Variable Stars in the Globular Cluster M5. Application of the Image Subtraction Method

We present $V$-band light curves of 61 variables from the core of the globular cluster M5 obtained using a newly developed image subtraction method (ISM). Four of these variables were previously unknown. Only 26 variables were found in the same field using photometry obtained with DoPHOT software. Fourier parameters of the ISM light curves have relative errors up to 20 times smaller than parameters measured from DoPHOT photometry. We conclude that the new method is very promising for searching for variable stars in the cores of the globular clusters and gives very accurate relative photometry with quality comparable to photometry obtained by HST. We also show that the variable V104 is not an eclipsing star as has been suggested, but is an RRc star showing non-radial pulsations.Comment: submitted to MNRAS, 9 pages, 4 figure

Microlensing of Circumstellar Disks

We investigate the microlensing effects on a source star surrounded by a circumstellar disk, as a function of wavelength. The microlensing light curve of the system encodes the geometry and surface brightness profile of the disk. In the mid- and far-infrared, the emission of the system is dominated by the thermal emission from the cold dusty disk. For a system located at the Galactic center, we find typical magnifications to be of order 10-20% or higher, depending on the disk surface brightness profile, and the event lasts over one year. At around 20 microns, where the emission for the star and the disk are comparable, the difference in the emission areas results in a chromatic microlensing event. Finally, in the near-infrared and visible, where the emission of the star dominates, the fraction of star light directly reflected by the disk slightly modifies the light curve of the system which is no longer that of a point source. In each case, the corresponding light curve can be used to probe some of the disk properties. A fraction of 0.1% to 1% optical microlensing events are expected to be associated with circumstellar disk systems. We show that the lensing signal of the disk can be detected with sparse follow-up observations of the next generation space telescopes. While direct imaging studies of circumstellar disks are limited to the solar neighborhood, this microlensing technique can probe very distant disk systems living in various environments and has the potential to reveal a larger diversity of circumstellar disks.Comment: 9 pages, 7 figures. Accepted for publication in Ap

Limits on I-band microvariability of the Galactic Bulge Miras

We search for microvariability in a sample of 485 Mira variables with high quality I-band light curves from the second generation Optical Gravitational Lensing Experiment (OGLE-II). Rapid variations with amplitudes in the ~0.2-1.1 mag range lasting hours to days were discovered in Hipparcos data by de Laverny et al. (1998). Our search is primarily sensitive to events with time-scales of about 1 day, but retains a few percent efficiency (per object) for detecting unresolved microvariability events as short as 2 hours. We do not detect any candidate events. Assuming that the distribution of the event time profiles is identical to that from the Hipparcos light curves we derive the 95% confidence level upper limit of 0.038 per year per star for the rate of such events (1 per 26 years per average object of the ensemble). The high event rates of the order of 1 per year per star implied by the Hipparcos study in the H_P band are excluded with high confidence by the OGLE-II data in the I band. Our non-detection could still be explained by much redder spectral response of the I filter compared to the H_P band or by population differences between the bulge and the solar neighborhood. In any case, the OGLE-II I-band data provide the first limit on the rate of the postulated microvariability events in Mira stars and offer new quantitative constraints on their properties. Similar limits are obtained for other pulse shapes and a range of the assumed time-scales and size-frequency distributions.Comment: Accepted for publication in Ap

The Major Heat Shock Proteins, Hsp70 and Hsp90, in 2-Methoxyestradiol-Mediated Osteosarcoma Cell Death Model

2-Methoxyestradiol is one of the natural 17β-estradiol derivatives and a potential novel anticancer agent currently being under evaluation in advanced phases of clinical trials. However, the mechanism of anticancer action of 2-methoxyestradiol has not been yet fully established. In our previous studies we have demonstrated that 2-methoxyestradiol selectively induces the expression and nuclear translocation of neuronal nitric oxide synthase in osteosarcoma 143B cells. Heat shock proteins (Hsps) are factors involved in the regulation of expression and activity of nitric oxide synthases. Herein, we chose osteosarcoma cell lines differed in metastatic potential, metastatic 143B and highly metastatic MG63.2 cells, in order to further investigate the anticancer mechanism of 2-methoxyestradiol. The current study aimed to determine the role of major heat shock proteins, Hsp90 and Hsp70 in 2-methoxyestradiol-induced osteosarcoma cell death. We focused on the implication of Hsp90 and Hsp70 in control under expression of neuronal nitric oxide synthase, localization of the enzyme, and further generation of nitro-oxidative stress. To give the insight into the role of Hsp90 in regulation of anticancer efficacy of 2-methoxyestradiol, we used geldanamycin as a potent Hsp90 inhibitor. Herein, we evidenced that inhibition of Hsp90 controls the protein expression of 2-methoxyestradiol-induced neuronal nitric oxide synthase and inhibits enzyme nuclear translocation. We propose that decreased level of neuronal nitric oxide synthase protein after a combined treatment with 2-methoxyestradiol and geldanamycin is directly associated with the accompanying upregulation of Hsp70 and downregulation of Hsp90. This interaction resulted in abrogation of anticancer efficacy of 2-methoxyestradiol by geldanamycin

Molecular Gas in Candidate Double Barred Galaxies III. A Lack of Molecular Gas?

Most models of double-barred galaxies suggest that a molecular gas component is crucial for maintaining long-lived nuclear bars. We have undertaken a CO survey in an attempt to determine the gas content of these systems and to locate double barred galaxies with strong CO emission that could be candidates for high resolution mapping. We observed 10 galaxies in CO J=2-1 and J=3-2 and did not detect any galaxies that had not already been detected in previous CO surveys. We preferentially detect emission from galaxies containing some form of nuclear activity. Simulations of these galaxies require that they contain 2% to 10% gas by mass in order to maintain long-lived nuclear bars. The fluxes for the galaxies for which we have detections suggest that the gas mass fraction is in agreement with these models requirements. The lack of emission in the other galaxies suggests that they contain as little as 7 x 10^6 solar masses of molecular material which corresponds to < 0.1% gas by mass. This result combined with the wide variety of CO distributions observed in double barred galaxies suggests the need for models of double-barred galaxies that do not require a large, well ordered molecular gas component.Comment: 17 pages (3 figures embedded on pg 17). To appear in the March 10 issue of the Astrophysical Journa

Stellar kinematics for the central spheroid in the Polar Disk Galaxy NGC4650A

We have obtained high angular resolution, high signal-to-noise spectra of the Calcium triplet absorption lines on the photometric axes of the stellar spheroid in the polar disk galaxy NGC4650A. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically decoupled nucleus, and a flat velocity dispersion profile. The minor axis kinematics is determined for the first time: along this direction some rotation is measured, and the velocity dispersion is nearly constant and slightly increases at larger distances from the center. The new high resolution kinematic data suggest that the stellar component in NGC4650A resembles a nearly-exponential oblate spheroid supported by rotation. The main implications of these results on the previous mass models for NGC4650A are discussed. Moreover, the new kinematic data set constraints on current models for the formation scenarios of Polar Ring Galaxies (PRGs), supporting a slow accretion rather then a secondary strong dissipative event.Comment: 25 pages, 8 figures, accepted for publication in the Astrophysical Journa

Z-dependent Barriers in Multifragmentation from Poissonian Reducibility and Thermal Scaling

We explore the natural limit of binomial reducibility in nuclear multifragmentation by constructing excitation functions for intermediate mass fragments (IMF) of a given element Z. The resulting multiplicity distributions for each window of transverse energy are Poissonian. Thermal scaling is observed in the linear Arrhenius plots made from the average multiplicity of each element. ``Emission barriers'' are extracted from the slopes of the Arrhenius plots and their possible origin is discussed.Comment: 15 pages including 4 .ps figures. Submitted to Phys. Rev. Letters. Also available at http://csa5.lbl.gov/moretto