, Baltimore, MD 21218 ; lanning=stsci.edu

AND

MICHAEL MEAKES

Space Telescope Science Institute, Baltimore, MD 21218 ; meakes=stsci.edu

Received 1999 July 9 ; accepted 1999 November 4

ABSTRACT. Four additional plates from the Sandage Two-Color Survey of the Galactic Plane have beenexamined, yielding identiÐcations of 108 UV-bright stars. The plates examined were obtained using thePalomar 48 inch Oschin Schmidt telescope and cover a Ðeld of view of The plates were centered at6¡.6 ] 6¡.6.the Galactic longitude (l) and latitude (b) coordinates of ]0¡), [6¡), (100¡, ]4¡), and(80¡.4, (80¡.4, (104¡.1,]6¡). IdentiÐed sources range in U[B color from U[BD [0.1 to U[BD [1.0 and in magnitude from

to D20. Accurate J2000 coordinates and Ðnding charts are provided for all the UV candidatesmBD 10

included, and some of the more interesting sources are discussed. Previously identiÐed objects referenced inthe literature are noted.

1. INTRODUCTION

This paper is the Ðfth in a series of catalogs providingidentiÐcations of faint UV-bright sources found in the con-tinuing program to examine plates from the Sandage Two-Color Survey of the Galactic Plane.1 The program was Ðrstdescribed by Lanning (1973, hereafter Paper I). TheSandage two-color photographic survey was originallybegun in support of the Uhuru X-ray satellite with the goalof identifying and studying the optical counterparts ofnewly detected X-ray sources expected to lie along theGalactic plane. More than 100 plates measuring on a6¡.6side were obtained with the Palomar 48 inch OschinSchmidt telescope. Plates were centered at Galactic lati-tudes of ]6¡ , 0¡, and [6¡, thus covering a range of Galac-tic latitude of ^9¡ and extending throughout most of thenorthern plane (l\ 0¡È227¡). Adjacent plate Ðelds wereslightly overlapped to avoid gaps in the survey. Each platewas double-exposed, one image in the UV (UG1 Ðlter), thesecond image in the blue (GG13). The telescope was o†setbetween exposures providing a separation between imagesof 12A. The U[B color di†erence calibration was designedto produce a U[B\ 0 for equal-sized images. O†sets inthe color di†erence calibration of up to 0.5 mag were notedfor some plates presented here. In all such cases the balanceo†set observed indicated an equal-sized pair was slightly

ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ1 Information related to this survey including published papers, Ðnding

charts, updated tables, etc., may be viewed on the WWW site devoted tothe survey, http ://www.stsci.edu/Dlanning/index.html.

bluer than U[B\ 0. The larger image in the U Ðlter typi-cally suggests the presence of bluer objects such as low-luminosity stars, white dwarfs, novae, cataclysmic variables,normal early B stars, and blue subdwarfs. This multicolorphotographic technique has been described by Haro &Herbig (1955).

The data presented in this paper represent a careful visualexamination of four plates from the survey centered atGalactic coordinate (l, b) regions ]0¡), [6¡),(80¡.4, (80¡.4,(100¡, ]4¡), and ]6¡). It should not be assumed,(104¡.1,however, that every potential UV source present on theplates was identiÐed. We noted previously (Lanning &Meakes 1997) that several plates had been scanned usingthe KPNO PDS microdensitometer at 10 km sampling.However, due to extreme crowding of images in the Galac-tic plane, many visually obvious UV-bright sources couldnot be reliably detected. Difficulties encountered in setting athreshold for the aperture used limited the range and accu-racy of source identiÐcations, even though the visual exami-nations of sources in crowded Ðelds could clearly revealtheir bluer nature, a feature attributed to the increaseddynamic range of the eye. It was therefore concluded thatcontinuation of the visual scanning of plates in the Sandagesurvey was strongly justiÐed.

All sources described in this paper are the result of acomprehensive survey of the entire 43 deg2 Ðeld on each ofthe Schmidt plates examined. Although the original intentof the Sandage two-color survey was to support the opticalidentiÐcation of X-ray sources, as noted above, the UV-bright sources found during this analysis do not necessarily

251

252 LANNING & MEAKES

TABLE 1

FINDING LIST OF UV SOURCES

Lanning Sandage R.A. Decl. Corresponding IDs, Spectral Type, U[BNumber Plate ID (2000) (2000) m

BU[B Magnitude, Notes

(1) (2) (3) (4) (5) (6) (7)

356 . . . . . . 80.4]0 20 24 33.0 ]41 23 37.2 17.0 [0.4354 . . . . . . 20 25 09.0 ]42 47 25.0 15.5 [0.2362 . . . . . . 20 29 18.9 ]40 15 19.2 . . . . . . PN G078.9]00.7355 . . . . . . 20 29 54.9 ]42 43 15.2 19.0 [0.5357 . . . . . . 20 32 38.4 ]41 13 41.5 20.0 [0.4358 . . . . . . 20 33 52.7 ]40 56 47.3 18.3 [0.3360 . . . . . . 20 38 22.6 ]40 17 34.4 18.5 [0.2352 . . . . . . 20 39 03.0 ]43 30 40.9 11.5 [0.3361 . . . . . . 20 48 08.3 ]39 51 38.3 14.0 [0.9 KPD 2046]3940 ; DAw359 . . . . . . 20 50 29.7 ]40 20 33.5 12.0 [0.3366 . . . . . . 80.4[6 20 54 27.0 ]42 42 47.7 18.0 [0.4353 . . . . . . 80.4]0 20 54 27.3 ]42 42 44.4 18.0 [0.3377 . . . . . . 80.4[6 20 54 36.3 ]40 33 18.8 10.8 [0.3376 . . . . . . 20 55 47.3 ]40 47 59.4 11.2 [0.4372 . . . . . . 20 55 47.9 ]41 37 35.4 11.8 [0.3378 . . . . . . 20 56 34.2 ]40 19 09.9 10.7 [0.3364 . . . . . . 20 56 37.2 ]43 13 26.3 17.0 [0.2391 . . . . . . 20 57 09.1 ]38 11 57.9 16.2 [0.5367 . . . . . . 21 04 02.6 ]42 47 03.5 15.5 [0.3382 . . . . . . 21 06 36.4 ]39 13 22.2 16.0 [0.5393 . . . . . . 21 07 47.7 ]38 02 56.0 11.3 [0.3386 . . . . . . 21 08 34.0 ]39 05 36.5 15.8 [0.5390 . . . . . . 21 11 17.7 ]38 43 34.7 11.0 [0.3 In Ðeld of Cyg X-4392 . . . . . . 21 13 40.5 ]38 13 02.8 17.5 [0.6363 . . . . . . 21 15 51.1 ]43 29 02.9 18.5 [0.2389 . . . . . . 21 16 04.8 ]38 46 44.0 17.5 [0.5426 . . . . . . 100]4 21 16 25.8 ]58 34 03.5 11.8 [0.3 Cep OB2 association, Trumpler 37 904 ; B8401 . . . . . . 21 16 59.3 ]60 40 30.3 11.6 [0.1425 . . . . . . 21 17 48.3 ]58 43 33.5 10.9 [0.2 Cep OB2 association, Trumpler 37 1196 ; F8456 . . . . . . 21 18 17.4 ]55 03 43.1 18.5 [0.2 In region of X-ray source H2116]55383 . . . . . . 80.4[6 21 18 32.4 ]39 19 26.0 17.0 [0.6407 . . . . . . 100]4 21 19 48.2 ]60 21 01.3 18.8 [0.8438 . . . . . . 21 19 48.9 ]57 29 39.5 11.0 [0.4 Cep OB2 association, Trumpler 37 339 ; B8388 . . . . . . 80.4[6 21 19 53.1 ]38 44 24.1 16.5 [0.4385 . . . . . . 21 20 11.7 ]39 01 03.7 16.0 [0.5430 . . . . . . 100]4 21 20 42.1 ]58 19 25.4 17.0 [0.5 WD 2119]58, GD 548 ; DA white dwarf457 . . . . . . 21 21 51.9 ]55 05 16.2 19.0 [0.5427 . . . . . . 21 21 55.9 ]58 37 47.3 11.1 [0.1 Cep OB2 association, Trumpler 37 940 ; G2384 . . . . . . 80.4[6 21 23 09.3 ]38 58 11.3 16.5 [0.2387 . . . . . . 21 23 10.4 ]38 43 19.4 19.0 [0.4369 . . . . . . 21 23 12.8 ]42 01 52.4 10.6 [0.3371 . . . . . . 21 23 28.8 ]41 46 33.3 10.5 [0.3379 . . . . . . 21 23 31.8 ]40 16 05.9 10.8 [0.2381 . . . . . . 21 23 42.4 ]39 24 58.4 10.6 [0.2370 . . . . . . 21 24 19.1 ]41 58 41.3 10.7 [0.4365 . . . . . . 21 24 22.1 ]42 50 18.0 10.2 [0.2406 . . . . . . 100]4 21 24 44.9 ]60 35 17.5 12.4 [0.1380 . . . . . . 80.4[6 21 24 46.9 ]39 42 29.9 10.6 [0.2368 . . . . . . 21 24 53.4 ]42 40 02.0 10.5 [0.2375 . . . . . . 21 25 08.0 ]40 53 16.9 10.5 [0.2394 . . . . . . 100]4 21 25 08.3 ]61 24 34.4 19.8 [0.6373 . . . . . . 80.4[6 21 25 18.6 ]41 28 26.8 10.8 [0.2374 . . . . . . 21 26 24.0 ]41 14 20.0 10.8 [0.3400 . . . . . . 100]4 21 26 38.1 ]60 58 27.1 19.2 [0.6

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FINDING LIST OF UV-BRIGHT STARS. V. 253

TABLE 1ÈContinued

Lanning Sandage R.A. Decl. Corresponding IDs, Spectral Type, U[BNumber Plate ID (2000) (2000) m

BU[B Magnitude, Notes

(1) (2) (3) (4) (5) (6) (7)

451 . . . . . . 21 26 40.6 ]55 36 53.3 17.0 [0.5431 . . . . . . 21 26 58.8 ]58 19 44.8 19.8 [0.8424 . . . . . . 21 28 10.8 ]58 52 35.6 19.2 [0.6416 . . . . . . 21 28 10.9 ]59 27 13.4 19.0 [1.0439 . . . . . . 21 28 22.9 ]57 38 04.7 19.6 [0.6402 . . . . . . 21 29 15.4 ]60 52 45.9 19.0 [0.5441 . . . . . . 21 29 41.9 ]56 43 07.7 14.5 [0.7410 . . . . . . 21 29 58.7 ]60 07 21.7 11.0 [0.1 Cep OB2 association, Trumpler 37 1756 ; A0443 . . . . . . 21 30 14.4 ]56 26 13.3 10.8 [0.2409 . . . . . . 21 30 36.9 ]60 19 53.0 10.7 [0.1 Cep OB2 association, Trumpler 37 1976 ; B8395 . . . . . . 21 32 59.6 ]61 09 18.6 18.9 [1.0403 . . . . . . 21 33 14.4 ]60 48 30.4 17.3 [0.6435 . . . . . . 21 33 29.0 ]58 11 17.2 17.5 [0.7411 . . . . . . 21 33 58.1 ]60 02 20.0 16.8 [0.8444 . . . . . . 21 35 20.5 ]56 10 49.5 17.0 [0.9434 . . . . . . 21 35 42.1 ]58 07 31.4 14.0 [0.1 Cep OB2 association, Trumpler 37 Kun 310396 . . . . . . 21 36 07.9 ]61 10 33.7 19.5 [0.4455 . . . . . . 21 36 17.3 ]55 20 26.6 12.0 [0.3 LS III ]55¡12 ; B404 . . . . . . 21 36 43.7 ]60 43 56.3 10.8 [0.2429 . . . . . . 21 36 55.0 ]58 30 04.7 19.0 [0.9445 . . . . . . 21 37 40.3 ]56 10 14.0 18.8 [0.8449 . . . . . . 21 38 35.6 ]55 50 53.3 11.2 [0.1417 . . . . . . 21 38 53.1 ]59 29 08.6 18.5 [0.6448 . . . . . . 21 39 22.4 ]55 59 32.7 11.5 [0.2453 . . . . . . 21 39 51.7 ]55 28 03.2 11.3 [0.4 BD]54¡2592 ; LS III ]55¡13 ; B452 . . . . . . 21 39 51.9 ]55 33 01.0 11.5 [0.2414 . . . . . . 21 40 10.9 ]59 55 38.3 11.2 [0.1 Cep OB2 association, Trumpler 37 1790 ; F8442 . . . . . . 21 41 21.0 ]56 35 18.3 19.8 [0.4454 . . . . . . 21 41 41.1 ]55 27 50.2 11.4 [0.5399 . . . . . . 21 41 41.3 ]60 58 54.6 13.8 [0.7423 . . . . . . 21 42 14.7 ]58 54 01.7 16.5 [0.4422 . . . . . . 21 43 56.4 ]58 56 35.9 18.8 [0.8440 . . . . . . 21 49 11.1 ]57 27 24.5 19.5 [0.6418 . . . . . . 21 50 36.0 ]59 27 07.6 19.8 [0.7408 . . . . . . 21 51 06.2 ]60 16 23.0 12.2 [0.3446 . . . . . . 21 51 09.6 ]56 10 40.2 12.0 [0.3433 . . . . . . 21 51 32.4 ]58 09 11.6 18.5 [1.0447 . . . . . . 21 57 49.2 ]56 12 27.6 11.0 [0.5 LS III ]55¡19 ; B ([0.40)432 . . . . . . 21 58 32.5 ]58 04 33.4 18.5 [0.6419 . . . . . . 21 58 39.5 ]59 21 57.8 10.5 [0.2437 . . . . . . 21 59 19.7 ]57 39 23.2 15.5 [0.6397 . . . . . . 21 59 49.6 ]61 06 52.5 11.2 [0.5405 . . . . . . 22 00 01.4 ]60 44 56.0 10.8 [0.3415 . . . . . . 22 00 25.2 ]59 41 30.6 11.2 [0.5 DL Cep; b Lyrae type eclipsing binary450 . . . . . . 22 01 22.5 ]55 34 52.4 11.0 [0.2436 . . . . . . 22 02 10.5 ]57 38 03.0 10.8 [0.6421 . . . . . . 22 02 43.0 ]58 44 55.1 10.8 [0.2420 . . . . . . 22 02 43.1 ]59 03 20.2 17.2 [0.7 Nova?428 . . . . . . 22 03 20.4 ]58 23 37.2 10.9 [0.1412 . . . . . . 22 03 43.7 ]59 58 45.9 10.9 [0.6 LS III ]59¡19 ; B398 . . . . . . 22 03 47.1 ]60 56 37.6 10.8 [0.1413 . . . . . . 22 04 38.4 ]59 59 43.0 17.8 [0.7459 . . . . . . 104.1]6 22 05 38.2 ]62 24 35.7 16.0 [0.8458 . . . . . . 22 45 16.4 ]66 08 13.3 18.0 [0.5

NOTE.ÈUnits of right ascension are hours, minutes, and seconds, and units of declination are degrees, arcminutes, andarcseconds.

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254 LANNING & MEAKES

FIG. 1.ÈLanning 362 is the planetary nebula PN G078.9]00.7. The nebula appears very faint in both the B and U colors on the survey plate with a slightUV excess. The scale of all charts is D11 arcsec mm~1. North is up and east to the left.

254

FINDING LIST OF UV-BRIGHT STARS. V. 255

FIG. 2.ÈNorth is up and east to the left

255

256 LANNING & MEAKES

FIG. 3.ÈThe magnitude and color estimate for Lanning 364 may be slightly uncertain due to the inÑuence of what appears to be faint nebulosity ormerged nearby objects. Lanning 394 is the northern component of the pair. North is up and east to the left.

256

FINDING LIST OF UV-BRIGHT STARS. V. 257

FIG. 4.ÈOn the chart for Lanning 407, the UV source is the faint southern component of the pair. Additionally, the source Lanning 411 is the northerncomponent of the pair on its chart. North is up and east to the left.

257

258 LANNING & MEAKES

FIG. 5.ÈLanning 420 is not visible on the Digitized Sky Survey image, but is very blue on the survey plate. The source is clearly variable and could be afaint nova. North is up and east to the left.

258

FINDING LIST OF UV-BRIGHT STARS. V. 259

FIG. 6.ÈLanning 433 is the southeast component of the pair. Background contamination from the bright star adjacent to Lanning 437 may contribute tothe uncertainty in estimating an accurate magnitude and color for the UV source. North is up and east to the left.

259

260 LANNING & MEAKES

FIG. 7.ÈNorth is up and east to the left

correspond to previously discovered X-ray sources. Paper Icontained a list of 82 UV sources identiÐed from the exami-nation of 17 plates in the survey. An additional 53 sourceswere presented in Lanning & Meakes (1994, hereafter PaperII) from the examination of three plates, 62 sources wereidentiÐed on the next three plates examined for Lanning &Meakes (1995, hereafter Paper III), and 156 sources weretabulated in Lanning & Meakes (1998, hereafter Paper IV).The total number of sources reported in Papers IIÈIV varysigniÐcantly from those in Paper I. As noted in Paper III, a

review of the regions examined showed a clear trend towardhigher rates of detection of UV-bright sources at the edgesof the Galactic plane, i.e., for the ]6¡ or [6¡ survey platecenters. Many of those sources will most likely be identiÐedas normal hot, early-type stars which do not su†er from thegreater reddening e†ects evident in the central regions of theplane. All plates examined in Papers II and III, one plate inPaper IV, and two of the four plates in this work werecentered at the ]6¡ or [6¡ centers. As evidence of thereduced reddening in these regions, the SIMBAD output for

2000 PASP, 112 :251È263

FINDING LIST OF UV-BRIGHT STARS. V. 261

many of the sources corresponding to the [6¡ plate inPaper IV listed a number of galaxies in the vicinity of theUV-bright source positions queried.

2. THE FINDING LIST

Table 1 contains the list of 108 ultraviolet objects foundon the plates examined in this portion of the surveyanalysis. Each plate was scanned in a raster pattern on aplate rack using a stereoscopic microscope. The Ðelds wereoverlapped slightly to prevent omission of potential sourcesat the edges of the microscope Ðeld of view. The blue magni-tude and color (U[B) for each source has been estimatedby visual inspection of the plates. Where possible, photo-electric measurements determined by Hoag et al. (1961) forGalactic cluster Ðelds were used to calibrate the magnitudesand colors of sources on the plates. Alternatively, for platescontaining no Galactic clusters, photometry provided byBlanco et al. (1970) and Giclas, Burnham, & Thomas (1971)was used. Magnitude and color estimates have previouslybeen quoted as good only to ^0.5 mag due to such contrib-uting factors as variation in plate balance, image distortionresulting from guiding errors or other mechanical factors,e.g., plate holder nonuniformities and general uncertaintiesrelated to obtaining accurate visual estimates from pho-tographic plates. To verify this assertion, magnitude andcolor estimates for sources in previous papers were com-pared to published B and U[B values. An accuracy of^0.5 mag remains valid for the B magnitude, althoughselected di†erences may range as high as 1.1 mag, particu-larly for brighter sources and distorted images. The com-puted accuracy for the U[B colors was found to be muchbetter, typically in the range of ^0.15 mag. Again, selecteddi†erences due to various plate e†ects may be as high as0.45 mag, however. Presentation of UV-bright sources iden-tiÐed during this analysis was restricted to objects with

or fainter due to uncertainties associated with themBD 10

merging of images for the brighter sources.The format of Table 1 consists of (1) the Lanning source

number, (2) the Sandage plate identiÐcation (plate center inGalactic coordinates), (3) right ascension (equinox J2000),(4) declination (equinox J2000), (5) estimated photographicblue magnitude, (6) estimated U[B color di†erence, and (7)corresponding identiÐcations with previously knownsources along with general notes, e.g., the spectral type andU[B color stored in SIMBAD. Source numbers follow theconvention established by the SIMBAD (Sets of IdentiÐca-tions, Measurements, and Bibliography for AstronomicalData) database entries for Paper I. Sources are sorted inorder of right ascension for the four plates presented in thiswork.

The GS Astrometric Support Program (GASP) was usedto determine accurate positions of the sources listed in

Table 1. These positions were measured from imagesretrieved from the Space Telescope Science Institute collec-tion of guide star digital plate scans. The estimated uncer-tainty of positions from the Guide Star Catalog images is

(Russell et al. 1990) and results from variations in0A.2È0A.8plate characteristics and edge e†ects. The positions listed inthe table have, therefore, been rounded to the nearest 0.1 sof time in right ascension and in declination.0A.1

The SIMBAD database was searched to identify anycorrelations between the UV-bright sources present in thiswork with previously identiÐed objects. A radius of 5@around each position listed in Table 1 was used in thesearch. Corresponding identiÐcations, along with relevantcolor information, are included in the table. The SIMBADsearch was completed on a database updated e†ective 1999June.

3. THE FINDING CHARTS

Finding charts are reproduced from FITS imagesextracted from the STScI GASP system and have been pro-vided for all UV-bright sources listed in Table 1 and Figures1È7. These images were Ðrst retrieved from the guide starimage archive and converted to GIF format. The imageswere then imported into Framemaker for placement ofidentiÐcation marks for each of the sources and creation ofeach page of charts presented in the Ðgures. The scale for allcharts is approximately 11 arcsec mm~1, with a full Ðeld of8@ on a side. All charts are displayed with north up and eastto the left.

4. DISCUSSION

Some of the more interesting objects found are discussedbelow. One source, Lanning 82 (Paper I), was recoveredduring the examination of an adjacent overlapping platescanned in the current work. This source was conÐrmed tobe the previously identiÐed white dwarf WD 2124]550(McCook & Sion 1987). The estimated U[B color waswithin 0.1 mag of that originally determined for Lanning 82(U[BD [0.4) ; the B magnitude was estimated at D14 inPaper I, but at D15 on the overlapping plate. SIMBADlists several additional estimates which consistently fallaround BD 14.7 and U[BD [0.68. Although the spreadin B is slightly beyond the 0.5 mag uncertainty quotedearlier, this source is not believed to be variable.

Two other recoveries of previously identiÐed whitedwarfs are noted below. No attempt was made prior toscanning the plates to identify known white dwarfs or otherpeculiar UV-bright sources. Only after accurate positionsand magnitude and color estimates were completed for all

2000 PASP, 112 :251È263

262 LANNING & MEAKES

sources were correlations conÐrmed using informationreturned from the SIMBAD literature search.

L anning 361.ÈThis source is coincident with the pre-viously identiÐed DA white dwarf found by Downes (1986),KPD 2046]3940 (DAw). Both the B magnitude and U[Bcolor fell within the 0.5 mag uncertainty for this very bluesource. Downes gave an estimate of U[BD [1.20 ; theestimate from this study was D[0.9.

L anning 430.ÈWD 2119]58 (DA) is the third whitedwarf recovered during this part of the survey analysis.McCook & Sion (1987) list the white dwarf as a DA6 with aphotographic B mag of 16.0. The B and U[B estimatesdetermined in this study are 17.0 and [0.5, respectively.

Among the list of interesting objects found and examinedfor this paper were two marginal UV sources located in theÐelds of cataloged X-ray sources.

L anning 390.ÈEstimated at andmBD 11.0

U[BD [0.3, this source is within 2@ of the reported posi-tion of the transient X-ray source Cyg X-4. However, theposition for Cyg X-4 is very uncertain given the 1 deg2 errorbox (Amnuel, Guseinov, & Rakhamimov 1982). Threerocket observations are listed by Amnuel which suggest aslow decline of the X-ray source of about a factor of 8 in 3years. The X-ray source has not been seen since the lastobservation in 1968 (Amnuel, Guseinov, & Rakhamimov1979). It seems highly unlikely that an 11th magnitude starclose to the center of the error box would not have beenobserved during previous searches for the optical counter-part to the X-ray source. No optical candidate for Cyg X-4has ever been identiÐed.

L anning 456.ÈLocated in the Ðeld of the transient X-raysource H2116]55. The X-ray source, detected in 1978 withHEAO 1, was a transient event which lasted about 200 s(Connors, Serlemitsos, & Swank 1986). Although the posi-tion of the UV source is within 5@ of the center positionreported for the X-ray source, the position is not well deter-mined. Based upon the intensity of the X-ray source eventand optical Ñare statistics, Conners et al. indicated thesource was likely to be a dMe or dKe star undergoing astrong Ñaring episode. If so, the correlation of Lanning 456with the X-ray source is purely coincidental and cannot beconÐrmed as the optical identiÐcation of the X-ray source.

A number of marginal UV sources were included whichcorrespond to members of the young open cluster Trumpler37 located at the nucleus of the Cep OB2 association IC1396. This cluster contains several O- and B-type stars(Weikard et al. 1996) as well as numerous later type stars.Two of the UV sources detected are noted by SIMBAD tobe F8 stars, while one is a G2 star. All three stars are mostlikely blue metal-poor subdwarfs. As noted by Wildey et al.(1962) and Bond (1970), metal-poor subdwarfs may exhibita signiÐcant color excess in the ultraviolet due to the lack ofline-blanketing e†ects. Often, such subdwarfs are associatedwith high-velocity and high proper motion stars (Eggen,

Lynden-Bell, & Sandage 1962). The sources identiÐed inthis study were, of course, only detected by virtue of theassociated U[B color. Eight UV sources in all were identi-Ðed by the SIMBAD literature search to be members of theTrumpler 37 cluster including Lanning 409, 410, 414, 425,426, 427, 434, and 438. Table 1 provides the correspondingTrumpler cluster member identiÐcation as well as the spec-tral type where available.

In order to assure ourselves we did not miss any UV-bright sources in Trumpler 37 which should have beendetected, we examined all available UBV data for Trumpler37 sources resident in the database provided by Jean-Claude Mermilliod, the WEBDA site devoted to stellaropen clusters.2 Of the 73 stars with U[B\ [0.01 or bluer,35 are brighter than B\ 10.0 (our upper limit), and anotherseven are in the marginal range close to the upper limitwhich could prevent reliable detection due to merging ofimages. Another 29 stars are in the color range of U[B\ 0to U[B\ [0.34. Sources in this range are subject to mar-ginal detection due to the uncertainty in magnitude esti-mates, calibration of the eye versus published magnitudesand colors, distortions of the images, and potentiallymerged images of fainter stars in crowded Ðelds. Thus, onecannot reliably expect to identify sources with U[B colorsin this range. Only two sources from the list of photogra-phic UBV magnitudes by Kun (1986) remain, 3209 and4029. Star 4029 (V \ 14.4) is coincident with Kun 29 and islisted as U[B\ [0.57. Kun notes the star is variable,which could explain why it was not detected in this survey.Also, the accuracy of colors quoted by Kun from the colortransformations are 0.2 mag in the U and 0.1 mag in the B.Star 3209 (V \ 15.7) is listed by Kun as U[B\ [1.0, buta B[V \ 2.17. These colors are clearly anomalous withmagnitudes extending beyond the calibration sequence usedby Kun and are, therefore, highly suspect.

L anning 362.ÈWhile no central star was evident in thissource, identiÐed with the planetary nebula PNG078.9]00.7, the nebula itself appeared slightly blue andwas, therefore, included in the list of UV sources.

L anning 415.ÈThis UV-bright source is identiÐed as the1.6 day period eclipsing b Lyrae type binary DL Cep.Kukarkin et al. (1971) list the V -magnitude ranges from12.4 to 13.2. The B-magnitude estimate in this study was11.2 (U[BD [0.5).

L anning 420.ÈThe estimated B magnitude for this sourceis D17.2, with a U[BD [0.72. However, when the Digi-tized Sky Survey was examined, no evidence of the sourcecould be found suggesting the possibility the source ishighly variable, or perhaps an old nova. Similar objectshave been found and reported during analysis of other

ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ2 The WEBDA home page is located at http ://obswww.unige.ch/

webda/webda.html.

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FINDING LIST OF UV-BRIGHT STARS. V. 263

Sandage two-color plates previously, e.g., Lanning 17(Paper I) and Lanning 302 (Paper IV). The epoch of theplate on which Lanning 420 was identiÐed wasJ.D.\ 2,440,560.6177.

Two previously known white dwarfs coincident withplates examined in this work were not detected as UVsources. The DA2 white dwarf WD 2028]390 was noted bySchwartz (1972) to have a B[V \ [0.33 andU[B\ [0.98 based upon photoelectric photometryobtained in that study. Greenstein (1984) gives a B[Vvalue of [0.31 from spectrophotometric observations.Downes (1986) detected the white dwarf as a UV sourceindicating his colors were consistent with previouslypublished values. However, when examined on the associ-ated Sandage two-color plate, the white dwarf was notselected as a candidate because of the very marginal color,estimated at D0.0 to [0.1 at best. Although a slight platebalance o†set of D[0.3 in the U[B was evident on theSandage survey plate, other sources on the same plate, e.g.,Lanning 361 noted above, were well within the quoteduncertainty of D0.5 mag. No reports of variability forWD 2028]390 were found in the literature, leaving us withan unexplained large discrepancy in the U[B color.

The white dwarf WD 2101]398\EGGR 501 was alsonot detected in this study. It is, however, classiÐed as a DC9and was included in the Greenstein (1979) list of red degen-

erate stars. This white dwarf is red and was found only byvirtue of its proper motion.

We would like to thank Dr. Allan Sandage for theopportunity to pursue the examination of his two-colorsurvey. We would also like to thank Dr. Steve Drake,HEASARC, for providing helpful information and refer-ences for the transient X-ray sources discussed in this paper.Discussions with Drs. Richard Green (NOAO) and D. J.MacConnell (CSC/STScI) regarding the metal-poor sub-dwarfs were very useful and appreciated. Thanks also to Dr.Jean-Claude Mermilliod for assistance in navigating theWEDBA database on open clusters. Finding charts wereobtained using the Guide Star Astrometric SupportProgram developed at the Space Telescope Science Insti-tute. The original photographic survey was supported inpart by the National Aeronautics and Space Adminis-tration under grant NGR 09-140-009. This research projectwas supported by funding from the STScI, which is oper-ated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555, andmore recently by the NASA ADP contract PO S-92513-Z.We have also made use of the SIMBAD database operatedat CDS, Strasbourg, France, for the literature search andcollection of source identiÐcation information.

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