Planetary Nebula Central Stars and Symbiotic Stars in the MACHO Galactic Bulge Database

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1 PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 122: , 2010 May The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A. Planetary Nebula Central Stars and Symbiotic Stars in the MACHO Galactic Bulge Database JULIE LUTZ, OLIVER FRASER, JEANNE MCKEEVER, AND DEBORAH TUGAGA Department of Astronomy, University of Washington Seattle, WA ; Received 2009 September 11; accepted 2010 March 9; published 2010 April 22 ABSTRACT. We have examined central stars of planetary nebulae and symbiotic stars found in the MACHO Galactic bulge database to look for variability. We found four central stars of planetary nebulae and eight symbiotic stars that show variability. We examine the variability and the nature of these objects in detail, as well as reporting on the objects that we did not find to be variable. 1. INTRODUCTION Among planetary nebulae (PN), a few with binary central stars are known, but it is important to discover as many binary central stars as possible in order to evaluate the role that binaries play in shaping the morphologies of PN (Schwarz & Monteiro 2004; Sorensen & Pollacco 2004; de Marco 2009). We looked to the MACHO Galactic bulge (MGB) database (Alcock et al. 1997) as a source of information that might lead to the discovery of new variable (and possibly binary) planetary nebula central stars (PNCS). Because most Milky Way PN are concentrated toward the plane of the Galaxy, it seemed reasonable that we would find quite a few PNCS in the MGB fields. This turned out to be the case. Of 74 PNCS that we identified in the MGB database, four exhibited some sort of variability. We discuss these stars and provide MACHO V and R magnitudes for all of the nonvariable PNCS that we found. A few of the known symbiotic stars (SS) are found in the MGB fields. We decided to investigate these also. Presumably all SS are binary systems because of their composite spectra (G M star plus emission lines). We were curious to look at the long-term variability of any SS that we found in the MGB database because the variability of SS is well characterized only for brighter members of the class. We wanted to find out what sorts of long-term fluctuations in brightness were observed by the MACHO project. Would there be Mira-like variability, sudden outbursts, or other phenomena that have been shown by the brighter SS? We will discuss the eight SS that we found to be variable. 2. DATA The MACHO project (Alcock et al. 1997) comprises observations taken over an 8 yr period of the Large and Small Magellanic Clouds and the bulge of the Milky Way. Our sample of PNCS is drawn from both the MACHO variable star catalogs 1 and the full database of detected sources. Sources from the full MACHO database of millions of objects were selected for the MGB Variable Star Catalog if the central 80% of points in the object s light curve failed to fit a constant magnitude in a χ-square test. This criterion resulted in 521,007 candidate variables in the Galactic bulge. 2 MACHO data were taken simultaneously in two nonstandard filters: red and blue. These can be transformed to Cousins V and R using the method of Bessell & Germany (1999), which was calibrated for metal-poor giants. We present these magnitudes here in the interest of providing rough estimates. When we only have data in one MACHO band, we assume a color of 0 for PNCS and 1 for SS V ¼ 24:114 þ 1:00258 B MACHO 0:153 ðb MACHO R MACHO Þ R ¼ 23:944 þ 1:00444 R MACHO þ 0:184 ðb MACHO R MACHO Þ: Figure 1 shows the MACHO blue and red light curves normalized to V and R for the periodic PNCS Hf 2-2; the typical MACHO errors, measured from the folded light curve, are less than 0.1 mag. MACHO employed a nonparametric phasing technique known as the SuperSmoother method (Reimann 1994) to phase all of the light curves in the MGB Variable Star Catalog. This technique is robust against complex light-curve morphology, but fails when presented with strongly multiperiodic behavior or when the periodic signal is very weak. In this work we utilize the CLEANest algorithm of Foster (1995, 1996a, 1996b) to determine the frequency characteristics of the stars in our sample. 1 VizieR Online Data Catalog, 2247 (C. Alcock et al., 2003). 2 The MACHO Project is online at 524

2 PN CENTRAL AND SYMBIOTIC STARS IN MACHO 525 FIG.1. PN Hf 2-2, which shows an 0: :00001 day period. Magnitudes, like those in Fig. 2, are MACHO blue and red normalized to our estimated V and R. See the electronic edition of the PASP for a color version of this figure. As implemented by Rorabeck (1997), and described in Alcock et al. (1999), CLEANest uses the robust date-compensated discrete Fourier transform (DCDFT) algorithm of Ferraz-Mello (1981), which finds accurate estimates of the amplitudes of the Fourier spectrum for data with uneven time sampling. The CLEANest algorithm iteratively finds the most significant peaks in the power spectrum from the DCDFT. In this article, we searched a frequency space of 0:0003 day 1 to 10 day 1 (corresponding to periods from one-tenth of a day to 3333 days) with a frequency spacing of 0:00003 day 1. We used the online versions of two PN catalogs (Kohoutek 2001; Acker et al. 1992) to identify PN that might fall within the MGB fields. We entered the coordinates of the candidate PN into the MGB Variable Star Catalog and usually found a star within 2 of the PN 2000 coordinates. We used photographs of nebulae and previously-published data on magnitudes of central stars as guides to make sure we were getting the correct star, especially since these are very crowded fields. Results for the PNCS we found are given in Tables 1 and 2 and in Figures 1 and 2. Not every PN that we thought might have a central star observed in the MGB fields turned out to be there. There are gaps between some of the MGB fields where no data were taken. Also, occasionally an object right on the edge of a field was missing. In addition, some PNCS could be too faint for detection in the MACHO survey. Indeed, we found occasionally that data existed in one MACHO filter but not the other, usually due to faintness issues. In Table 3 we list 11 PNCS that we did not find in the MGB database. We selected SS candidates from the catalog of symbiotic stars compiled by Belczyński et al. (2000). A total of 17 candidates were investigated. Thirteen SS were found in the database and analyzed for variability. Results for these stars are found in Tables 4 and 5 and Figures Four SS were not TABLE 1 VARIABLE PLANETARY NEBULA CENTRAL STARS PN G Name FTS ( ) V R Notes H Irregular M Irregular M Irregular, and possibly other variability Hf ± day period a Distance to nearest MACHO object.

3 526 LUTZ ET AL. TABLE 2 PLANETARY NEBULA CENTRAL STARS THAT DID NOT SHOW VARIABILITY PN G (PK) Name FTS ( ) V R Notes Bl No variability H No variability SB No variability M No variability M No variability KFL No variability SB No variability M No variability M No variability M No variability H No variability Bl No variability M No variability SB Insufficient data ShWi Possible variability ShWi No variability ( ).... ShWi No variability ( ).... ShWi No variability ( ).... ShWi No variability ( ).... ShWi No variability SB No variability SB Insufficient data H No variability ShWi No variability M Insufficient data KnFs No variability M No variability H No variability M Possible variability Sa Possible variability M No variability KnFs No variability M No variability M No variability Pe No variability H Possible variability KnFs No variability M Insufficient data Ap Insufficient data SB Insufficient data KFL No variability H Insufficient data NGC Insufficient data M No variability M Insufficient data H No variability H Insufficient data Pe Insufficient data H No variability SB Insufficient data SB Insufficient data H No variability H No variability SB Insufficient data SB Insufficient data M No variability H No variability KnFs No variability NGC Insufficient data

4 TABLE 2 (Continued) PN G (PK) Name FTS ( ) V R Notes MaC Possible Variability Pe No variability SB Insufficient data H No variability Ae No variability Vy No variability M No variability ( ).... SP No variability H Possible variability MaC No variability M No variability a Distance to nearest MACHO object. PN CENTRAL AND SYMBIOTIC STARS IN MACHO 527 found for the same sorts of reasons discussed for the PN, and these are listed in Table RESULTS 3.1. Planetary Nebulae We found only one PNCS (Hf 2-2) that exhibited periodic behavior. Hf 2-2 had actually been studied by one of us before (Lutz et al. 1998), and the preliminary study is confirmed by our more detailed analysis. Three other PNCS appear to have irregular variations. All of these PNCS and their nebulae are discussed in the next section. Their variations are displayed in Figures 1 and 2 and in Table 1. The columns in Table 1 give the PN G number (or PK number in parenthesis), a common name for the PN, the MACHO FTS number (used to find the object in the MACHO database), the distance (in ) between the catalog coordinates of the PN and the MACHO object, the median V and R magnitudes for the object, as derived from the MACHO data (see 2), and a note about the type of variability observed. Most of the PNCS were not found to exhibit variability based upon the available MACHO data. A list of the PNCS that we were able to identify but were not found to be variable is given in Table 2, with a note explaining why the PNCS was not confirmed to belong in the variable category. Out of 74 PNCS that we found in the MACHO database, 4 exhibited some type of variability, 47 exhibited no variability, and 17 had insufficient data for a judgment on their variability. The remaining 6 exhibited possible variability, noted as such in Table 2. A few PNCS that we had hoped to find in the MACHO database were not there. These are listed in Table 3 for completeness Discussion of Individual Planetary Nebulae Hf 2-2 was discovered to be a variable PNCS in a preliminary survey of the MACHO database done by Lutz et al. (1998). Their finding of a period of 0.40 days, with an amplitude of 0.11 mag in blue and 0.13 mag in red, is confirmed by this study. The MACHO red and blue filter observations and the observations phased to a day period are shown in Figure 1. The variability likely comes from heating effects in a binary system. Hf 2-2 is a particularly interesting PN. According to Liu et al. (2006), the optical spectrum of the PN has many strong heavymetal recombination lines. The optical recombination lines appear to arise from regions in the nebula that are about 10 times cooler (about 900 K) than the regions where the collisionallyexcited emission lines such as those of [O III] arise. The appearance of the nebula is unremarkable. It is round with a diameter of about 20 in both [O III] and Hα (Schwarz et al. 1992). H 1-54 s central star shows a dropout variability in the MACHO red magnitude at the level of about 2 magnitudes, as shown in Figure 2. The star has a MACHO red magnitude of about 15 most of the time, but occasionally it dims suddenly. Unfortunately no data are available in the blue. No periodic behavior is evident in the variations. The nebula has a diameter of 2, as measured from a Hubble Space Telescope (HST) Hα archival image (Bensby & Lundström 2001). The nebular abundances are typical for a bulge PN (Wang & Liu 2007; Chiappini et al. 2009). Kaler & Jacoby (1991) found a Zanstra temperature of 35,000 K for the central star. The nebula is low-excitation. M 2-29 is a particularly interesting PN in several respects. Hajduk et al. (2008) reported an apparent dimming and rebrightening of the central star based upon OGLE data and confirmed by our MACHO observations. We reproduce the MACHO light curve in Figure 1, which is labeled M 2-29a. Hajduk et al. (2008) attribute the variation in the light curve to dust formation and dissipation. In addition to the object with the dramatic dimming in brightness, we found a very nearby object in the MACHO database which is labeled M 2-29b in Figure 1. This object is about 0.5 from the central star and thus would be within the nebula, which has a diameter of about 4, as seen on both Hα and [O III] HST images (Hajduk et al. 2008). M 2-29b also looks somewhat variable, and this variability may be related to the dust event that is seen so dramatically in the observations of the central star.

5 528 LUTZ ET AL. FIG. 2. PN showing irregular variability. Blue (blue crosses) and red (red dots) light curves with the MACHO magnitudes normalized to our V and R estimates. All magnitudes presented in this article are MACHO blue and red magnitudes normalized to the V and R found using the transformations in 2. MJD (modified Julian Date) is JD 2,400, Miszalski et al. (2009) reached quite different conclusions about the nature of M They found this object to be variable, but viewed it as a possible SS rather than a PN. If it is a SS, it is one of a very small number of these objects that has a nebula. They did not discuss the nature of the variability, as their article was on binary PNCS. M 2-29 is a PN with extremely low abundances of C, N, O, Ne, Ar, and S (Pena et al. 1991; Exter et al. 2004). It is a mediumexcitation PN with an atypically high electron temperature of 20,000 K (Exter et al. 2004). The Is it a PN or a SS? conundrum is one that arises occasionally when dealing with these two types of objects (Lutz 1977; López et al. 2004; Arrieta et al. 2005). Miszalski et al. (2009) cite a paper by Gutierrez-Moreno et al. (1995) which attempts to distinguish between SS and PN by using the relative strengths of [O III] emission lines. There is ambiguity in using this criterion. High-density PN can overlap with low-density SS with regard to their line ratios. TABLE 3 PLANETARY NEBULA CENTRAL STARS NOT FOUND PN G Name ( ) Notes SwSt H H MACHO source is nearby variable B0Ib star M M KnFs M KnFs H M SB a Distance to nearest MACHO object.

6 TABLE 4 VARIABLE SYMBIOTIC STARS PN G (PK) Name FTS ( ) V R Notes CnMy Variable in blue SS Variation in blue ( )..... H day period V2506 Sgr Variable, with a 913 day period SS Long, possibly periodic, variation Hen Dimming and return in 100 day light curve Hen Variation visible in blue... Hen day period, possibly other periods a Distance to nearest MACHO object. PN CENTRAL AND SYMBIOTIC STARS IN MACHO 529 However, colors from the Two Micron All Sky Survey (2MASS; Skrutskie et al. 2006) of ambiguous objects can be helpful for some cases. The 2MASS source ( ) closest to the coordinates of M 2-29 has J H ¼ 0:4 and H K ¼ 1:2, which places it in a realm of the J H versus H K color-color diagram occupied uniquely by planetary nebulae (Phillips 2007). The present study addresses only the optical variability of the central star of M 2-29, but we suspect it should be kept in the category of planetary nebula. M 1-44 (PN G ) has been classified as a PN by some groups and as a SS by others. It is listed in the catalog of symbiotic stars compiled by Belczyński et al. (2000) under its alternate name of He There is a nebula with a size of 6.0 by 5.4 (Tylenda et al. 2003) offset slightly from the red star that is the subject of the MACHO observations. Lutz & Kaler (1983) found a red star of spectral type K2 III offset by about 2 from a low-excitation nebula. The spectrum of the nebula showed emission lines and very little continuum. Lutz and Kaler s hypothesis was that there are two separate objects which just happen to be close together in the sky: a low-excitation nebula and a K-type giant star. However, the image obtained by Schwarz et al. (1992) shows that the nebulosity encompasses two stars that are quite close together. Further information about the nature of M 1-44 might be gleaned from investigating the 2MASS colors of the object (Skrutskie et al. 2006). The 2MASS source closest to the coordinates given for the PN ( ) has colors (J H ¼ 0:7, H K ¼ 0:2) and thus falls in an area of the color-color diagram that is occupied both by late-type giant stars and by some PN (Phillips 2007). 2MASS sources that are quite nearby ( and ) also have J H and H K colors that place them in a similar area of the color-color diagram. Hence, the near-infrared colors do not provide any information that elucidates the nature of M According to Exter et al. (2004), the spectrum of the nebula exhibits emission lines of atoms with relatively low ionization levels such as strong [O II] and [N II] lines and no [O III]. They find a nebular electron density of 10 2:6 cm 3. This result is in approximate agreement with that of 10 3:2 cm 3 found from the [S II] lines by Stanghellini & Kaler (1989). Luna & Costa (2005) quoted the electron density of the nebula as 10 8 cm 3 based upon the absence of [O III] emission lines. However, since the [O III] emission lines 4959 Å and 5007 Å are not present in their table of spectral line intensities and the [N II] and [S II] lines are strong, the low densities quoted by other authors are likely valid. The low electron density is evidence that M 1-44 is a PN. The MACHO data on M 1-44 indicate that the object is brighter in the red than in the blue, as shown in Figure 2. The red magnitude was generally about 12.6 and the blue magnitude about It showed brightness excursions of about a magnitude in the red filter, but variations in the blue magnitude were observed only during the third MACHO observing season. No periodic behavior was found. TABLE 5 OTHER SYMBIOTIC STARS FOUND IN DATABASE BUT NOT VARIABLE PN G (PK) Name FTS ( ) V R Notes ( )..... AP Possible variability AS No variability V 4018 Sgr Possible variability ( )..... Hen Insufficient data V3929 Sgr a Distance to nearest MACHO object.

7 530 LUTZ ET AL. FIG. 3. Symbiotic star CnMy 17. See the electronic edition of the PASP for a color version of this figure. Our conclusion based upon the observations available so far is that M 1-44 is a PN with a late-type (and thus presumably binary) central star. Radial velocity observations of the nebula and the cool star would be desirable to establish association Symbiotic Stars Symbiotic stars are binaries that pair a cool star (usually M-type, but some are spectral types F K) with a hot star (usually a white dwarf). Sometimes the M-type star is a Mira variable. FIG. 4. Symbiotic star SS See the electronic edition of the PASP for a color version of this figure.

8 PN CENTRAL AND SYMBIOTIC STARS IN MACHO 531 FIG. 5. Symbiotic star H The blue light curve is phased to the period found in the red light curve, which has the best-fit period of 397 days; note that the observed variation lags and returns to the fit in this 2500 day light curve. The variation in the red light curve is approximately 3 times greater than the similar variation in the blue light curve. See the electronic edition of the PASP for a color version of this figure. Depending upon the sizes of the stars and the characteristics of the orbit, there is a wide variety of possible interactions between the two stars. Some symbiotic stars exhibit emission line spectra with very high ionization levels, while others have only mediumexcitation spectra. A few have spectra with a wide range of ionization potential emission lines. Some symbiotic stars show FIG. 6. Symbiotic star V2506 Sgr. See the electronic edition of the PASP for a color version of this figure.

9 532 LUTZ ET AL. FIG. 7. Symbiotic star SS See the electronic edition of the PASP for a color version of this figure. the variability of a Mira star, while others are not known to vary at all. The more active symbiotic stars can have sudden irregular outbursts of several magnitudes, whole others brighten and fade slowly but with no particular cadence. Symbiotic stars are rare. There are only 218 entries in the symbiotic stars catalog published by Belczyński et al. (2000) and 13 of them fall within the MACHO Galactic bulge fields. In examining the MACHO Galactic bulge data on known symbiotic stars, we were looking for several possible types of variation: First, the variability characteristic of a Mira star, FIG. 8. Symbiotic star Hen See the electronic edition of the PASP for a color version of this figure.

10 PN CENTRAL AND SYMBIOTIC STARS IN MACHO 533 FIG. 9. Symbiotic star Hen Although the light curves are dominated by noise, there is a long-term variation of 0.2 mag visible in the blue. See the electronic edition of the PASP for a color version of this figure. which occurs on timescales of months to years. Second, outbursts of several magnitudes that occur at visible (and other) wavelengths over timescales of a few months (e.g., RS Oph). Third, relatively slow (months to years) brightening and fading that does not look at all like Mira variability (e.g., BF Cyg). Fourth, erratic smaller outbursts over weeks to months such as occur in AG Dra. We found some Mira-type variability in symbiotic stars where it had not been documented before. We also found a couple of stars with irregular variability on the order of a magnitude or so. No major dramatic outbursts FIG. 10. Hen Note the evidence of another period at phases See the electronic edition of the PASP for a color version of this figure.

11 534 LUTZ ET AL. TABLE 6 SYMBIOTIC STARS NOT FOUND PN G (PK) Name ( ) V3804 Sgr V4074 Sgr ( )... Hen ( )... Ap a Distance to nearest MACHO object. were found. The eight stars that showed variability will be discussed individually. Basic data for them are given in Table 4 and the light curves are given in Figures We were also looking to confirm the extent to which symbiotic stars are quiet, i.e., do not show optical variability. The long time frame of the MACHO monitoring provides a good indication that some symbiotic stars are indeed not variable on timescales of a few years. We found one star (AS 281) that had no apparent variability, two that might have some small irregular variability, and one that had insufficient data. These four objects are listed in Table 5. As with the PNCS, there were a few SS that we did not find in the MACHO database for reasons discussed in 2. These are listed in Table Discussion of Individual Symbiotic Stars HD (CnMy 17) has only one season of MACHO observations. The star is clearly variable in the blue, but it is impossible to tell whether or not it is periodic because of the limited data stream. In the red, the magnitudes are scattered. The object looks variable in the red, but the variations appear to be irregular. The cool star in the system is an M3 giant (Zamanov et al. 2007). Luna & Costa (2005) derived N/O, Ne/O and Ar/O abundances from the emission line spectrum of HD , so the spectrum must be fairly typical of a high-excitation symbiotic star. Van Winckel et al. (1993) observed only Hα emission in the spectrum of this SS in their study of line profile shapes, which included [O III] and He I lines. The line shape at the time of their observations was single-peaked. SS exhibits irregular variability in both the blue and red filters. The MACHO blue magnitude is generally about 13.6, but dropped to as low as about 14.7 during the observation period. The red magnitude was usually at 12.2, but variations significantly above and below that magnitude were observed. SS has only emission lines of H I, He I, and He II in its spectrum (Munari & Zwitter 2002), and the cool giant in the system varies in spectral type between K5 and M0 (Zamanov et al. 2007; Mikolajewska et al. 1997). It is a D-type symbiotic (Belczyński et al. 2000). The variability can only be characterized as irregular in both the blue and red magnitudes. H 2-38 is a well-known D-type symbiotic star with very high-excitation emission lines, including strong [Fe VII] (Belczyński et al. 2000; Munari & Zwitter 2002). Gromadzki et al. (2009) recently published a pulsation period of 395 days for the Mira variable present in the system, based upon OGLE data. Figure 5 shows the MACHO blue and red light curves, as well as our best-fit period for the red light curve: 397 days. It is evident that the observed periodicity varies slightly from cycle to cycle. The blue light curve is phased to the period found in the red light curve. Observations near the brightness maximum are particularly scarce. V2506 Sgr is a S-type symbiotic with a giant star varying between spectral types M0 and M5.5 and a very high-excitation emission line spectrum (Mikolajewska et al. 1997; Mürset & Schmid 1999). The infrared colors published by Phillips (2007) fall in a region of the symbiotic star J H versus H K diagram where Mira variables are usually found. The MACHO data are consistent with a 913 day overall period of variation with a shorter period variability of 90 days superimposed. The superimposed fluctuations occur over timescales of weeks to months. The MACHO blue light curve and the light curve phased to a period of 913 days are shown in Figure 6. SS has a high-excitation emission line spectrum (Munari & Zwitter 2002) with a M7 star (Mürset & Schmid 1999). The 2MASS infrared colors put SS in the realm of the Mira variables (Phillips 2007). The variability of this S-type symbiotic system has not been studied previously. We find a long, possibly periodic variation which is shown in the plots in Figure 7. Hen has only a short stream of MACHO observations, which are shown in Figure 8. The star dims by about 0.3 mag and returns to its previous brightness in about 100 days. This S-type symbiotic star was observed to have an M0 giant and a medium-excitation ([O III] being the highest ionization potential species observed) emission line spectrum by Mikolajewska et al. (1997). Hen is included among the variable SS because its MACHO blue light curve showed a downward trend over several observing seasons. In addition, there is considerably more scatter in the blue data as compared to the red data. Since the star is fairly bright, the scatter in the blue observations well exceeds the error bars. This sort of variability was found by Hedrick & Sokoloski (2004) in the Johnson B filter observations of Hen They observed variations on the order of 0.1 mag in B (but not in V ), which they attribute to variations in the accretion disk of the symbiotic system. Hen has a K1 III star and is classed as both an S and a D symbiotic (Belczyński et al. 2000). This means that the infrared shows signatures of both warm dust and the cool star. The emission line spectrum does not show extremely high excitation lines, but species such as [O III] and He II are present (Munari & Zwitter 2002).

12 PN CENTRAL AND SYMBIOTIC STARS IN MACHO 535 Hen is a S-type symbiotic whose M5 star has the distinction of a very large rotational velocity for its spectral class 52 km s 1 (Zamanov et al. 2007). The emission line spectrum has lines of a variety of excitation potentials (Munari & Zwitter 2002). The optical variability of this object has not been studied previously, although the 2MASS infrared colors of J H ¼ 1:1 and H K ¼ 0:5 indicate that a Mira variable is likely to be present (Phillips 2007). We find a period of approximately 1003 days from both the blue and red light curves. As was the case for V2506 Sgr, the light curve appears to have many minor wiggles superimposed on the main variation. 4. SUMMARY We have confirmed the variability of the central star of Hf 2-2 and argued that several other PNCS might be irregular variables. For objects that have dual identifications as PN and SS, we have attempted to use currently available evidence to classify them. For the SS, we found some Mira-type variability and some variations superimposed on Mira-type light curves. We also found irregular variability of just a few tenths of magnitude. We did not find any dramatic outbursts of several magnitudes. Both the variable PNCS and the SS are of diverse types. In the case of the PNCS, the surrounding nebulae are of various shapes and the stars have a wide range of temperatures. The variable SS are a mixture of S- and D-types and their emission line spectra are of diverse excitation classes. This paper utilizes public domain data obtained by the MACHO Project, jointly funded by the US Department of Energy through the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48, by the National Science Foundation through the Center for Particle Astrophysics of the University of California under cooperative agreement AST , and by the Mount Stromlo and Siding Spring Observatories, both part of the Australian National University. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, and funded by the National Aeronautics and Space Administration and the National Science Foundation. Thanks go to the Kenilworth Fund of the New York Community Trust for support of undergraduate students and for funding page charges. 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