Show Emission Lines Research Articles

High-velocity Blue-shifted Fe xxv Heα Line during a Superflare of the RS Canum Venaticorum–type Star IM Peg

The Monitor of All-sky X-ray Image (MAXI) detected a superflare, releasing 5 × 1037 erg in 2−10 keV, of the RS CVn-type star IM Peg at 10:41 UT on 2023 July 23 with its Gas Slit Camera (2−30 keV). We conducted X-ray follow-up observations of the superflare with the Neutron Star Interior Composition Explorer (NICER; 0.2−12 keV) starting at 16:52 UT on July 23 until 06:00 UT on August 2. NICER X-ray spectra clearly showed emission lines of the Fe xxv Heα and Fe xxvi Lyα for ∼1.5 days since the MAXI detection. The Fe XXV Heα line was blueshifted with its maximum Doppler velocity reaching −2200 ± 600 km s−1, suggesting an upward-moving plasma during the flare, such as a coronal mass ejection (CME) and/or chromospheric evaporation. This is the first case that the Fe xxv Heα line is blueshifted during a stellar flare, and its velocity overwhelmingly exceeds the escape velocity of the star (−230 km s−1). One hour before the most pronounced blueshift detection, a signature of the reheating of the flare plasma was observed. We discuss the origin of the blueshift, a CME, or high-velocity chromospheric evaporation.

Chemical Enrichment Study of Abell 3112 Galaxy Cluster with XMM-Newton

Galaksi kümeleri, evrendeki kütleçekimsel olarak bağlı en büyük yapılardır. Her biri milyonlarca yıldıza sahip olan yüzlerce galaksi içeriyor olsalar da, galaksi kümelerini oluşturan baryonik maddenin büyük kısmı kümeye yayılmış olan sıcak, iyonize gaz halindedir (genel olarak "intracluster medium" veya basitçe "ICM" şeklinde bahsedilir). Sıcaklığı milyonkelvin mertebesine ulaşan ICM gazı X-ışını ışıması yapar. ICM gazının X-ışın tayfı, bize gazın kimyasal özellikleri ve ICM'de dağılımını bulmamızı sağlayan metal emisyon çizgileri de barındırır. Bu çalışmada, XMM-Newton European Photon Imaging Camera (EPIC) verilerini kullanarak zengin bir galaksi kümesi olan A3112 (z=0.07525)'nin kimyasal yapısını inceliyoruz. Modelimiz, çekirdekte yüksek metal bolluğu ve düşük kT değeri göstermekte, bu da A3112'nin rahatlamış ve soğuk çekirdekli bir küme olduğuna işaret etmektedir.

The PAU survey: classifying low-z SEDs using Machine Learning clustering

ABSTRACT We present an application of unsupervised Machine Learning clustering to the PAU survey of galaxy spectral energy distribution (SED) within the COSMOS field. The clustering algorithm is implemented and optimized to get the relevant groups in the data SEDs. We find 12 groups from a total number of 5234 targets in the survey at 0.01 < z < 0.28. Among the groups, 3545 galaxies (68 per cent) show emission lines in the SEDs. These groups also include 1689 old galaxies with no active star formation. We have fitted the SED to every single galaxy in each group with CIGALE. The mass, age, and specific star formation rates (sSFR) of the galaxies range from 0.15 < age/Gyr <11; 6 < log (M⋆/M⊙) <11.26, and −14.67 < log (sSFR/yr−1) <−8. The groups are well-defined in their properties with galaxies having clear emission lines also having lower mass, are younger and have higher sSFR than those with elliptical like patterns. The characteristic values of galaxies showing clear emission lines are in agreement with the literature for starburst galaxies in COSMOS and GOODS-N fields at low redshift. The star-forming main sequence, sSFR versus stellar mass and UVJ diagram show clearly that different groups fall into different regions with some overlap among groups. Our main result is that the joint of low- resolution (R ∼ 50) photometric spectra provided by the PAU survey together with the unsupervised classification provides an excellent way to classify galaxies. Moreover, it helps to find and extend the analysis of extreme ELGs to lower masses and lower SFRs in the local Universe.

Nuclear star cluster formation in star-forming dwarf galaxies

Nuclear star clusters (NSCs) are massive star clusters found in all types of galaxies from dwarfs to massive galaxies. Recent studies show that while low-mass NSCs in dwarf galaxies (Mgal < 109 M⊙) form predominantly out of the merger of globular clusters (GCs), high-mass NSCs in massive galaxies have assembled most of their mass through central enriched star formation. So far, these results of a transition in the dominant NSC formation channel have been based on studies of early-type galaxies and massive late-type galaxies. Here, we present the first spectroscopic analysis of a sample of nine nucleated late-type dwarf galaxies with the aim of identifying the dominant NSC formation pathway. We use integral-field spectroscopy data obtained with the Multi Unit Spectroscopic Explorer (MUSE) instrument to analyse the ages, metallicities, star formation histories, and star formation rates of the NSCs and their surroundings. Our sample includes galaxies with stellar masses Mgal = 107 − 109 M⊙ and NSC masses MNSC = 6 × 104 − 6 × 106 M⊙. Although all NSC spectra show emission lines, this emission is not always connected to star formation within the NSC, but rather to other regions along the line of sight. The NSC star formation histories reveal that metal-poor and old populations dominate the stellar populations in five NSCs, possibly stemming from the inspiral of GCs. The NSCs of the most massive galaxies in our sample show significant contributions from young and enriched populations that indicate additional mass growth through central star formation. Our results support previous findings of a transition in the dominant NSC formation channel with galaxy mass, showing that the NSCs in low-mass galaxies predominantly grow through the inspiral of GCs, while central star formation can contribute to NSC growth in more massive galaxies.

A multiwavelength study of the flat-spectrum radio quasar NVSS J141922−083830 covering four flaring episodes

ABSTRACT We present multiwavelength observations and a model for flat-spectrum radio quasar (FSRQ) NVSS J141922−083830, originally classified as a blazar candidate of unknown type (BCU II object) in the Third Fermi-LAT AGN Catalog. Relatively bright flares (>3 magnitudes) were observed on 2015 February 21 (MJD 57074) and 2018 September 8 (MJD 58369) in the optical band with the MASTER Global Robotic Nettelescopes. Optical spectra obtained with the Southern African Large Telescopeon 2015 March 1 (MJD 57082), during outburst, and on 2017 May 30 (MJD 57903), during quiescence, showed emission lines at 5325 Å and at ≈3630 Å that we identified as the Mg ii 2798 Å and C iii] 1909 Å lines, respectively, and hence derived a redshift $z$ = 0.903. Analysis of Fermi-Large Area Telescope (LAT) data was performed in the quiescent regime (5 yr of data) and during four prominent flaring states in 2014 February–April, 2014 October–November, 2015 February–March, and 2018 September. We present spectral and timing analysis with Fermi-LAT. We report a hardening of the gamma-ray spectrum during the last three flaring periods, with a power-law spectral index Γ = 2.0–2.1. The maximum gamma-ray flux level was observed on 2014 October 24 (MJD 56954) at (7.57 ± 1.83) × 10−7 ph cm−2 s−1. The multiwavelength spectral energy distribution (SED) during the 2015 February–March flare supports the earlier evidence of this blazar to belong to the FSRQ class. The SED can be well represented with a single-zone leptonic model with parameters typical of FSRQs, but also a hadronic origin of the high-energy emission cannot be ruled out.

MALS SALT-NOT Survey of MIR-selected Powerful Radio-bright AGN at 0 < z < 3.5

We present results of an optical spectroscopic survey using SALT and the Nordic Optical Telescope to build a Wide-field Infrared Survey Explorer mid-infrared color-based, dust-unbiased sample of powerful radio-bright (>200 mJy at 1.4 GHz) active galactic nuclei (AGN) for the MeerKAT Absorption Line Survey (MALS). Our sample has 250 AGN (median z = 1.8) showing emission lines, 26 with no emission lines, and 27 without optical counterparts. Overall, our sample is fainter (Δi = 0.6 mag) and redder (Δ(g−i) = 0.2 mag) than radio-selected quasars, and representative of fainter quasar population detected in optical surveys. About 20% of the sources are narrow-line AGN (NLAGN)–65% of these, at z < 0.5 are galaxies without strong nuclear emission, and 10% at z > 1.9, have emission line ratios similar to radio galaxies. The farthest NLAGN in our sample is M1513-2524 (z em = 3.132), and the largest radio source (size ∼330 kpc) is M0909-3133 (z em = 0.884). We discuss in detail 110 AGN at 1.9 < z < 3.5. Despite representing the radio loudest quasars (median R = 3685), their Eddington ratios are similar to the Sloan Digital Sky Survey quasars having lower R. We detect four C iv broad-absorption line (BAL) QSOs, all among AGN with least R, and highest black hole masses and Eddington ratios. The BAL detection rate (%) is consistent with that seen in extremely powerful (L 1.4GHz > 1025 W Hz−1) quasars. Using optical light curves, radio polarization, and γ-ray detections, we identify seven high-probability BL Lacertae objects. We also summarize the full MALS footprint to search for H i 21 cm and OH 18 cm lines at z < 2.

Host galaxy properties of quasi-periodically erupting X-ray sources

Context.Quasi-periodic X-ray eruptions (QPEs) are a recently discovered phenomenon, the nature of which remains unclear. Based on their discovery in active galactic nuclei (AGNs), explanations related to an AGN accretion disk or potentially a stellar tidal disruption event (TDE) have been put forward. Alternatives, including highly unequal mass compact object binaries, have also been proposed to explain their properties.Aims.We perform a systematic study of the five known QPE host galaxies with the aim of providing new insights as to their nature.Methods.We analysed new and archival medium resolution optical spectroscopy of the QPE hosts. We measured emission (and absorption) line fluxes, their ratios, and equivalent widths (EWs) to locate the QPE hosts on diagnostic diagrams. We also measured the velocity dispersion of the stellar absorption lines to estimate their black hole masses.Results.All QPE host galaxies show emission lines in their optical spectra. Based on their ratios and EWs, we find evidence for the presence of an AGN in all sources, including those previously reported as passive. We measure velocity dispersions between 36 and 90 km s−1, implying the presence of low mass (105−6.7 M⊙) black holes, consistent with literature findings. Finally, we find a significant over-representation (two out of the five sources, or a factor of 13−10+13) of quiescent Balmer strong (post-starburst) galaxies among QPE hosts.Conclusions.The presence of a narrow line region consistent with an AGN in all QPE host galaxies implies that a long-lived accretion flow likely plays an integral part in the QPE phenomenon. The strong over-representation of quiescent Balmer strong galaxies among QPE hosts can be naturally explained in both the TDE and interacting extreme mass ratio inspiral hypotheses.

A peculiar Type II QSO identified via broad-band detection of extreme nebular line emission

ABSTRACT We present S82-20, an unusual redshift ≈3 object identified in SDSS-Stripe 82 broad-band images. The rest-frame ultraviolet spectrum of S82-20 shows emission lines from highly ionized species, including He ii λ1640, and the C iv λλ1548, 1550 and O vi λλ1032, 1038 doublets. The high Ly α luminosity (3.5 × 1044 erg s−1), the high emission line equivalent widths (&amp;gt;200 Å for Ly α), the full width at half-maximum of the emission lines (&amp;lt;800 km s−1), and the high ionization O vi line strongly support the interpretation that S82-20 is a Type II Quasi-Stellar Objects (QSOs). However, photoionization models using Type II QSO do not fully explain the measured C iv/He ii line ratio, which requires either some contribution from star formation or high velocity shocks. Additionally, S82-20 is not detected at wavelengths longer than 2 μm, in tension with the expectation of isotropically infrared emission of a luminous QSO. We consider the possibility that S82-20 is a rare example of a changing-look QSO, observed in a temporarily low state, where the broad line region has faded, while the narrow line region still emits emission line. Otherwise, it may be a rare case of the short phase of the life of a massive galaxy, in which active star formation and accretion on to a supermassive black hole coexist.

Chandra X-Ray Observations of V830 Tau: A T Tauri Star Hosting an Evanescent Planet

Abstract The radial velocity study by Donati et al. (2016) reported the detection of a close-in giant planet in a 4.93 day orbit around the ∼2 Myr old weak-lined T Tauri star V830 Tau. Because of the stringent timescale constraints that a very young host star like V830 Tau would place on hot-Jupiter formation models and inward-migration mechanisms, independent confirmation of the planet’s existence is needed but so far has not been obtained. We present new Chandra X-ray observations of V830 Tau. The Chandra observations in combination with previous XMM-Newton observations reveal strong, variable X-ray emission with an X-ray luminosity spanning the range log L x = 30.10–30.87 erg s−1. Chandra High Energy Transmission Grating spectra show emission lines formed over a range of plasma temperatures from ∼4 MK (Ne ix) to ∼16 MK (S xv). At the separation of the reported planet (0.057 au) the X-ray flux is ∼106–107 times greater than the Sun’s X-ray flux at Jupiter. We provide estimates of the X-ray ionization and atmospheric heating rates at the planet’s separation and identify areas of uncertainty that will need to be addressed in any future atmospheric models.

The Massive Ancient Galaxies at z &gt; 3 NEar-infrared (MAGAZ3NE) Survey: Confirmation of Extremely Rapid Star Formation and Quenching Timescales for Massive Galaxies in the Early Universe*

Abstract We present near-infrared spectroscopic confirmations of a sample of 16 photometrically selected galaxies with stellar masses &gt;11 at redshift z &gt; 3 from the XMM-VIDEO and COSMOS-UltraVISTA fields using Keck/MOSFIRE as part of the Massive Ancient Galaxies At z &gt; 3 NEar-infrared (MAGAZ3NE) survey. Eight of the ultramassive galaxies (UMGs) have specific star formation rates (sSFR) &lt; 0.03 Gyr−1, with negligible emission lines. Another seven UMGs show emission lines consistent with active galactic nuclei and/or star formation, while only one UMG has sSFR &gt; 1 Gyr−1. Model star formation histories of these galaxies describe systems that formed the majority of their stars in vigorous bursts of several hundred megayear duration around during which hundreds to thousands of solar masses were formed per year. These formation ages of &lt;1 Gyr prior to observation are consistent with ages derived from measurements of D n (4000) and (Hδ). Rapid quenching followed these bursty star-forming periods, generally occurring less than 350 Myr before observation, resulting in post-starburst SEDs and spectra for half the sample. The rapid formation timescales are consistent with the extreme star formation rates observed in dusty starbursts observed with ALMA, suggesting that such dusty galaxies are progenitors of these UMGs. While such formation histories have been suggested in previous studies, the large sample introduced here presents the most compelling evidence yet that vigorous star formation followed by rapid quenching is almost certainly the norm for high-mass galaxies in the early universe. The UMGs presented here were selected to be brighter than K s = 21.7, raising the intriguing possibility that even (fainter) older quiescent UMGs could exist at this epoch.

UV spectroscopy confirms SU Lyn to be a symbiotic star

ABSTRACT SU Lyn, a star that ostensibly appears to be an unremarkable late M type giant, has recently been proposed to be a symbiotic star largely based on its hard X-ray properties. The star does not display, in low-resolution optical spectra, the high excitation lines typically seen in the spectra of symbiotic stars. In this work, ultraviolet (UV), optical, and near-infrared observations are presented, aimed at exploring and strengthening the proposed symbiotic classification for this star. Our far-UV 1300–1800 Å spectrum of SU Lyn, obtained with the ASTROSAT mission’s UVIT payload, shows emission lines of Si iv, C iv, O iii, and N iii in a spectrum typical of symbiotic stars. The UV spectrum robustly confirms SU Lyn’s symbiotic nature. The detection of high excitation lines in a high-resolution optical spectrum further consolidates its symbiotic nature. As is being recognized, the potential existence of other similar symbiotic systems could significantly impact the census of symbiotic stars in the Galaxy.

V1460 Her: a fast spinning white dwarf accreting from an evolved donor star

ABSTRACT We present time-resolved optical and ultraviolet (UV) spectroscopy and photometry of V1460 Her, an eclipsing cataclysmic variable with a 4.99-h orbital period and an overluminous K5-type donor star. The optical spectra show emission lines from an accretion disc along with absorption lines from the donor. We use these to measure radial velocities, which, together with constraints upon the orbital inclination from photometry, imply masses of $M_1=0.869\pm 0.006\, \mathrm{M}_\odot$ and $M_2=0.295\pm 0.004\, \mathrm{M}_\odot$ for the white dwarf and the donor. The radius of the donor, $R_2=0.43\pm 0.002\, \mathrm{\it R}_\odot$, is ≈50 per cent larger than expected given its mass, while its spectral type is much earlier than the M3.5 type that would be expected from a main-sequence star with a similar mass. Hubble Space Telescope (HST) spectra show strong N v 1240-Å emission but no C iv 1550-Å emission, evidence for CNO-processed material. The donor is therefore a bloated, overluminous remnant of a thermal time-scale stage of high mass transfer and has yet to reestablish thermal equilibrium. Remarkably, the HST UV data also show a strong 30 per cent peak-to-peak, $38.9\,$s pulsation that we explain as being due to the spin of the white dwarf, potentially putting V1460 Her in a similar category to the propeller system AE Aqr in terms of its spin frequency and evolutionary path. AE Aqr also features a post-thermal time-scale mass donor, and V1460 Her may therefore be its weak magnetic field analogue since the accretion disc is still present, with the white dwarf spin-up a result of a recent high accretion rate.

GASP XXIV. The History of Abruptly Quenched Galaxies in Clusters

Abstract The study of cluster post-starburst galaxies gives useful insights on the physical processes quenching the star formation in the most massive environments. Exploiting the Multi Unit Spectroscopic Explorer data of the GAs Stripping Phenomena in galaxies project, we characterize the quenching history of eight local cluster galaxies that were selected for not showing emission lines in their fiber spectra. We inspect the integrated colors, the Hβ rest-frame equivalent widths (EW), star-formation histories (SFHs), and luminosity-weighted age (LWA) maps finding no signs of current star formation throughout the disks of these early-spiral/S0 galaxies. All of them have been passive for at least 20 Myr, but their SF declined on different timescales. In most of them, the outskirts reached undetectable SFRs before the inner regions (“outside-in quenching”). Our sample includes three post-star-forming galaxies, two passive galaxies, and three galaxies with intermediate properties. The first population shows blue colors, deep Hβ in absorption (EW ≫ 2.8 Å), young ages (8.8 &lt; log(LWA (yr)) &lt; 9.2). Two of these galaxies show signs of a central SF enhancement before quenching. Passive galaxies have instead red colors, EW(Hβ) &lt; 2.8 Å, ages in the range 9.2 &lt; log(LWA (yr)) &lt; 10. Finally, the other galaxies are most likely in transition between a post-star-forming and passive phase, as they quenched in an intermediate epoch and have not lost all of the star-forming features yet. The outside-in quenching, the morphology, and kinematics of the stellar component, along with the position of these galaxies within massive clusters (σ cl = 550–950 km s − 1 ) point to a scenario in which ram pressure stripping has removed the gas, leading to quenching. Only the three most massive galaxies might alternatively have entered the clusters already quenched. These galaxies are therefore at the final stage of the rapid evolution galaxies undergo when they enter the cluster environment.

Double pulse laser induced breakdown spectroscopy at 600 bar water pressure

The demand for raw materials is growing and deep-sea mining is becoming increasingly important. It is of great interest to be able to analyze materials directly in the deep sea for mining or research applications. Laser induced breakdown spectroscopy (LIBS) is a laser-based, non-contact method for analyzing material in terms of its elemental composition. This paper presents the design of a LIBS system to be operated in a water depth of up to 6000 meters. A compact double pulse laser with adaptable pulse interval was developed to address different water depths. The complete LIBS setup was tested in a pressure chamber and shows emission lines from zinc up to a water pressure of 600 bar. To the best of our knowledge, this was the first LIBS measurement at 600 bar water pressure.

Structure and luminescent properties of new Dy3+/Eu3+/Sm3+-activated InNbTiO6 phosphors for white UV-LEDs

A series of novel Dy3+/Eu3+/Sm3+-activated InNbTiO6 phosphors have been prepared by conventional solid state reaction method. Based on the structure refinement, RE3+ ions are preferred to occupy the site of In3+ (2e) in the wolframite-type host lattice. According to their UV–visible diffusion reflectance spectra, the band gap and absorption property of un-doped InNbTiO6 sample can be tuned by the dopants. Under UV–visible light excitation, Dy3+/Eu3+/Sm3+ activators in this matrix mainly show emission lines originating from their characteristic f→f transitions. The optimal excitation and emission wavelength are 385 nm and 581 nm for Dy3+, 394 nm and 616 nm for Eu3+, 406 nm and 615 nm for Sm3+. Concentration quenching occurs at 0.06 for Dy3+, 0.06 for Eu3+, and 0.04 for Sm3+, ascribed to resonant q-q, q-q, and d-q interactions, respectively. The luminescence lifetimes are determined to be 0.13, 0.50, and 0.50 ms for InNbTiO6:0.06Dy3+, InNbTiO6:0.06Eu3+, and InNbTiO6:0.04Sm3+, respectively. The Dy3+, Eu3+, and Sm3+ doped phosphors exhibited yellowish-white, red, and orange-red luminescence, respectively. The quantum yields and thermal stability of representative phosphors have been investigated. Present work shows that these new phosphors are promising for application in UV-LED solid-state lighting devices.

Limits on stable iron in Type Ia supernovae from near-infrared spectroscopy

We obtained optical and near infrared spectra of Type Ia supernovae (SNe Ia) at epochs ranging from 224 to 496 days after the explosion. The spectra show emission lines from forbidden transitions of singly ionised iron and cobalt atoms. We used non-local thermodynamic equilibrium (NLTE) modelling of the first and second ionisation stages of iron, nickel, and cobalt to fit the spectra using a sampling algorithm allowing us to probe a broad parameter space. We derive velocity shifts, line widths, and abundance ratios for iron and cobalt. The measured line widths and velocity shifts of the singly ionised ions suggest a shared emitting region. Our data are fully compatible with radioactive 56Ni decay as the origin for cobalt and iron. We compare the measured abundance ratios of iron and cobalt to theoretical predictions of various SN Ia explosion models. These models include, in addition to 56Ni, different amounts of 57Ni and stable 54,56Fe. We can exclude models that produced only 54,56Fe or only 57Ni in addition to 56Ni. If we consider a model that has 56Ni, 57Ni, and 54,56Fe then our data imply that these ratios are 54,56Fe / 56Ni = 0.272 ± 0.086 and 57Ni / 56Ni = 0.032 ± 0.011.

Energy Transfer Behavior and Color-Tunable Properties of Ca2Al2SiO7:RE3+ (RE3+ = Tm3+, Dy3+, Tm3+/Dy3+) for White-Emitting Phosphors

Tm3+/Dy3+-codoped Ca2Al2SiO7 phosphors have been synthesized using a high-temperature solid-state reaction method. The crystal structure, x-ray diffraction patterns, and photoluminescence (PL) properties of the rare-earth (RE) ions, and energy transfer (ET) processes between RE ions, were investigated in detail. The quenching concentration of Tm3+ and Dy3+ singly doped in Ca2Al2SiO7 was determined to be 0.006 mol and 0.02 mol, respectively. Under excitation at 357 nm, Ca2Al2SiO7:Tm3+ phosphors showed emission lines of Tm3+ corresponding to 1D2 → 3F4 and 1G4 → 3H6 transitions. Efficient ET from Tm3+ to Dy3+ ions was observed, leading to color-tunable emissions of Ca2Al2SiO7:0.006Tm3+,xDy3+ (x = 0 mol to 0.02 mol) phosphors. Theoretical calculations revealed that the efficiency of the ET gradually increased with increase in the Dy3+ ion concentration, reaching a maximum of ∼ 42.1% at Tm3+ ion concentration of 0.006 mol. Furthermore, at 473 K, the quantum efficiency was calculated to be 79.8% at room temperature, confirming the good thermal stability of the Ca2Al2SiO7:0.006Tm3+,xDy3+ phosphors.

High excitation emission line nebula associated with an ultra-luminous X-ray source atz= 0.027 in the AKARI North Ecliptic Pole Deep Field

Aims. We report our finding of a high excitation emission line nebula associated with an Ultra Luminous X-ray source (ULX) at $z=$ 0.027, which we found in our Chandra observation of the AKARI North Ecliptic Pole (NEP) Deep Field. Methods. We present a Chandra X-ray and Gran Telescopio Canarias (GTC) optical spectral analysis of the ULX blob. We investigate the nature of the emission line nebula by using line ratio diagnostic diagrams, and its physical properties estimated from Spectral Energy Distribution (SED) fitting. Results. The optical spectrum of this ULX blob shows emission line ratios that are located on the borderlines between star-formation and Seyfert regimes in [OIII]/H$\beta$-[OI]/H$\alpha$, [OIII]/H$\beta$-[SII]/H$\alpha$ and [OIII]/H$\beta$-[OIII]/[OII] diagnostic diagrams. These are in contrast with those of a nearby blob observed with the same slit, which occupy the HII regimes. This result suggests that the ionization of the emission line nebula associated with the ULX is significantly contributed by energy input from the accretion power of the ULX, in addition to the star formation activity in the blob, suggesting the existence of an accretion disk in the ULX emitting UV radiation, or exerting shock waves.

Structural, electrochemical and magnetic properties of codoped (Cu, Mn) CdS nanoparticles with surfactant PVP

PVP capped with (Cu2+, Mn2+) codoped CdS and undoped nanoparticles were prepared by chemical precipitation method. The XRD patterns revealed that codoped CdS nanoparticles exhibit in cubic hawleyite mixed with hexagonal greenockite phase. The functional groups of the capping agent on codoped CdS surface were identified by FTIR. The UV–visible absorption spectra show significantl blue shift (501–514nm) and second excitonic absorption peak 241nm was observed only in the presence of a narrow size distribution. The increased optical band gap confirms the presence of quantum confinement. The photoluminescence (PL) emission spectrum shows emission line in the blue region. The emission band reveals that the measured band gap of around 2.7eV is greater than that of bulk CdS (2.42eV).T The average g–value, total number of spins (Ns) and covalency parameter (α2) were calculated from EPR results. The Cyclic Voltammetry curve of cathodic and anodic peaks shifted slightly to negative and positive potentials, respectively for electrode applications.

Keck/MOSFIRE spectroscopy of five ULX counterparts

We present H-band spectra of the candidate counterparts of five ULXs (two in NGC 925, two in NGC 4136, and Holmberg II X-1) obtained with Keck/MOSFIRE. The candidate counterparts of two ULXs (J022721+333500 in NGC 925 and J120922+295559 in NGC 4136) have spectra consistent with (M-type) red supergiants (RSGs). We obtained two epochs of spectroscopy of the candidate counterpart to J022721+333500, separated by 10 months, but discovered no radial velocity variations with a 2-$\sigma$ upper limit of 40 km/s. If the RSG is the donor star of the ULX, the most likely options are that either the system is seen at low inclination (< 40$^\circ$), or the black hole mass is less than 100 M$_\odot$, unless the orbital period is longer than 6 years, in which case the obtained limit is not constraining. The spectrum of the counterpart to J120922+295559 shows emission lines on top of its stellar spectrum, and the remaining three counterparts do not show absorption lines that can be associated with the atmosphere of a star; their spectra are instead dominated by emission lines. Those counterparts with RSG spectra may be used in the future to search for radial velocity variations, and, if those are present, determine dynamical constraints on the mass of the accretor.