Astrobites as a Community-led Model for Education, Science Communication, and Accessibility in Astrophysics

Support for early career astronomers who are just beginning to explore astronomy research is imperative to increase retention of diverse practitioners in the field. Since 2010, Astrobites has played an instrumental role in engaging members of the community -- particularly undergraduate and graduate students -- in research. In this white paper, the Astrobites collaboration outlines our multi-faceted online education platform that both eases the transition into astronomy research and promotes inclusive professional development opportunities. We additionally offer recommendations for how the astronomy community can reduce barriers to entry to astronomy research in the coming decade

Reverberation Mapping of the Kepler-Field AGN KA1858+4850

KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among the brightest active galaxies monitored by the Kepler mission. We have carried out a reverberation mapping campaign designed to measure the broad-line region size and estimate the mass of the black hole in this galaxy. We obtained 74 epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m telescope from February to November of 2012, and obtained complementary V-band images from five other ground-based telescopes. We measured the Hbeta light curve lag with respect to the V-band continuum light curve using both cross-correlation techniques (CCF) and continuum light curve variability modeling with the JAVELIN method, and found rest-frame lags of CCF = 13.53+2.03 2.32 days and JAVELIN = 13.15+1.08 1.00 days. The Hbeta root-mean-square line profile has a width of sigma line = 770 +/- 49 km s(exp -1). Combining these two results and assuming a virial scale factor of f = 5.13, we obtained a virial estimate of M(sub BH) = 8.06+1.59 1.72 10(exp 6) solar mass for the mass of the central black hole and an Eddington ratio of L/L(sub Edd) (is) approx. 0.2. We also obtained consistent but slightly shorter emission-line lags with respect to the Kepler light curve. Thanks to the Kepler mission, the light curve of KA1858+4850 has among the highest cadences and signal-to-noise ratios ever measured for an active galactic nucleus; thus, our black hole mass measurement will serve as a reference point for relations between black hole mass and continuum variability characteristics in active galactic nuclei

STELLAR POPULATION MODELS AND INDIVIDUAL ELEMENT ABUNDANCES. II. STELLAR SPECTRA AND INTEGRATED LIGHT MODELS

ABSTRACT The first paper in this series explored the effects of altering the chemical mixture of the stellar population on an element-by-element basis on stellar evolutionary tracks and isochrones to the end of the red giant branch. This paper extends the discussion by incorporating the fully consistent synthetic stellar spectra with those isochrone models in predicting integrated colors, Lick indices, and synthetic spectra. Older populations display element ratio effects in their spectra at higher amplitude than younger populations. In addition, spectral effects in the photospheres of stars tend to dominate over effects from isochrone temperatures and lifetimes, but, further, the isochrone-based effects that are present tend to fall along the age-metallicity degeneracy vector, while the direct stellar spectral effects usually show considerable orthogonality

Reverberation Mapping of the Kepler-Field AGN KA1858+4850

KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among the brightest active galaxies monitored by the Kepler mission. We have carried out a reverberation mapping campaign designed to measure the broad-line region size and estimate the mass of the black hole in this galaxy. We obtained 74 epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m telescope from February to November of 2012, and obtained complementary V-band images from five other ground-based telescopes. We measured the H-beta light curve lag with respect to the V-band continuum light curve using both cross-correlation techniques (CCF) and continuum light curve variability modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53 (+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s. Combining these two results and assuming a virial scale factor of f = 5.13, we obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also obtained consistent but slightly shorter emission-line lags with respect to the Kepler light curve. Thanks to the Kepler mission, the light curve of KA1858+4850 has among the highest cadences and signal-to-noise ratios ever measured for an active galactic nucleus; thus, our black hole mass measurement will serve as a reference point for relations between black hole mass and continuum variability characteristics in active galactic nuclei

The Normative Justifications of Regret

Regret is a negative emotion that we generally experience after acting in ways contrary to our normative standards. Many scholars argue that this emotion has little, if any, practical or moral justification. As a result, it is on-balance unwarranted. Some scholars argue that regret is simply adding an additional pain to the first pain (when the regretful action was made) and is therefore impractical and unreasonable (Bittner 1992). Others argue that most of the regret we experience is inappropriate. If we regret what happens in the past from our current psychological and normative framework, it is inappropriate because we are no longer the same person, in the relevant way, who transgressed (McQueen 2017). However, little research has directly addressed the normative and practical justification of regret from the standpoint of one’s current value system. My project considers how regret should be viewed and why it is valuable. It also reorients the literature toward a more straightforward understanding of regret and regretting that most people appear to experience. In Chapter 1, I consider the regret skeptic and the common objections to regret. In Chapter 2, I consider how regret has been misunderstood and seek to consolidate a coherent and consistent definition. In Chapter 3, I defend regret on the grounds that there is value in acknowledging the regretful act because of the way it activates and reorients us to what we value. I also show that there is value in learning from regret. This not only applies to making better choices in the future but also to improving our character as a result. In Chapter 4, I defend the view that being able to display regret is a social commodity because of its regulative and symbolic functions. The regulative and symbolic effects of regret are useful in our social and legal practices. It is only when we are in a position to consider the normative and practical benefits of regret that we are able to consider whether or not it is worth the pain

The properties of genome conformation and spatial gene interaction and regulation networks of normal and malignant human cell types.

The spatial conformation of a genome plays an important role in the long-range regulation of genome-wide gene expression and methylation, but has not been extensively studied due to lack of genome conformation data. The recently developed chromosome conformation capturing techniques such as the Hi-C method empowered by next generation sequencing can generate unbiased, large-scale, high-resolution chromosomal interaction (contact) data, providing an unprecedented opportunity to investigate the spatial structure of a genome and its applications in gene regulation, genomics, epigenetics, and cell biology. In this work, we conducted a comprehensive, large-scale computational analysis of this new stream of genome conformation data generated for three different human leukemia cells or cell lines by the Hi-C technique. We developed and applied a set of bioinformatics methods to reliably generate spatial chromosomal contacts from high-throughput sequencing data and to effectively use them to study the properties of the genome structures in one-dimension (1D) and two-dimension (2D). Our analysis demonstrates that Hi-C data can be effectively applied to study tissue-specific genome conformation, chromosome-chromosome interaction, chromosomal translocations, and spatial gene-gene interaction and regulation in a three-dimensional genome of primary tumor cells. Particularly, for the first time, we constructed genome-scale spatial gene-gene interaction network, transcription factor binding site (TFBS) - TFBS interaction network, and TFBS-gene interaction network from chromosomal contact information. Remarkably, all these networks possess the properties of scale-free modular networks

Aberrant Epigenetic Gene Regulation in Lymphoid Malignancies

In lymphoid malignancies, aberrant epigenetic mechanisms such as DNA methylation and histone modifications influence chromatin architecture and can result in altered gene expression. These alterations commonly affect genes that play important roles in the cell cycle, apoptosis, and DNA repair in non-Hodgkin lymphoma (NHL). The ability to identify epigenetic modifications to these important genes has increased exponentially due to advances in technology. As a result, there are well-defined, gene-specific epigenetic aberrations associated with NHL comprising follicular lymphoma (FL), mantle cell lymphoma (MCL), chronic lymphocytic leukemia (CLL), and diffuse large B-cell lymphoma (DLBCL). The identification of these genes is important because they may be used as biomarkers for prognosis, diagnosis and in developing improved treatment strategies. Also important, in the control of gene expression, is the packaging of DNA within the nucleus of a cell. This packaging can be distorted by epigenetic alterations and may alter the accessibility of certain regions of the genome in cancer cells. This review discusses the impact of known epigenetic aberration on the regulation of gene expression in NHL and provides insight into the spatial conformation of the genome (DNA packaging) in acute lymphoblastic leukemia

The contact matrices, correlation matrices, and difference matrices of chromosome 14 after applying normalization.

<p>(<b>A–D</b>) denote the contact matrices after removing reads mapped to multiple locations on the genome, (<b>E-H</b>) the contact matrices after applying SCN normalization method to the maps in (<b>A–D</b>), (<b>I–L</b>) the contact matrices after applying both genomic sequential distance based method and SCN to maps in (<b>A–D</b>), (<b>M–P</b>) the correlation matrices based on maps in E-H, and (<b>Q–T</b>) the difference matrices of between correlation matrices in M-P of normal and malignant samples.</p

The contact matrices, correlation matrices, and difference matrices of chromosome 14.

<p>This figure illustrates the original contact matrices, correlation matrices, and difference matrices of chromosome 14 for the normal human B-cell, human acute lymphoblastic leukemia B-cell, human MHH-CALL-4 B-ALL cell line, and human lymphoma RL cell-line. Heat maps (A-D) visualize the original number of contacts within the chromosome, (<b>E</b>-<b>H</b>) the Pearson’s correlation matrices generated from the original contact matrices, and (<b>I</b>-<b>L</b>) the absolute difference matrices generated from the correlation matrices.</p