Comparison Stars Research Articles

ι Orionis—Evidence for a Capture Origin Binary

The star ι Ori (HD 37043, HR 1899) is a 29.1338 day period, double-lined O-type spectroscopic binary with a highly eccentric orbit. The classification of the primary (O9 III) is well established. The secondary, roughly 2 mag fainter, is generally acknowledged as an early-type B star, but claims about its luminosity class have been made only from its estimated light contribution and not from its spectrum. We have collected visual data with the 1 m Multiple-Telescope Telescope (MTT; at the Center for High Angular Resolution at Georgia State University) in four wave bands well distributed in orbital phase, with the periastron passage particularly well covered. We present reconstructed component spectra from our tomographic reconstruction technique. According to three Morgan-Keenan (MK) luminosity criteria, we can unambiguously characterize the secondary as a B1 III-IV giant (MK type or B0.8 III-IV interpolated type). We also have constructed three line-strength indices from eighteen observed individual lines for the secondary and a grid of comparison stars. These results confirm the typing from the MK luminosity criteria. Furthermore, we argue, from the mass ratio (q = 0.5), evolutionary considerations, the orbital scale, and the unremarkable CNO element equivalent widths of the secondary, that this system is not coevolved nor has it undergone significant mass transfer. We postulate an origin for the system in a binary-binary collision and suspect that the runaway stars μ Col and AE Aur may have been the original partners for the current ι Ori secondary and primary, respectively.

On the rotation period of Capella

We present differential Hα and Hβ photometry of the very bright RS CVn-binary α Aurigae (Capella)obtained with theVienna automatic photoelectric telescope in the years 1996 through 2000. Low-level photometric variations of up to 0m.04 are detected in Hα. A multifrequency analysis suggests two real periods of 106 ± 3 days and 8.64 ± 0.09 days, that we interpret to be the rotation periods of the cool and the hot component of the Capella binary, respectively. These periods confirm that the hotter component of Capella rotates asynchronously, while the cooler component appears to be synchronized with the binary motion. The combined Hα data possibly contains an additional period of 80.4 days that we, however, believe is either spurious and was introduced due to seasonal amplitude variations or stems from a time-variable circumbinary mass flow. The rotational periods result in stellar radii of 14.3 ± 4.6 R⊙ and 8.5 ± 0.5 R⊙ for the cool and hot component, respectively, and are in good agreement with previously published radii based on radiometric and interferometric techniques. The long-period eclipsing binary Aurigae served as our check star, and we detected complex light variations outside of eclipse of up to 0m.15 in H α and 0m.20 in Hβ. Our frequency analysis suggests the existence of at least three significant periods of 132, 89, and 73 days. One of our comparison stars (HD 33167, F5V) was discovered to be a very-low amplitude variable with a period of 2.6360 ± 0.0055 days.

On the δ Scuti variability in the pre-main sequence Herbig Ae star HR 5999

A reanalysis of photometric data for the bright, southern Herbig Ae star HR 5999 obtained by Praderie et al. (1991) at ESO in 1985 shows Scuti pulsation with the same period, 4.812 d 1 , and semi-amplitude, 6 mmag, found by Kurtz & Marang (1995) in data obtained from SAAO in 1994. HR 5999 is, therefore, a potential candidate to test Breger & Pamyatnykh's (1998) predictions of evolutionary period changes 10 to 100 times faster in pre- main sequence Scuti stars than in post-main sequence stars. We argue that the low frequency, low amplitude 2 CVn variability of HR 6000 with a period near 2 d, and its long-term variability are no hindrance to using it as a comparison star for study of the Scuti variability of HR 5999. With a separation of 44 arcsec between HR 5999 and HR 6000, and similar brightnesses for the two stars, we urge the use of small telescopes with CCD photometers to obtain the long-term data necessary for the study of period change. We point out that this can be done under less-than-ideal photometric conditions and urban lighting with CCD photometers on small telescopes which are widely available at small observatories, at universities and at the home observatories of serious amateur astronomers.

Chandra,EUVE,HST, and VLA Multiwavelength Campaign on HR 1099: Instrumental Capabilities, Data Reduction, and Initial Results

In mid-September of 1999, a multiwavelength campaign was carried out on the coronally active RS Canum Venaticorum binary HR 1099 (K1 IV + G5 V; P = 2.84 days), during commissioning of the High Energy Transmission Grating Spectrometer (HETGS) of the Chandra X-ray Observatory (CXO). The coordinated program involved the Extreme Ultraviolet Explorer (EUVE), the Hubble Space Telescope Imaging Spectrograph (STIS), and the Very Large Array (VLA). The objective was to study the system in quiescence, across as much of the electromagnetic spectrum as practical, and to catch any flares that might occur. The EUVE 80-180 A light curve of HR 1099, covering the period September 13-22, showed only a single impulsive outburst, which occurred at the very end of the 9 day pointing. The 3-25 A bremsstrahlung continuum displayed an overall decay during the 1.5 day Chandra observation on September 14-16, with a few superimposed mild enhancements. The VLA 3.5 cm and 20 cm radio light curves, obtained during a 10 hr period on September 15 immediately before the HST pointing, similarly revealed normal quiescent gyrosynchrotron emission and an absence of impulsive events. In contrast, the 7 hr STIS time series later on September 15 contained two distinct flares. The first was accompanied by intensification of the preexisting broad wings of the medium excitation species (e.g., Si IV λ1393 and C IV λ1548), while the second involved primarily the narrow cores of the lines, and even cooler temperatures. The Fe XXI λ1354 forbidden line showed little response to either flare, consistent with the contemporaneous soft X-ray and EUV light curves. The lack of coronal counterparts to the ultraviolet flares is unusual and suggests that they belong to a separate class of outbursts, sharing some similarities with the transition zone explosive events seen on the Sun. The density sensitive O IV λ1400 multiplet was not affected by either flare. The density sensitive Si III λ1300 multiplet showed little response to the first flare, but a dramatic brightening in the second, likely due to the lower peak temperature of that event. The O IV line ratios were near their low-density limits and suggest ne ~ 1010 cm-3 for the duration of the HST observations. The Si III ratios during the second flare rise indicate ne ~ 7 × 1010 cm-3. The far-UV diagnostics jointly imply electron pressures of neT ~ 2 × 1015 K cm-3, if formed close to their respective ionization equilibrium temperatures. The helium-like triplets of O VII, Ne IX, and Mg XI in the HETGS spectra have forbidden-to-intercombination line ratios consistent with average coronal electron densities of 1011 cm-3 at T ~ 0.3-1 × 107 K over the duration of the Chandra pointing. Fe XXI λ102/λ128 and λ142/λ128 ratios from EUVE suggest ne 1012-1013 cm-3, near 107 K. Thus, the coronal electron pressures could be as much as several orders of magnitude larger than those of the lower atmosphere. We constructed time-resolved spectra from the HETGS event lists and measured the centroids of the three brightest X-ray lines of HR 1099 in 60 minute bins. In high-S/N Ne X λ12.1, we believe that we can see the changing radial velocity of the K1 IV star over the half an orbital cycle recorded by Chandra. The amplitude of the velocity change is only ~100 km s-1 over the 1.5 day interval, a small fraction of the 300-500 km s-1 resolution of the HETGS at 12 A. Ne X λ12.1 also displayed a transient blueshift of ~60 km s-1 immediately prior to the first STIS flare, during which the far-UV lines briefly exhibited blueshifts of similar magnitude. The apparent displacement of Ne X appears independently in the -1 and +1 orders of the medium energy band (MEG), but there was no confirmation in the redundant high energy band (HEG), nor in other X-ray lines. Fe XXI λ1354 showed a blueshift about 30 minutes later at the beginning of the second HST orbit, but only at the 20 km s-1 level. Analogous HETGS time series of the brightest lines of comparison star Capella (α Aurigae; G8 III + G1 III) exhibited steady behavior, consistent with measurement uncertainties, without the transient Doppler bursts seen in HR 1099. Although the reality of the Ne X Lyα blueshift is in doubt, there is no question that the Chandra HETGS velocity scales are stable and free from large systematic errors.

Gas—Dust Shells around Some Early-Type Stars with an IR Excess (of Emission)

The results of an investigation of IR (IRAS) observations of 58 O—B—A—F stars of different luminosity classes, which are mainly members of various associations, are presented. The color indices of these stars are determined and two-color diagrams are constructed. The emission excesses at 12 and 25 mm (E12 and E25) are also compared with the absorption ΔA1640 of UV radiation. It is concluded that 24 stars (of the 58 investigated) are disk systems of the “Vega type,” to which Vega = N 53 also belongs. Eight known stars of the “Vega type” are also given in the figures for comparison. The remaining 34 stars may have gas—dust shells and/or shell—disks. The IR emission excesses of the 34 investigated stars and 11 comparison stars (eight of them are Be-Ae stars) are evidently due both to thermal emission from grains and to the emission from free—free transitions of electrons in the gas—dust shells of these stars.

VRI comparison stars for selected active galaxies

We present V (Johnson) and RI (Cousins) magnitudes of eld comparison stars for 12 bright Seyfert galaxies. These stars are closer than 6 0 (typically 3 0 4 0 ) to the galaxy and have V magnitudes between 10 m and 6 m . The sequences could be used for CCD monitor- ing and dierential photometry of these active galaxies, aimed to better understanding the physics of their vari- ability. Photometric errors of measured stars are in the range 0: m 03 0: 06. Finding charts (15 0 15 0 ) are also included.

Comparison Star Sequences for Optical Photometry of Active Galactic Nuclei and Quasars

As part of a campaign to monitor 23 quasars and Seyfert 1 galaxies on timescales of minutes to a few months, we obtained broadband relative photometry of more than 140 different stars. We attained typical 1 ? flux uncertainties of 2% through differential photometry of field stars in the same CCD frames as the active galactic nuclei (AGNs). These stars form i-band (?eff ~ 0.7 ?m), yellow (0.59 ?m), and blue (0.45 ?m) photometric sequences for the further monitoring of these AGNs. For about half these fields, we use absolute photometry to calibrate the relative magnitudes. Finding charts, filter prescriptions, comparison star relative photometry, and some tentative variable star identifications are presented. Also included are the foundations of the AGN photometry, which appears in a companion paper in The Astrophysical Journal.

Stellar Iron Abundances at the Galactic Center

We present measurements of (Fe/H) for six M supergiant stars and three giant stars within 2.5 pc of the Galactic center (GC) and one M supergiant star within 30 pc of the GC. The results are based on high-resolution (j/*j 40,000) K-band spectra, taken with CSHELL at the NASA Infrared Telescope Facility. We determine the iron abundance by detailed abundance analysis, performed with the spectral synthesis program MOOG. The mean (Fe/H) of the GC stars is determined to be near solar, (Fe/H) ) 0.12 ^ 0.22. Our analysis is a diUerential analysis, as we have observed and applied the same analysis technique to 11 cool, luminous stars in the solar neighborhood with similar temperatures and luminosities as the GC stars. The mean (Fe/H) of the solar neighborhood comparison stars, (Fe/H) \) 0.03 ^ 0.16, is similar to that of the GC stars. The width of the GC (Fe/H) distribution is found to be narrower than the width of the (Fe/H) distribution of Baades window in the bulge but consistent with the width of the (Fe/H) distribution of giant and supergiant stars in the solar neighbor- hood. Subject headings: Galaxy: abundancesGalaxy: centerGalaxy: stellar content ¨ stars: abundancesstars: late-type

NICMOS Imaging of the Damped Lyα Absorber atz = 1.89 toward LBQS 1210+1731: Constraints on Size and Star Formation Rate

We report results of a high-resolution imaging search for the galaxy associated with the damped Lyα (DLA) absorber at z = 1.892 toward the z_(em) = 2.543 quasar LBQS 1210+1731, using the Hubble Space Telescope (HST) NICMOS. The images were obtained in the broad filter F160W and the narrow filter F190N with camera 2 on NICMOS and were aimed at detecting the absorber in the rest-frame optical continuum and in Hα line emission from the DLA absorber. After suitable point-spread function (PSF) subtractions, a feature is seen in both the broadband and narrowband images, at a projected separation of 0.25 from the quasar. This feature may be associated with the DLA absorber, although we cannot completely rule out that it could be a PSF artifact. If associated with the DLA, the object would be ≈ 2-3 h^(-)_(07) kpc in size with a flux of 9.8 ± 2.4 μJy in the F160W filter, implying a luminosity at λ_(central) = 5500 A in the rest frame of 1.5 × 10^(10) h^(-2)_(70) L_☉ at z = 1.89, for q_0 = 0.5. However, a comparison of the fluxes in the broad and narrow filters indicates that most of the flux in the narrowband filter is continuum emission, rather than redshifted Hα line emission. This suggests that if this object is the absorber, then either it has a low star formation rate (SFR), with a 3 σ upper limit of 4.0 h^(-2)_(70) M_☉ yr^(-1), or dust obscuration is important. It is possible that the Hα emission may be extinguished by dust, but this seems unlikely, given the typically low dust-to-gas ratios observed in DLAs. Alternatively, the object, if real, may be associated with the host galaxy of the quasar rather than with the damped Lyα absorber. H-band images obtained with the NICMOS camera 2 coronagraph show a much fainter structure ≈4-5 h^(-2)_(70) kpc in size and containing four knots of continuum emission, located 0.7 away from the quasar. This structure is not seen in images of comparison stars after similar PSF subtractions and is also likely to be associated with the absorbing galaxy or its companions, although we do not know its redshift. We have probed regions far closer to the quasar sight line than in most previous studies of high-redshift intervening DLAs. The two objects we report mark the closest detected high-redshift DLA candidates yet to any quasar sight line. If the features in our images are associated with the DLA, they suggest faint, compact, somewhat clumpy objects rather than large, well-formed protogalactic disks or spheroids. If the features are PSF artifacts, then the constraints on sizes and star formation rates of the DLA are even more severe. The size, luminosity, and SFR estimates mentioned above should therefore be conservatively considered as upper limits.

Variable Stars in M13. I. Positions and [ITAL]UBVRI[/ITAL] Photometry for Variables, Suspected Variables, and Comparison Stars

Photoelectric and photographic UBVRI photometry is presented for 104 of the brighter stars in the field of the globular cluster M13 (NGC 6205). The observed objects include the known variable stars of the cluster, suspected variables, and a number of field stars suitable for calibrating CCD and photographic images and for serving as comparison stars for studies of the variables. Accurate relative J2000.0 positions for the stars are also given.

A deep echelle survey and new analysis of diffuse interstellar bands

We report a deep survey of diffuse interstellar bands (DIBs) between 3906 A and 6812 Aunder consistent observing conditions toward three very reddened and five unreddened stars. BD+63° 1964's line-of-sight was shown to present exceptional DIB enhancement in number as well as in strength. The early spectral type of the star and the use of spectra of an unreddened comparison star of the same spectral type allowed to limit stellar line residuals. Using careful reduction and analysis methods we discovered 60 new DIBs which are confirmed in the reddened targets HD 183143 and BD+40° 4220. We detected 25 possible DIBs which still await further confirmation, but we did not detect or confirm 28 previously reported DIBs. The present survey with 226 confirmed DIBs, measured in three targets allows a detailed and homogeneous statistical analysis on the distribution of DIB widths and intensities.

Photometric and CaiiH and K Spectroscopic Variations in Nearby Sun‐like Stars with Planets. III.

We present the results of an analysis of time-series photometry, Ca II H and K spectrophotometry, and high-dispersion visible spectra of nine nearby Sun-like stars recently identified as having planets. For the six stars whose presumed planets have orbital periods of less than 4 months (? Boo, 51 Peg, ? And, ?1 Cnc, ? CrB, and 70 Vir), sine-curve fits to the photometric data show no variations with semiamplitude greater than 1 or 2 parts in 104. Photometric variations in 47 UMa are similarly small, although our photometric data of this star are slightly affected by variability of the comparison star. Nonvariability at this level of precision is sufficient to rule out surface magnetic activity as the cause of the observed radial-velocity variations in these seven stars and makes nonradial pulsations unlikely as well. Thus, our photometry provides indirect but strong support for true reflex motions?planets?in these seven stars, but cannot yet so support the planetary hypothesis for the two additional stars, 16 Cyg B and Gl 411. Continued photometric monitoring of the short-period systems may soon result in the direct detection of these planets in reflected light. We have used our photometric fluxes to search for possible transits of the extrasolar planets. Transits definitely do not occur in ? Boo, 51 Peg, ? And, and ?1 Cnc, and probably do not occur in ? CrB and 70 Vir. Our transit-search results are inconclusive for 47 UMa, and we cannot address the issue for 16 Cyg B and Gl 411. The precision of our photometry is sufficient to detect transits of planets even if they are not gas giants, as currently assumed, but much smaller objects with rocky compositions. The chance of finding at least one transit in the six stars is ~40%. We find significant year-to-year photometric variability only in ? Boo, which is not only the youngest star in the sample but also the star with the shallowest convective zone. The interseasonal range in its yearly mean photometric flux is ~0.002 mag, roughly twice the 0.0008 mag decadal variation in the Sun's total irradiance. Monitoring of the relative Ca II H and K fluxes began between 1966 and 1968 for 51 Peg, ? Boo, ? CrB, and Gl 411, between 1990 and 1993 for 47 UMa, 70 Vir, 16 Cyg B, and ?1 Cnc, and in 1996 for ? And. The data have been newly recalibrated for improved long-term instrumental stability, resulting in better precision of the Ca II records. Five of the nine stars in this study have little or no detectable year-to-year variation in Ca II flux. The remaining four show moderate or pronounced variability: ? Boo, whose radial-velocity and photometric variations have comparatively high amplitudes; Gl 411, whose planetary companion was inferred astrometrically, not spectroscopically; ?1 Cnc, which may undergo decadal cyclic activity; and ? And, which shows moderate year-to-year variability. Except for 47 UMa, intraseasonal variability consistent with rotation was detected in the Ca II records of all stars. However, the rotation periods determined for ? And, 70 Vir, and 16 Cyg B are of low confidence. An examination of the recalibrated Ca II records for 51 Peg finds a rotation period of 22 days, in contrast to our previous result of 37 days. Ages have been estimated from the mean Ca II flux and, where possible, the rotation period. We find general consistency with the ages determined by others comparing properties determined from high-resolution spectroscopy to evolutionary models, although the uncertainties are, in general, large.

The carbon Cepheid RT Trianguli Australis: additional evidence of triple- and CNO cycling

We have used echelle spectra of resolving power 35 000 to derive chemical abundances and the 12C/13C ratio in the 1.9-d carbon Cepheid RT TrA and the Cepheid U TrA, employed as a comparison star. We confirm that RT TrA is very metal-rich with [Fe/H]=+0.4. In addition, C and N are substantially in excess, and a small deficiency in O is present. We interpret these anomalies as resulting from the appearance on the stellar surface of material enriched in 12C by the 3-α process, followed by CNO cycling to convert 12C to 13C and 14N. In addition, some 16O has been processed to 14N. The partial processing of 16O to 14N indicates that substantial 17O may be present. Proton capture seems to have enhanced 23Na from the Ne isotopes.

Observational Proof of the ZZ Ceti Red Edge

With a time-series CCD photometry survey, we have demonstrated clearly that the observed red edge for the ZZ Ceti stars instability strip at 11,000 K is not an observational selection effect. Previous surveys for variability among hydrogen atmosphere white dwarfs at around 11,000 K have been carried out using high speed photometry which suffers from variable extinction effects that start becoming important at periods of 15 minutes. In our survey we constantly monitor the sky brightness as well as one or more comparison stars. This is done through the same color filter, therefore minimizing adverse effects of differential extinction. The fact that the theoretical red edge should be around 8,000 K remains, but effects not included in the theory, especially convection-aulsation interaction, could explain it.

Photometric confirmation of the δ Scuti pulsational variability in the pre-main-sequence Herbig Ae star HD 104237

Photometric observations of the Herbig Ae star HD104237 confirm that it is a d Scuti star. We find two periods, the highest amplitude one having a value of 43min. This is only the fourth known pre-main-sequence d Scuti star, and the only one with such short periods. These imply high-overtone modes which have not yet been investigated theoretically. Two of our comparison stars, HD104036 and 105234, are newly discovered d Scuti stars.

Spectral and luminosity classification for the cool components in symbiotic stars

The near infrared spectra of 12 S-type symbiotic stars and 78 comparison stars have been observed with moderate dispersion in five runs from 1992 to 1997, the resolving power being R = lambda/Delta lambda > 2000, with a signal to noise ratio SIN > 100. The triple-headed absorption band of TiO (lambda lambda 8432, 8422 and 8452 Angstrom) emerges when a star is later than M2, and the depth of the TiO absorption band is very sensitive to the spectral type (ST) and insensitive to the luminosity class of the star. We fit a curve of spectral type against the index of the absorption depth of this band with a standard deviation sigma = 0.37 of a subdivision of one spectral type. The IR all triplet (lambda lambda 8498, 8542, 8662 Angstrom); Fe I 8689 Angstrom: and Fe I 8675 Angstrom are good luminosity indicators although the equivalent widths (EWs) of these lines clearly decrease fora star later than M3. When the star is a supergiant the lines have a smaller central residual intensity and broader wings than in the case of a normal giant. The Ca II 8662 Angstrom/Fe I 8675 Pi and Fe I 8689 Angstrom/Fe I 8675 A ratios are also good luminosity indicators for Ii-type giants. The latter is particularly useful when there are abundance anomalies. The metal-poor symbiotic star AG Dra is classified as a Ib or II giant, as is TX CVn, on the basis of Fe I 8689 Angstrom/Fe I 8675 Angstrom. 9 other symbiotic stars containing M-type cool components are classified as giants by direct comparison and quantitative analysis. Due to there being no known good ratio indicator of luminosity for M-type stars in the band studied and because there is no metal abundance data for the symbiotic stars studied by us except for AG Dra, the results for these 9 symbiotic stars are only preliminary. The infrared Ca II triplet of most symbiotic stars clearly varies between the different observing runs. The different luminosity classes given to the same symbiotic star are probably caused by the variability of the lines of ionized elements,: while in some cases they are affected by a low metal abundance.

CH, CN, and NH Band Strengths of Metal‐poor Cluster and Field Red Giants

ABSTRACTThe strengths of the CN, NH, and CH bands in the spectra of Population II red giants are discussed based on observations of a sample of both globular cluster and field giants. We confirm an anticorrelation between the oxygen abundance and the CN indices and a correlation between the 3883 Å CN band and the 3360 Å NH band strengths among giants in the globular clusters M15 and M13. We find one M15 star (IV‐38) with a strong 3883 Å CN band and detectable 4215 Å CN and 3360 Å NH bands. Abundance analysis of M15 IV‐38 reveals a comparable carbon abundance to a comparison star that has much weaker CN bands. One possible reason for this may be that IV‐38 is an insipid CH star that has also undergone some deep mixing. Alternatively, the atmosphere of IV‐38 may have been extensively processed through the O→N cycle of hydrogen burning such that carbon has been affected by O→C conversion. By combining our data set with material from the literature and high‐quality B−V photometry, we find that the CN band strength differences among the M5 red giants do not appear to broaden the giant branch of that cluster within the photometric errors. Using the CN, CH, and NH bands, we are able to confirm that the metal‐poor field giant HD 135148 is a CH‐strong star and has not undergone deep mixing.

Techniques for Automated High‐Precision Photometry of Sun‐like Stars

ABSTRACTTennessee State University operates several Automatic Photoelectric Telescopes (APTs) located at Fairborn Observatory in the Patagonia Mountains of southern Arizona. The APTs are dedicated to photometric monitoring programs that would be difficult and expensive to accomplish without the advantages provided by automation. I describe the operation of two of the telescopes (0.75 and 0.80 m APTs) and the quality‐control techniques that result in their routine acquisition of single‐star differential photometry with a precision of 0.001 mag for single observations and 0.0001–0.0002 mag for seasonal means. I show that a primary obstacle to photometry at this level of precision is intrinsic variability in the comparison stars. Finally, I illustrate the capabilities of the APTs with sample results from a program to measure luminosity cycles in Sun‐like stars and a related effort to search for extrasolar planets around these stars.

A Reanalysis of the Ultraviolet Extinction from Interstellar Dust in the Large Magellanic Cloud

We have reanalyzed the Large Magellanic Cloud's (LMC) ultraviolet (UV) extinction using data from the IUE final archive. Our new analysis takes advantage of the improved signal-to-noise ratio of the IUE NEWSIPS reduction, the exclusion of stars with very low reddening, the careful selection of well-matched comparison stars, and an analysis of the effects of Galactic foreground dust. Differences between the average extinction curves of the 30 Dor region and the rest of the LMC are reduced compared with previous studies. We find that there is a group of stars with very weak 2175 A bumps that lie in or near the region occupied by the supergiant shell, LMC 2, on the southeast side of 30 Dor. The average extinction curves inside and outside LMC 2 show a very significant difference in 2175 A bump strength, but their far-UV extinctions are similar. While it is unclear whether or not the extinction outside the LMC 2 region can be fitted with the relation of Cardelli, Clayton, & Mathis (CCM), sight lines near LMC 2 cannot be fitted with CCM because of their weak 2175 A bumps. While the extinction properties seen in the LMC lie within the range of properties seen in the Galaxy, the correlations of UV extinction properties with environment seen in the Galaxy do not appear to hold in the LMC.

Spectral classification of the cool components of symbiotic stars

We have made near infrared spectroscopic observations of 10 symbiotic and 27 K-M comparison stars. For stars later than M3, we found the band depth of the triple-headed TiO absorption band to be sensitive to temperature and insensitive to gravity. We fitted the spectral type to the band depth with a standard error of 0.22 of a subtype and derived the spectral types for 6 symbiotic stars. We measured the EW of a large number of lines including the CaII lines (very sensitive to luminosity), the FeI and TiO lines (moderately sensitive) and the NaI lines (not sensitive). The EW of these lines vary with the spectral type, particularly for stars later than M3, both spectral type and luminosity effects must be considered. We give the luminosity classes for 10 of the brighter symbiotic stars, they are all giant stars, showing no features of bright giants or supergiants.