The Galactic Kinematics of Mira Variables

The galactic kinematics of Mira variables derived from radial velocities, Hipparcos proper motions and an infrared period-luminosity relation are reviewed. Local Miras in the 145-200day period range show a large asymmetric drift and a high net outward motion in the Galaxy. Interpretations of this phenomenon are considered and (following Feast and Whitelock 2000) it is suggested that they are outlying members of the bulge-bar population and indicate that this bar extends beyond the solar circle.Comment: 7 pages, 2 figure, to be published in Mass-Losing Pulsating Stars and their Circumstellar Matter, Y. Nakada & M. Honma (eds) Kluwer ASSL serie

Imaging the Radio Photospheres of Mira Variables

We have used the VLA at 43 GHz to image the radio continuum emission from o Ceti, R Leo, and W Hya and to precisely locate their SiO maser emission with respect to the star. The radio continuum emission region for all three stars has a diameter close to 5.6 AU. These diameters are similar to those measured at infrared wavelengths in bands containing strong molecular opacity and about twice those measured in line-free regions of the infrared spectrum. Thus, the radio photosphere and the infrared molecular layer appear to be coextensive. The 43 GHz continuum emission is consistent with temperatures near 1600 K and opacity from H-minus free-free interactions. While the continuum image of o Ceti appears nearly circular, both R Leo and W Hya display significant elongations. The SiO masers for all three stars show partial rings with diameters close to 8 AU.Comment: 14 pages; 3 figure

Hipparcos period-luminosity relations for Miras and semiregular variables

We present period-luminosity diagrams for nearby Miras and semiregulars, selecting stars with parallaxes better than 20 per cent and well-determined periods. Using K-band magnitudes, we find two well-defined P-L sequences, one corresponding to the standard Mira P-L relation and the second shifted to shorter periods by a factor of about 1.9. The second sequence only contains semiregular variables, while the Mira sequence contains both Miras and semiregulars. Several semiregular stars show double periods in agreement with both relations. The Whitelock evolutionary track is shown to fit the data, indicating that the semiregulars are Mira progenitors. The transition between the two sequences may correspond to a change in pulsation mode or to a change in the stellar structure. Large amplitude pulsations leading to classical Mira classification occur mainly near the tip of the local AGB luminosity function.Comment: 10 pages with figures, accepted by ApJ Letter

Long Period Variables in Globular Clusters and the Galactic Bulge: Their Dependence on Metallicity

We derive the frequency of occurrence of luminous long period variables (LLPVs) in globular clusters and in the Baade's Window field of the Galactic bulge. LLPVs occur only in clusters with [Fe/H]>/= -1.0. In these clusters their frequency of occurrence relative to the number of giant stars appears to be independent of metallicity. Integrated over all metallicities, Baade's Window appears to be deficient in LLPVs. We estimate [Fe/H] values for Baade's Window LLPVs from their period and a log P vs. [Fe/H] relation derived from cluster variables and find that LLPVs with [Fe/H]>/= 0.0 are absent from Baade's Window. We propose that this is because of enhanced mass loss rates in these LLPVs with a consequently abbreviated lifetime compared to lower metallicity LLPVs. A typical lifetime for cluster LLPVs is about 3 x10^5 yrs. Finally, we call attention to the need for a much more complete survey for LLPVs in globular clusters.Comment: 20 pages of text plus tables in PS format created by MS WORD97; 9 figures in PS format generated by SigmaPlot; all in one gzipped tar file; originally submitted to ApJ but has now been accepted and is in press at the AJ with minor revisions and some amplifications from previous versio

The Distances of SNR W41 and overlapping HII regions

New HI images from the VLA Galactic Plane Survey show prominent absorption features associated with the supernovae remnant G23.3-0.3 (SNR W41). We highlight the HI absorption spectra and the $^{13}$CO emission spectra of eight small regions on the face of W41, including four HII regions, three non-thermal emission regions and one unclassified region. The maximum velocity of absorption for W41 is 78$\pm$2 km/s and the CO cloud at radial velocity 95$\pm$5 km/s is behind W41. Because an extended TeV source, a diffuse X-ray enhancement and a large molecular cloud at radial velocity 77$\pm$5 km/s are also projected at the center of W41, these yield the kinematic distance of 3.9 to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21 and G23.07+0.25 are at the far kinematic distances ($\sim$9.9 kpc and $\sim$ 10.6 kpc respectively) of their recombination-line velocities (103$\pm$0.5 km/s and 89.6$\pm$2.1 km/s respectively), G23.07-0.37 is at the near kinematic distance (4.4$\pm$0.3 kpc) of its recombination-line velocity (82.7$\pm$2.0 km/s), and G23.27-0.27 is probably at the near kinematic distance (4.1$\pm$0.3 kpc) of its recombination-line velocity (76.1$\pm$0.6 km/s).Comment: 11 pages, 3 figs., 2 tables, accepted by A

Radio Emission Associated with Ultraluminous X-ray Sources in the Galaxy Merger NGC 3256

We present new 6, 3.6, and 2 cm VLA radio observations of the nearby merger system NGC 3256, with resolutions of ~100 pc, which reveal compact radio sources embedded in more diffuse emission at all three wavelengths. The two radio nuclei are partially resolved, but the two dominant compact sources that remain coincide with the two most powerful compact Ultraluminous X-ray sources (ULXs) recently reported by Lira et al. The radio/X-ray ratios for these two sources are too high by factors of >100-1000 to be normal X-ray binaries. However, their radio and X-ray powers and ratios are consistent with low-luminosity active galactic nuclei (LLAGNs), and optical emission lines suggest the presence of a nuclear disk around the northern nucleus. If the two nuclear ULXs are LLAGNs, their associated black holes are separated by only \~1kpc, about 6 times closer to one another than those found recently in the merger galaxy NGC 6240. A third ULX on the outskirts of the merger is also a radio source, and probably is a collection of supernova remnants. The remaining ULXs are not coincident with any source of compact radio emission, and are consistent with expectations for beamed X-ray binaries or intermediate-mass black holes.Comment: Accepted for ApJ (10 pages, 5 figures

A New Kinematic Distance Estimator to the LMC

The distance to the Large Magellanic Cloud (LMC) can be directly determined by measuring three of its properties, its radial-velocity field, its mean proper motion, and the position angle \phi_ph of its photometric line of nodes. Statistical errors of 2% are feasible based on proper motions obtained with any of several proposed astrometry satellites, the first possibility being the Full-Sky Astrometric Mapping Explorer (FAME). The largest source of systematic error is likely to be in the determination of \phi_ph. I suggest two independent methods to measure \phi_ph, one based on counts of clump giants and the other on photometry of clump giants. I briefly discuss a variety of methods to test for other sources of systematic errors.Comment: submitted to ApJ, 13 page

The Distance to the M31 Globular Cluster System

The distance to the centroid of the M31 globular cluster system is determined by fitting theoretical isochrones to the observed red-giant branches of fourteen globular clusters in M31. The mean true distance modulus of the M31 globular clusters is found to be 24.47 +/- 0.07 mag. This is consistent with distance modulii for M31 that have been obtained using other distance indicators.Comment: 11 pages, 2 postscript figures, uses aaspp4.sty, to be published in the May 1998 Astronomical Journa

An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-Through-UV Curve Morphology

We study the IR-through-UV interstellar extinction curves towards 328 Galactic B and late-O stars. We use a new technique which employs stellar atmosphere models in lieu of unreddened "standard" stars. This technique is capable of virtually eliminating spectral mismatch errors in the curves. It also allows a quantitative assessment of the errors and enables a rigorous testing of the significance of relationships between various curve parameters, regardless of whether their uncertainties are correlated. Analysis of the curves gives the following results: (1) In accord with our previous findings, the central position of the 2175 A extinction bump is mildly variable, its width is highly variable, and the two variations are unrelated. (2) Strong correlations are found among some extinction properties within the UV region, and within the IR region. (3) With the exception of a few curves with extreme (i.e., large) values of R(V), the UV and IR portions of Galactic extinction curves are not correlated with each other. (4) The large sightline-to-sightline variation seen in our sample implies that any average Galactic extinction curve will always reflect the biases of its parent sample. (5) The use of an average curve to deredden a spectral energy distribution (SED) will result in significant errors, and a realistic error budget for the dereddened SED must include the observed variance of Galactic curves. While the observed large sightline-to-sightline variations, and the lack of correlation among the various features of the curves, make it difficult to meaningfully characterize average extinction properties, they demonstrate that extinction curves respond sensitively to local conditions. Thus, each curve contains potentially unique information about the grains along its sightline.Comment: To appear in the Astrophysical Journal, Part 1, July 1, 2007. Figures and Tables which will appear only in the electronic version of the Journal can be obtained via anonymous ftp from ftp://ftp.astronomy.villanova.edu . After logging in, change directories to "fitz/FMV_EXTINCTION". A README file describes the various files present in the director