Adam Kobelski

Thermal Evolution of Hyperon-Mixed Neutron Stars

With the impressive amount of data that have poured out from Chandra and XMM/Newton X-ray space missions, as well as the lower energy band observations, we are now in the position where careful comparison of neutron star thermal evolution theories with observations will help us to distinguish among various competing theories. For instance, the latest theoretical and observational developments probably will contradict with the direct Urca cooling of neutron stars without some exotic particles. In this paper, we investigate one of the remaining possible fast cooling scenarios—direct Urca cooling of neutron stars in the hyperon-mixed phase. We conclude that this cooling scenario is a valid process if hyperon superfluidity is not too weak.

Calibrating Data from the Hinode /X-Ray Telescope and Associated Uncertainties

The X-Ray Telescope (XRT) onboard the Hinode satellite, launched 23 September 2006 by the Japan Aerospace Exploration Agency (JAXA), is a joint mission of Japan, the United States, and the United Kingdom to study the solar corona. In particular, XRT was designed to study solar plasmas with temperatures between 1 and 10 MK with ≈ 1″ pixels (≈ 2″ resolution). Prior to analysis, the data product from this instrument must be properly calibrated and data values quantified to accurately assess the information contained within. We present here the standard methods of calibration for these data. The calibration was performed on an empirical basis that uses the least complicated correction that accurately describes the data while suppressing spurious features. By analyzing the uncertainties remaining in the data after calibration, we conclude that the procedure is successful, because the remaining uncertainty after calibration is dominated by photon noise. This calibration software is available in the SolarSoft software library.

Sloan/Johnson‐Cousins/2MASS Color Transformations for Cool Stars

ABSTRACT We present multicolor transformations and photometric parallaxes for a sample of 40 low‐mass dwarfs selected from the Sloan Digital Sky Survey (SDSS) and the General Catalogue of Trigonometric Stellar Parallaxes. Our sample was reobserved at the Manastash Ridge Observatory (MRO) using both Sloan and Johnson‐Cousin filters, and color transformations between the two photometric systems were derived. A subset of the sample had previously measured Johnson‐Cousins photometry and parallaxes as well as 2MASS photometry. We observed these stars at MRO using Sloan filters and used these data to derive photometric parallax relations as well as SDSS/Johnson‐Cousins/2MASS color transformations. We present the data and derived transformations for use in future low‐mass‐star studies.

The versatile GBT astronomical spectrometer (VEGAS): Current status and future plans

The VEGAS multi-beam spectrometer (VEGAS) was built for the Green Bank Telescope (GBT) through a partnership between the National Radio Astronomy Observatory (NRAO) and the University of California at Berkeley. VEGAS is based on a Field Programmable Gate Array (FPGA) frontend and a heterogeneous computing backend comprised of Graphical Processing Units (GPUs) and CPUs. This system provides processing power to analyze up to 8 dual-polarization or 16 single-polarization inputs at bandwidths of up to 1.25 GHz per input. VEGAS was released for “shared-risk” observing in March 2014 and it became the default GBT spectral line backend in August 2014. Some of the early VEGAS observations include the Radio Ammonia Mid-Plane Survey, mapping of HCN/HCO+ in nearby galaxies, and a variety of radio-recombination line and pulsar projects. We will present some of the latest VEGAS science highlights.

Modeling Active Region Transient Brightenings Observed with X-Ray Telescope as Multi-stranded Loops

Strong evidence exists that coronal loops as observed in extreme ultraviolet and soft X-rays may not be monolithic isotropic structures, but can often be more accurately modeled as bundles of independent strands. Modeling the observed active region transient brightenings (ARTBs) within this framework allows for the exploration of the energetic ramifications and characteristics of these stratified structures. Here we present a simple method of detecting and modeling ARTBs observed with the Hinode X-Ray Telescope (XRT) as groups of zero-dimensional strands, which allows us to probe parameter space to better understand the spatial and temporal dependence of strand heating in impulsively heated loops. This partially automated method can be used to analyze a large number of observations to gain a statistical insight into the parameters of coronal structures, including the number of heating events required in a given model to fit the observations. In this article, we present the methodology and demonstrate its use in detecting and modeling ARTBs in a sample data set from Hinode/XRT. These initial results show that, in general, multiple heating events are necessary to reproduce observed ARTBs, but the spatial dependence of these heating events cannot yet be established.

FORWARD MODELING TRANSIENT BRIGHTENINGS AND MICROFLARES AROUND AN ACTIVE REGION OBSERVED WITH Hi-C

Small scale flare-like brightenings around active regions are among the smallest and most fundamental of energetic transient events in the corona, providing a testbed for models of heating and active region dynamics. In a previous study, we modeled a large collection of these microflares observed with Hinode/XRT using EBTEL and found that they required multiple heating events, but could not distinguish between multiple heating events on a single strand, or multiple strands each experiencing a single heating event. We present here a similar study, but with EUV data of Active Region 11520 from the High Resolution Coronal Imager (Hi-C) sounding rocket. Hi- C provides an order of magnitude improvement to the spatial resolution of XRT, and a cooler temperature sensitivity, which combine to provide significant improvements to our ability to detect and model microflare activity around active regions. We have found that at the spatial resolution of Hi-C (approximately 0.3 arcseconds), the events occur much more frequently than expected (57 events detected, only 1 or 2 expected), and are most likely made from strands of order 100 km wide, each of which is impulsively heated with multiple heating events. These findings tend to support bursty reconnection as the cause of the energy release responsible for the brightenings.