M Dwarfs from Hubble Space Telescope Star Counts. IV

We study a sample of about 1400 disk M dwarfs that are found in 148 fields observed with the Wide Field Camera 2 (WFC2) on the Hubble Space Telescope and 162 fields observed with pre-repair Planetary Camera 1 (PC1), of which 95 of the WFC2 fields are newly analyzed. The method of maximum likelihood is applied to derive the luminosity function and the Galactic disk parameters. At first, we use a local color-magnitude relation and a locally determined mass-luminosity relation in our analysis. The results are consistent with those of previous work but with considerably reduced statistical errors. These small statistical errors motivate us to investigate the systematic uncertainties. Considering the metallicity gradient above the Galactic plane, we introduce a modified color-magnitude relation that is a function of Galactic height. The resultant M dwarf luminosity function has a shape similar to that derived using the local color-magnitude relation but with a higher peak value. The peak occurs at $M_V \sim 12$ and the luminosity function drops sharply toward $M_V \sim 14$. We then apply a height-dependent mass-luminosity function interpolated from theoretical models with different metallicities to calculate the mass function. Unlike the mass function obtained using local relations, which has a power-law index $\alpha = 0.47$, the one derived from the height-dependent relations tends to be flat ($\alpha = -0.10$). The resultant local surface density of disk M dwarfs (12.2 +/- 1.6 M_sun pc^{-2}) is somewhat smaller than the one obtained using local relations (14.3 +/- 1.3 M_sun pc^{-2}). Our measurement favors a short disk scale length, H = 2.75 +/- 0.16 (statistical) +/- 0.25 (systematic) kpc.Comment: 20 pages, 10 ps figures, accepted for publication in Ap

Supernova 1996L: evidence of a strong wind episode before the explosion

Observations of the type II SN 1996L reveal the presence of a slowly expanding (V~700$ km/s) shell at ~ 10^(16) cm from the exploding star. Narrow emission features are visible in the early spectra superposed on the normal SN spectrum. Within about two months these features develop narrow symmetric P-Cygni profiles. About 100 days after the explosion the light curve suddenly flattens, the spectral lines broaden and the Halpha flux becomes larger than what is expected from a purely radioactive model. These events are interpreted as signatures of the onset of the interaction between the fast moving ejecta and a slowly moving outer shell of matter ejected before the SN explosion. At about 300 days the narrow lines disappear and the flux drops until the SN fades away, suggesting that the interaction phase is over and that the shell has been swept away. Simple calculations show that the superwind episode started 9 yr before the SN explosion and lasted 6 yr, with an average dM/dt=10^(-3) M_solar/yr. Even at very late epochs (up to day 335) the typical forbidden lines of [OI], CaII], [FeII] remain undetected or very weak. Spectra after day 270 show relatively strong emission lines of HeI. These lines are narrower than other emission lines coming from the SN ejecta, but broader than those from the CSM. These high excitation lines are probably the result of non-thermal excitation and ionization caused by the deposition of the gamma-rays emitted in the decay of radioactive material mixed in the He layer.Comment: 8 pages, 6 figures, Latex, To appear in M.N.R.A.

The Velocity Function of Galaxies

We present a galaxy circular velocity function, Psi(log v), derived from existing luminosity functions and luminosity-velocity relations. Such a velocity function is desirable for several reasons. First, it enables an objective comparison of luminosity functions obtained in different bands and for different galaxy morphologies, with a statistical correction for dust extinction. In addition, the velocity function simplifies comparison of observations with predictions from high-resolution cosmological N-body simulations. We derive velocity functions from five different data sets and find rough agreement among them, but about a factor of 2 variation in amplitude. These velocity functions are then compared with N-body simulations of a LCDM model (corrected for baryonic infall) in order to demonstrate both the utility and current limitations of this approach. The number density of dark matter halos and the slope of the velocity function near v_*, the circular velocity corresponding to an ~L_* spiral galaxy, are found to be comparable to that of observed galaxies. The primary sources of uncertainty in construction of Psi(log v) from observations and N-body simulations are discussed and explanations are suggected to account for these discrepancies.Comment: Latex. 28 pages, 4 figures. Accepted by Ap

Observation of Collective Excitations of the Dilute 2D Electron System

We report inelastic light scattering measurements of dispersive spin and charge density excitations in dilute 2D electron systems reaching densities less than 10^{10} cm^{-2}. In the quantum Hall state at nu=2, roton critical points in the spin inter--Landau level mode show a pronounced softening as r_s is increased. Instead of a soft mode instability predicted by Hartree--Fock calculations for r_s ~ 3.3, we find evidence of multiple rotons in the dispersion of the softening spin excitations. Extrapolation of the data indicates the possibility of an instability for r_s >~ 11.Comment: Submitted to Physical Review Letter

The rotation curve and mass-distribution in highly flattened galaxies

A new method is developed which permits the reconstruction of the surface-density distribution in the galactic disk of finite radius from an arbitrary smooth distribution of the angular velocity via two simple quadratures. The existence of upper limits for disk's mass and radius during the analytic continuation of rotation curves into the hidden (non-radiating) part of the disk is demonstrated.Comment: 13 pages, 2 figure

BVRI Surface Photometry of (S+S) Binary Galaxies. I. The data

We present multicolour broad band ($BVRI$) photometry for a sample of 33 spiral-spiral (S+S) binary galaxies drawn from the Karachentsev Catalogue of Isolated Pairs of Galaxies (KPG). The data is part of a joint observational programme devoted to systematic photometric study of one of the most complete and homogeneous pair samples available in the literature. We present azimuthally averaged colour and surface brightness profiles, colour index (B-I) maps, B band and sharp/filtered B band images as well as integrated magnitudes, magnitudes at different circular apertures and integrated colours for each pair. Internal and external data comparisons show consistency within the estimated errors. Two thirds of the sample have total aperture parameters homogeneously derived for the first time. After reevaluating morphology for all the pairs, we find a change in Hubble type for 24 galaxies compared to the original POSS classifications. More than half of our pairs show morphological concordance which could explain, in part, the strong correlation in the (B-V) colour indices (Holmberg Effect) between pair components. We find a tendency for barred galaxies to show grand design morphologies and flat colour profiles. The measurements will be used in a series of forthcoming papers where we try to identify and isolate the main structural and photometric properties of disk galaxies at different stages of interaction.Comment: 23 pages. 5 Figures. Accepted for publication in Astronomy and Astrophysics. Mosaics for all pairs can be found at http://www.inaoep.mx/~puerari/binar

Basal cutaneous pain threshold in headache patients

The aim of this study was to analyze cutaneous pain threshold (CPT) during the interictal phase in headache patients, and the relationships between headache frequency and analgesic use. A consecutive series of 98 headache patients and 26 sex- and age-balanced controls were evaluated. Acute allodynia (AA) was assessed by Jakubowski questionnaire, and interictal allodynia (IA) by a skin test with calibrated monofilaments. AA is widely known as a symptom more present in migraine than in TTH spectrum: in our study this was confirmed only in cases of episodic attacks. When headache index rises towards chronicization, the prevalence of AA increases in both headache spectrums (χ2 13.55; p < 0.01). AA was associated with IA only in cases of chronic headache. When headache becomes chronic, mostly in presence of medication overuse, interictal CPT decreases and IA prevalence increases (χ2 20.44; p < 0.01), with closer association than AA. In MOH patients there were no significant differences depending on the diagnosis of starting headache (migraine or tension type headache) and, in both groups, we found the overuse of analgesics plays an important role: intake of more than one daily drug dramatically reduces the CPT (p < 0.05). Thus, when acute allodynia increases frequency, worsens or appears for the first time in patients with a long-standing history of chronic headache, it could reasonably suggest that the reduction of CPT had started, without using a specific practical skin test but simply by questioning clinical headache history. In conclusion, these results indicate that the role of medication overuse is more important than chronicization in lowering CPT, and suggest that prolonged periods of medication overuse can interfere with pain perception by a reduction of the pain threshold that facilitates the onset of every new attack leading to chronicization

The young stellar population at the center of NGC 205

Context. NGC 205 is a peculiar dwarf elliptical galaxy hosting in its center a population of young blue stars. Their origin is still matter of debate, the central fresh star formation activity possibly being related to dynamical interactions between NGC 205 and M31. Aims. The star formation history in the central 30\arcsec ($\sim$120 pc) around the NGC 205 central nucleus is investigated in order to obtain clues to the origin of the young stellar population. Methods. Deep HST/ACS CCD photometry is compared with theoretical isochrones and luminosity functions to characterize the stellar content of the region under study and compute the recent SF rate. Results. Our photometry reveals a previously undetected blue plume of young stars clearly distinguishable down to I$\simeq$26. Our analysis suggests that 1.9$\times10^5$ M$_\odot$ were produced between approximately 62 Myr and 335 Myr ago in the NGC 205 inner regions, with a latest minor episode occurring $\sim$25 Myr ago. This implies a star formation rate of $\sim7\times10^{-4}$ M$_\odot$/yr over this period. Conclusions. The excellent fit of the observed luminosity function of young main sequence stars obtained with a model having a constant star formation rate argues against a tidally triggered star formation activity over the last $\sim$300 Myr. Rather, a constant SF may be consistent with NGC 205 being on its first interaction with M 31.Comment: 5 pages, 2 figures, accepted for publication in A&A letter

Efficacy and Tolerability of Lapatinib in the Management of Breast Cancer

Approximately 20%–25% of all breast cancers over express a key cell surface growth factor receptor known as HER2. HER2 plays a key role in cell growth and proliferation and is linked to worse clinical outcomes, making it a logical therapeutic target. The first HER2 targeted drug to be approved by the FDA, was the humanized monoclonal antibody trastuzumab, after it showed improvements in survival in the adjuvant setting, and delayed time to progression in the metastatic setting. Although highly effective, for reasons that are not clear, some patients display resistance to trastuzumab. Lapatinib is an oral, small molecule tyrosine kinase inhibitor, that inhibits both the HER1 ahd HER2 receptors and may be able to overcome trastuzumab resistance. Lapatinib is approved in the second line setting for use in combination with capecitabine or with letrozole. In this review, we will discuss the indications, concerns or any issues with regards to the drug

Favorable outcome of early treatment of new onset child and adolescent migraine-implications for disease modification.

There is evidence that the prevalence of migraine in children and adolescents may be increasing. Current theories of migraine pathophysiology in adults suggest activation of central cortical and brainstem pathways in conjunction with the peripheral trigeminovascular system, which ultimately results in release of neuropeptides, facilitation of central pain pathways, neurogenic inflammation surrounding peripheral vessels, and vasodilatation. Although several risk factors for frequent episodic, chronic, and refractory migraine have been identified, the causes of migraine progression are not known. Migraine pathophysiology has not been fully evaluated in children. In this review, we will first discuss the evidence that early therapeutic interventions in the child or adolescent new onset migraineur, may halt or limit progression and disability. We will then review the evidence suggesting that many adults with chronic or refractory migraine developed their migraine as children or adolescents and may not have been treated adequately with migraine-specific therapy. Finally, we will show that early, appropriate and optimal treatment of migraine during childhood and adolescence may result in disease modification and prevent progression of this disease