Revealing the Population of Isolated, Massive Stars in the Central Molecular Zone

We report on the current census of isolated massive stars in the Galactic center region, including recently discovered objects. The latest discoveries were selected for their hard X-ray counterparts, detected with the Chandra X-ray Observatory; or for their Paschen-α emission-line excess, detected in narrowband images with HST/NICMOS. The confirmed stars span a wide range of massive star evolutionary stages: OIa, Of, Ofpe, LBV, WNh, WN, WNE, WC, and WCd. We suspect that the majority of the hard X-ray-emitting, massive stars we have identified are colliding-wind binaries, although some may be HMXBs. Most of the confirmed massive stars have no obvious association with the known, young stellar clusters, but some may have escaped from them. Extrapolation of their numbers suggests the existence of a massive star population, comparable in size to that contained within the clusters collectively, which could account for the integrated far-IR luminosity emerging from the central half-kiloparsec. This additional massive-star population may have been supplemented by the tidal disruption of stellar clusters, or suggests an alternate mode of isolated massive star formation operating in the Galactic center region. Future experiments will constrain their kinematics, binary characteristics, and mode of formation

Massive Young Stellar Objects in the Galactic Center. I. Spectroscopic Identification from Spitzer/IRS Observations

We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic Center (GC). Our sample of 107 YSO candidates was selected based on IRAC colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone (CMZ), which spans the central ~300 pc region of the Milky Way Galaxy. We obtained IRS spectra over 5um to 35um using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence of a 15.4um shoulder on the absorption profile of 15um CO2 ice, suggestive of CO2 ice mixed with CH3OH ice on grains. This 15.4um shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We show that 9 massive YSOs also reveal molecular gas-phase absorption from CO2, C2H2, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC. We fit YSO models to the observed spectral energy distributions and find YSO masses of 8 - 23 Msun, which generally agree with the masses derived from observed radio continuum emission. We find that about 50% of photometrically identified YSOs are confirmed with our spectroscopic study. This implies a preliminary star formation rate of ~0.07 Msun/yr at the GC.Comment: Accepted for publication in Ap

Infarto agudo de miocardio en paciente con bajo riesgo cardiovascular y lipoproteína (a) elevada. Reporte de caso

Lipoprotein(a) (Lp (a)) is a plasmatic lipid protein complex, which represents a risk factor for atherosclerotic cardiovascular disease (ASCVD). However, conventional lipid assays are unable to measure or estimate Lp (a) and there are no specific therapies approved to substantially reduce Lp (a) concentrations. We report the case of a 49-year-old man with low cardiovascular risk who developed an acute myocardial infarction with ST elevation probably due to elevation of Lp (a) is reported. The purpose of this case report is to highlight the detection and analysis of Lp (a) in the assessment of cardiovascular risk. In addition, current and emerging therapies are described in patients with elevated Lp (a).La lipoproteína (a) (Lp (a)) es un complejo proteico lipídico plasmático, que representa un factor de riesgo de enfermedad cardiovascular (ECV). Sin embargo, no se incluye la medición de Lp (a) en el perfil lipídico convencional y tampoco existen terapias específicas aprobadas para reducir sustancialmente las concentraciones de Lp (a). Se reporta el caso de un varón de 49 años con una estimación de bajo riesgo cardiovascular quien desarrolló infarto agudo de miocardio (IAM) con elevación de ST probablemente debido a elevación de Lp (a). Se presenta el caso para destacar la importancia de la detección y análisis de la Lp (a) en la evaluación del riesgo cardiovascular. Además, se describen terapias actuales y emergentes en pacientes con Lp (a) elevada

High-resolution Near-Infrared Images and Models of the Circumstellar Disk in HH 30

We present Hubble Space Telescope (HST) Near-Infrared Camera and Multi-object Spectrometer (NICMOS) observations of the reflection nebulosity associated with the T Tauri star HH 30. The images show the scattered light pattern characteristic of a highly inclined, optically thick disk with a prominent dustlane whose width decreases with increasing wavelength. The reflected nebulosity exhibits a lateral asymmetry in the upper lobe on the opposite side to that reported in previously published Wide Field Planetary Camera 2 (WFPC2) images. The radiation transfer model which most closely reproduces the data has a flared accretion disk with dust grains larger than standard interstellar medium grains by a factor of approximately 2.1. A single hotspot on the stellar surface provides the necessary asymmetry to fit the images and is consistent with previous modeling of the light curve and images. Photometric analysis results in an estimated extinction of Av>~80; however, since the photometry measures only scattered light rather than direct stellar flux, this a lower limit. The radiative transfer models require an extinction of Av = 7,900.Comment: Accepted for publication in Ap.