MMT observations of new extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey

We present 6.5-meter MMT spectrophotometry of 20 H II regions in 13 extremely metal-poor emission-line galaxies selected from the Data Release 5 of the Sloan Digital Sky Survey to have [O III] 4959/Hbeta < 1 and [N II] 6583/Hbeta < 0.05. The electron temperature-sensitive emission line [O III] 4363 is detected in 13 H II regions allowing a direct abundance determination. The oxygen abundance in the remaining H II regions is derived using a semi-empirical method. The oxygen abundance of the galaxies in our sample ranges from 12+logO/H ~ 7.1 to ~ 7.8, with 10 H II regions having an oxygen abundance lower than 7.5. The lowest oxygen abundances, 12+logO/H = 7.14+/-0.03 and 7.13+/-0.07, are found in two H II regions of the blue compact dwarf galaxy SDSSJ0956+2849=DDO 68, making it the second most-metal deficient emission-line galaxy known, after SBS 0335-052W.Comment: 28 pages, 3 figures. Accepted for publication in the Astrophysical Journa

Near-infrared spectroscopy of the Blue Compact Dwarf galaxy Markarian 59

We present near-infrared (NIR) spectroscopic observations of the blue compact dwarf (BCD) galaxy Mrk 59, obtained with the TripleSpec spectrograph mounted on the 3.5m APO telescope. The NIR spectrum of Mrk 59, which covers the 0.90 - 2.40 micron wavelength range, shows atomic hydrogen, molecular hydrogen, helium, sulfur and iron emission lines. The NIR data have been supplemented by a SDSS optical spectrum. We found extinction in the BCD to be low [A(V)=0.24 mag] and to be the same in both the optical and NIR ranges. The NIR light does not reveal hidden star formation. The H2 emission comes from dense clumps and the H2 vibrational emission line intensities can be accounted for by photon excitation. No shock excitation is needed. A CLOUDY photoinization model of Mrk 59 reproduces well the observed optical and NIR emission line fluxes. There is no need to invoke sources of ionization other than stellar radiation.The [FeII] 1.257 and 1.643 micron emission lines, often used as supernova shock indicators in low-excitation high-metallicity starburst galaxies, cannot play such a role in high-excitation low-metallicity HII regions such as Mrk 59.Comment: 23 pages, 3 figures, accepted for publication in the Astrophysical Journa

Performance gap of two users in downlink full-duplex cooperative NOMA

A full-duplex non-orthogonal multiple access (FD-NOMA) systems are expected to play a significant role in fifth generation (5G) networks, addressing spectrum efficiency and massive connections. In this regard, the feasibility of FD communications to improve spectrum utilization is main consideration in term of outage performance. Specifically, we derive exact formulas of outage probability for FD-NOMA, over Nakagami-m fading channels. Extensive analysis revealed that higher quality of channel leads to better performance. We verify expressions throughout Monte-Carlo simulations

Option pricing and CVA calculations using the Monte Carlo-Tree (MC-Tree) method

The thesis introduces a new method, the MC-Tree method, for pricing certain financial derivatives, especially options with high accuracy and efficiency. Our solution is to combine Monte Carlo (MC) method and Tree method by doing a mixing distribution on the tree, and the output is the compound distribution on the tree. The compound distribution in the tree output (after a logarithmic transformation of the asset prices) is not the ideal Gaussian distribution but has entropy values close to the maximum possible Gaussian entropy. We can get closer using entropy maximization. We introduce two correction techniques: distribution correction and bias correction to improve the accuracy and completeness of the model. The thesis presents an algorithm and numerical results for calculations of CVA on an American put option using the MC-Tree method. The MC-Tree method with the distribution correction technique significantly improves accuracy, resulting in practically exact solutions, compared to analytical solutions, at the tree depth $N=50$ or $100$ and MC-drawings $M=10^5$. The bias-correction technique makes the resulting tree model complete in the sense of financial mathematics and obtains the risk-neutral probability. Besides, we have obtained new formulae for the calculations of the entropy and the Kullback-Leibler divergence for rational densities and approximate entropy of finite Gaussian mixture

Exact Outage Performance Analysis of Amplify-and-forward-aware Cooperative NOMA

In this paper, new radio access scheme that combines Amplify-and-Forward (AF) relaying protocol and non-orthogonal multiple access (NOMA) system is introduced. In particular, different scenarios for fixed power allocation scheme is investigated. In addition, the outage probability of both weak and strong user is derived and provided in closed-form expressions. Such outage is investigated in high SNR scenario and comparison performance between these NOMA scenarios is introduced. Numerical simulations are offered to clarify the outage performance of the considered scheme if varying several parameters in the existing schemes to verify the derived formulas

Luminous Blue Variable Stars In The Two Extremely Metal-Deficient Blue Compact Dwarf Galaxies DDO 68 and PHL 293B

We present photometric and spectroscopic observations of two luminous blue variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD) galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72. These two BCDs are the lowest-metallicity galaxies where LBV stars have been detected, allowing to study the LBV phenomenon in the extremely low metallicity regime, and shedding light of the evolution of the first generation of massive stars born from primordial gas. We find that the strong outburst of the LBV star in DDO 68 occurred sometime between February 2007 and January 2008. We have compared the properties of the broad line emission in low-metallicity LBVs with those in higher metallicity LBVs. We find that, for the LBV star in DDO 68, broad emission with a P Cygni profile is seen in both H and He I emission lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are detected only in H lines. For both LBVs, no heavy element emission line such as Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal velocities of the stellar winds in both low-metallicity LBVs are high, ~800 km/s, a factor of ~4 higher than the terminal velocities of the winds in high-metallicity LBVs. This suggests that stellar winds at low metallicity are driven by a different mechanism than the one operating in high-metallicity winds.Comment: 26 pages, 5 figures, accepted for publication in the Astrophysical Journa

SBS 0335-052W: The Lowest-Metallicity Star-Forming Galaxy Known

We present 4-meter Kitt Peak telescope and 6.5-meter MMT spectrophotometry of the extremely low-metallicity galaxy SBS 0335-052W, the western companion of the blue compact dwarf galaxy SBS 0335-052E. These observations have been combined with published 10-meter Keck data to derive for the brightest region of SBS 0335-052W an oxygen abundance 12+logO/H=7.12+/-0.03. This makes SBS 0335-052W the lowest metallicity star-forming galaxy known in the local universe. Using a Monte Carlo technique, we fit the spectral energy distribution of SBS 0335-052W to derive the age of the oldest stars contributing to its optical light. We find that star formation in SBS 0335-052W began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical Journa

An introduction to Monte Carlo-Tree (MC-Tree) method

The article aims to introduce concepts in option pricing and risk management. Pricing and risk management is one of the fundamental problems in financial mathematics. Then readers may explore further to understand how to use mathematical models in pricing and risk management. More specifically, our research introduces a new method called Monte Carlo-Tree (MC-Tree), for option pricing and risk management with high accuracy

The Spitzer View of Low-Metallicity Star Formation: II. Mrk 996, a Blue Compact Dwarf Galaxy with an Extremely Dense Nucleus

(abridged) We present new Spitzer, UKIRT and MMT observations of the blue compact dwarf galaxy (BCD) Mrk 996, with an oxygen abundance of 12+log(O/H)=8.0. This galaxy has the peculiarity of possessing an extraordinarily dense nuclear star-forming region, with a central density of ~10^6 cm^{-3}. The nuclear region of Mrk 996 is characterized by several unusual properties: a very red color J-K = 1.8, broad and narrow emission-line components, and ionizing radiation as hard as 54.9 eV, as implied by the presence of the OIV 25.89 micron line. The nucleus is located within an exponential disk with colors consistent with a single stellar population of age >1 Gyr. The infrared morphology of Mrk 996 changes with wavelength. The IRS spectrum shows strong narrow Polycyclic Aromatic Hydrocarbon (PAH) emission, with narrow line widths and equivalent widths that are high for the metallicity of Mrk 996. Gaseous nebular fine-structure lines are also seen. A CLOUDY model requires that they originate in two distinct HII regions: a very dense HII region of radius ~580 pc with densities declining from ~10^6 at the center to a few hundreds cm^{-3} at the outer radius, where most of the optical lines arise; and a HII region with a density of ~300 cm^{-3} that is hidden in the optical but seen in the MIR. We suggest that the infrared lines arise mainly in the optically obscured HII region while they are strongly suppressed by collisional deexcitation in the optically visible one. The hard ionizing radiation needed to account for the OIV 25.89 micron line is most likely due to fast radiative shocks propagating in an interstellar medium. A hidden population of Wolf-Rayet stars of type WNE-w or a hidden AGN as sources of hard ionizing radiation are less likely possibilities.Comment: 48 pages, 13 figures, accepted for publication in the Astrophysical Journa