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Hubble Space Telescope's (HST) Space Telescope Imaging Spectrograph (STIS) targeted 556 stars in a long-running program called Next Generation Spectral Library (NGSL) via proposals GO9088, GO9786, GO10222, and GO13776. Exposures through three low resolution gratings provide wavelength coverage from 0.2 $< \lambda <$ 1 $\mu$m at $\lambda/\Delta\lambda\sim$ 1000, providing unique coverage in the ultraviolet (UV). The UV grating (G230LB) scatters red light and this results in unwanted flux that becomes especially troubling for cool stars. We applied scattered light corrections based on \cite{2022stis.rept....5W} and flux corrections arising from pointing errors relative to the center of the 0\farcs2 slit. We present 514 fully reduced spectra, fluxed, dereddened, and cross-correlated to zero velocity. Because of the broad spectral range, we can simultaneously study H$\alpha$ and Mg II $\lambda$2800, indicators of chromospheric activity. Their behaviours are decoupled. Besides three cool dwarfs and one giant with mild flares in H$\alpha$, only Be stars show strong H$\alpha$ emission. Mg2800 emission, however, strongly anti-correlates with temperature such that warm stars show absorption and stars cooler than $5000 \: \! \rm{K}$ universally show chromospheric emission regardless of dwarf/giant status or metallicity. Transformed to Mg2800 flux emerging from the stellar surface, we find a correlation with temperature with approximately symmetric astrophysical scatter, in contrast to other workers who find a basal level with asymmetric scatter to strong values. Unsurprisingly, we confirm that Mg2800 activity is variable., Comment: 19 pages, 20 figures, 3 tables. Full version of table 3 is available online at https://archive.stsci.edu/hlsp/lowlib

The G230LB grating used with STIS's CCD detector scatters red light. In red objects, the scattered light mingles with the ultraviolet signal, causing spurious short-wavelength flux and weakening absorption features. Recent calibration observations characterize the scattered light using duplicate observations with the MAMA detector and similar grating G230L. The full two-dimensional spectrum contains little helpful information to mitigate the scattered light problem. For one-dimensional, extracted spectra, the scattered light can be approximately modeled as a ramped pedestal whose amplitude is proportional to the object's V-band flux. We present formulae for scattered light corrections. For stars warmer than G0 spectral type, correction is superfluous. Off-slit-center positioning appears not to affect the properties of the scattered light. Therefore, we are able to extrapolate correction formulae for extended objects from the point source formulae. Polynomials for flux corrections due to off-center slit positioning in the 0.2 arcsec slit are also tabulated., Comment: 30 pages, 17 figures

We investigate reheating in the string-theory-motivated K\"ahler Moduli Inflation I (KMII) potential, coupled to a light scalar field $\chi$ and produce constraints and forecasts based on Cosmic Microwave Background (CMB) and gravitational wave observables. We implement a Markov Chain Monte Carlo (MCMC) sampling method to compute the adopted model's parameter ranges allowed by the current CMB observations. Floquet analysis and numerical lattice simulations are performed to analyze the nonlinear effects of the model's (p)reheating phase. We derive bounds on the $\Lambda$CDM parameters $A_s$, $n_s$, $n_{\mathrm{run}}$, and $r$ based on \textit{Planck} results, finding that correlations between model parameters severely constrain the range of these parameters allowed within this model. While the KMII potential's non-vanishing minimum may provide a possible source for the observed dark energy density $\rho_{\mathrm{DE}}$ this cannot be tested with current observations. We estimate the $95\%$ CI bounds on the inflaton mass $m_{\phi}$ and reheating temperature $T_{\mathrm{reh}}$ to be $2.1 \times 10^{13} \, \mathrm{GeV} \lesssim m_{\phi} \lesssim 3.2 \times 10^{13} \, \mathrm{GeV}$ and $T_{\mathrm{reh}} \gtrsim 1.8 \times 10^{3} \, \mathrm{GeV}$, respectively. We observe {both} self-resonance and parametric resonance instability band structures in our Floquet analysis results. Finally, we do not observe any formation of oscillon configurations in our lattice simulations; however, our results predict a stochastic gravitational wave background generated during preheating that would be observable today in the $10^{9}$ - $10^{11} \, \mathrm{Hz}$ frequency range., Comment: 24 pages, 12 figures, 1 table

In this talk, I discuss the effects, viability, and predictions of the string-theory-motivated K\"ahler Moduli Inflation I (KMII) potential, coupled to a light scalar field $\chi$, which can provide a possible source for today's dark energy density due to the potential's non-vanishing minimum. Although the model is consistent with the current measured Cosmic Microwave Background (CMB) data, tighter constraints from future observations are required to test the viability of the KMII potential with its minimum equivalent to the observed cosmological constant's energy density $\rho_{\Lambda_{\mathrm{obs}}}$. We implement a Markov Chain Monte Carlo (MCMC) sampling method to compute the allowed model parameter ranges and bounds on the inflaton's mass $m_{\phi}$ and reheating temperature $T_{\mathrm{reh}}$. Additionally, our lattice simulations predict stochastic gravitational-wave backgrounds generated during the inflaton oscillations that would be observable today in the $10^{9}$-$10^{11} \, \mathrm{Hz}$ frequency range. All the results and details will be included in our upcoming paper with the same title., Comment: 6 pages, 3 figures. Contribution to the 2021 Gravitation session of the 55th Rencontres de Moriond

Libraries of stellar spectra find many uses in astrophysics, from photometric calibration to stellar population synthesis. We present low resolution spectra of 40 stars from 0.2 micrometers (ultraviolet) to 1.0 micrometers (near infrared) with excellent fluxing. The stars include normal O-type stars, helium-burning stars, and post-asymptotic giant branch (PAGB) stars. Spectra were obtained with the Space Telescope Imaging Spectrograph (STIS) installed in the Hubble Space Telescope (HST) using three low resolution gratings, G230LB, G430L, and G750L. Cosmic ray hits and fringing in the red were corrected. A correction for scattered light was applied, significant only for our coolest stars. Cross-correlation was used to bring the spectra to a common, final, zero velocity wavelength scale. Finally, synthetic stellar spectra were used to estimate line of sight dust extinction to each star, and a five-parameter dust extinction model was fit, or a one-parameter fit in the case of low extinction. These spectra dovetail with the similar Next Generation Stellar Library (NGSL) spectra, extending the NGSL's coverage of stellar parameters, and extending to helium burning stars and stars that do not fuse. The fitted dust extinction model showed considerable variation from star to star, indicating variations in dust properties for different lines of sight. Interstellar absorption lines are present in most stars, notably MgII., Comment: 13 pages, 5 figures. Accepted to Astronomy & Astrophysics, section 14. Catalogs and data

We consider a non-polynomial cubic spline to develop the classes of methods for the numerical solution of singularly perturbed two-point boundary value problems. The proposed methods are second and fourth order accurate and applicable to problems both in singular and non-singular cases. Numerical results are given to illustrate the efficiency of our methods and compared with the methods given by different authors., Comment: 11 pages, 0 figure; Numerical Solution of Boundary Value Problems for Ordinary Differential Equations, Prentice-Hall, Englewood Cliffs, NJ, 1988