Low Luminosity Research Articles

The Origin and Evolution of the Normal Type Ia SN 2018aoz with Infant-phase Reddening and Excess Emission

SN 2018aoz is a Type Ia SN with a B-band plateau and excess emission in infant-phase light curves ≲1 day after the first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN 2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show that the SN is intermediate between two subtypes of normal Type Ia: core normal and broad line. The excess emission may be attributable to the radioactive decay of surface iron-peak elements as well as the interaction of ejecta with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on Hα and He i favor a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [O i] and He i disfavors a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN 2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Fe ii] and [Ni ii]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1D models are incompatible with the infant-phase excess emission, color, and weak strength of nebular-phase [Ca ii]. Although the explosion processes of SN 2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear to be normal after ∼1 day.

MUSE crowded field 3D spectroscopy in NGC 300

Aims. We perform a deep survey of planetary nebulae (PNe) in the spiral galaxy NGC 300 to construct its planetary nebula luminosity function (PNLF). We aim to derive the distance using the PNLF and to probe the characteristics of the most luminous PNe. Methods. We analysed 44 fields observed with MUSE at the VLT, covering a total area of ∼11 kpc2. We find [O III]λ5007 sources using the differential emission line filter (DELF) technique. We identified PNe through spectral classification with the aid of the BPT diagram. The PNLF distance was derived using the maximum likelihood estimation technique. For the more luminous PNe, we also measured their extinction using the Balmer decrement. We estimated the luminosity and effective temperature of the central stars of the luminous PNe based on estimates of the excitation class and the assumption of optically thick nebulae. Results. We identify 107 PNe and derive a most-likely distance modulus $ (m-M)_0 = 26.48^{+0.11}_{-0.26} $ ($ d = 1.98^{+0.10}_{-0.23} $ Mpc). We find that the PNe at the PNLF cutoff exhibit relatively low extinction, with some high-extinction cases caused by local dust lanes. We present the lower limit luminosities and effective temperatures of the central stars for some of the brighter PNe. We also identify a few Type I PNe that come from a young population with progenitor masses > 2.5 M⊙ but do not populate the PNLF cutoff. Conclusions. The spatial resolution and spectral information of MUSE allow precise PN classification and photometry. These capabilities also enable us to resolve possible contamination by diffuse gas and dust, improving the accuracy of the PNLF distance to NGC 300.

O iii] 5007 Å Emission Line Width as a Surrogate for σ ∗ in Type 1 AGNs?

We present a study of the relation between the [O iii] 5007 Å emission line width (σ [OIII]) and stellar velocity dispersion (σ *), utilizing a sample of 740 type 1 active galactic nuclei (AGNs) with high-quality spectra at redshift z < 1.0. We find the broad correlation between the core component of the [O iii] emission line width () and σ * with a scatter of 0.11 dex for the low redshift (z < 0.1) sample; for redshift (0.3 < z < 1.0) AGNs, the scatter is larger, being 0.16 dex. We also find that the Eddington ratio (L bol/L Edd) may play an important role in the discrepancies between and σ *. As the L bol/L Edd increases, tends to be larger than σ *. By classifying our local sample with different minor-to-major axis ratios, we find that σ * is larger than for those edge-on spiral galaxies. In addition, we also find that the effects of outflow strength properties such as maximum outflow velocity () and the broader component of the [O iii] emission line width and line shift (σ [OIII,out] and V [OIII,out]) may play a major role in the discrepancies between and σ *. The discrepancies between and σ * are larger when , V [OIII,out], and σ [OIII,out] increase. Our results show that the outflow strengths may have significant effects on the differences between narrow-line region gas and stellar kinematics in AGNs. We suggest that caution should be taken when using as a surrogate for σ *. In addition, the substitute of for σ * could be used only for low luminosity AGNs.

Clustering dependence on Lyα luminosity from MUSE surveys at 3 &lt; z &lt; 6

We investigate the dependence of Lyα emitter (LAE) clustering on Lyα luminosity and connect the clustering properties of ≈L⋆ LAEs with those of much fainter ones, namely, ≈0.04L⋆. We use 1030 LAEs from the MUSE-Wide survey, 679 LAEs from MUSE-Deep, and 367 LAEs from the to-date deepest ever spectroscopic survey, the MUSE Extremely Deep Field. All objects have spectroscopic redshifts of 3 &lt; z &lt; 6 and cover a large dynamic range of Lyα luminosities: 40.15 &lt; log(LLyα/erg s−1) &lt; 43.35. We apply the Adelberger et al. K-estimator as the clustering statistic and fit the measurements with state-of-the-art halo occupation distribution (HOD) models. We find that the large-scale bias factor increases weakly with an increasing line luminosity. For the low-luminosity (log⟨LLyα/[erg s−1]⟩ = 41.22) and intermediate-luminosity (log⟨LLyα/[erg s−1]⟩ = 41.64) LAEs, we compute consistent bias factors blow = 2.43−0.15+0.15 and binterm. = 2.42−0.09+0.10, whereas for the high-luminosity (log⟨LLyα/[erg s−1]⟩ = 42.34) LAEs we calculated bhigh = 2.65−0.11+0.13. Consequently, high-luminosity LAEs occupy dark matter halos (DMHs) with typical masses of log(Mh/[h−1 M⊙]) = 11.09−0.09+0.10, while low-luminosity LAEs reside in halos of log(Mh/[h−1 M⊙]) = 10.77−0.15+0.13. The minimum masses to host one central LAE, Mmin, and (on average) one satellite LAE, M1, also vary with Lyα luminosity, growing from log(Mmin/[h−1M⊙]) = 10.3−0.3+0.2 and log(M1/[h−1 M⊙]) = 11.7−0.2+0.3 to log(Mmin/[h−1 M⊙]) = 10.7−0.3+0.2 and log(M1/[h−1 M⊙]) = 12.4−0.6+0.4 from low- to high-luminosity samples, respectively. The satellite fractions are ≲10% (≲20%) at 1σ (3σ) confidence level, supporting a scenario in which DMHs typically host one single LAE. We next bisected the three main samples into disjoint subsets to thoroughly explore the dependence of the clustering properties on LLyα. We report a strong (8σ) clustering dependence on Lyα luminosity, not accounting for cosmic variance effects, where the highest luminosity LAE subsample (log(LLyα/erg s−1) ≈ 42.53) clusters more strongly (bhighest = 3.13−0.15+0.08) and resides in more massive DMHs (log(Mh/[h−1M⊙] )= 11.43−0.10+0.04) than the lowest luminosity one (log(LLyα/erg s−1) ≈ 40.97), which presents a bias of blowest = 1.79−0.06+0.08 and occupies log(Mh/[h−1M⊙]) = 10.00−0.09+0.12 halos. We discuss the implications of these results for evolving Lyα luminosity functions, halo mass dependent Lyα escape fractions, and incomplete reionization signatures.

Thermodynamics of diamond formation from hydrocarbon mixtures in planets

Hydrocarbon mixtures are extremely abundant in the Universe, and diamond formation from them can play a crucial role in shaping the interior structure and evolution of planets. With first-principles accuracy, we first estimate the melting line of diamond, and then reveal the nature of chemical bonding in hydrocarbons at extreme conditions. We finally establish the pressure-temperature phase boundary where it is thermodynamically possible for diamond to form from hydrocarbon mixtures with different atomic fractions of carbon. Notably, here we show a depletion zone at pressures above 200 GPa and temperatures below 3000 K-3500 K where diamond formation is thermodynamically favorable regardless of the carbon atomic fraction, due to a phase separation mechanism. The cooler condition of the interior of Neptune compared to Uranus means that the former is much more likely to contain the depletion zone. Our findings can help explain the dichotomy of the two ice giants manifested by the low luminosity of Uranus, and lead to a better understanding of (exo-)planetary formation and evolution.

Combustion and mass loss behavior and characteristics of a single biomass pellet positioning at different orientations in a fixed bed reactor

This study aims to investigate the combustion characteristics and mass loss behaviors of rice straw and wheat straw biomass pellets experimentally in a laboratory fixed bed combustor under various operating conditions. High-speed photography was used to record images of the combustion process, and a sensitive balance was utilized for recording the particle mass history during the combustion process in addition to K-type thermocouples for temperature measurements. For both materials, the single pellet was exposed to various air temperatures and different flow rates of air. The orientation of the biomass pellet was positioned at various angles from 0 (horizontal), 30°, 45°, 60° (inclined), and 90° (parallel) to the hot air stream at different flow rates. Both glowing reactions and flameless ignition have been noticed in all experiments at all pellet orientations. All pellets experienced low and high luminosity volatiles without flames, followed by a bright radish color and short-lived combustion of the chars. Although the volatile contents of the two materials are identical, the volatile combustion duration of wheat straw (17–258 s) is less than that of rice straw (20–300 s), which could be due to differences in particle sizes, shapes, and structural compositions. The results also show that increased air temperatures lessen the time it takes for volatile and char to ignite and burn off. It also raises the temperature of surface ignition. Starting from the horizontal position and increasing the orientation angle of the pellet, the volatile and char ignition times increase up to 30° and then drop up to 90°, with angle 45° giving the lowest value. The same pattern was also noticed for volatile and char burnout times. The pellet horizontal position (0°) exhibits reduced combustion and mass loss (%) time intervals. The order of increasing the maximum temperature at the pellet surface was 30° > 60° > 90° angles. Increasing the air temperature reduces the times of char combustion, devolatilization, volatile burnout, and char burnout. As the air flow rate increases, the effect on the combustion parameters alternates between increasing and decreasing values.

Three-dimensional core-collapse supernovae with complex magnetic structures – II. Rotational instabilities and multimessenger signatures

ABSTRACT The gravitational collapse of rapidly rotating massive stars can lead to the onset of the low T/|W| instability within the central proto-neutron star (PNS), which leaves strong signatures in both the gravitational wave (GW) and neutrino emission. Strong large-scale magnetic fields are usually invoked to explain outstanding stellar explosions of rapidly rotating progenitors, but their impact on the growth of such instability has not yet been cleared. We analyse a series of three-dimensional magnetohydrodynamic models to characterize the effects of different magnetic configurations on the development of the low T/|W| and the related multimessenger features. In the absence of magnetic fields, we observe the growth on dynamical time-scales of the low T/|W|, associated with a strong burst of GW and a correlated modulation of the neutrino emission. However, models with a strong magnetic field show a quenching of the low T/|W|, due to a flattening of the rotation profile in the first ∼100 ms after shock formation caused by the magnetic transport of angular momentum. The associated GW emission is weakened by an order of magnitude, exhibits a broader spectral shape, and has no dominant feature associated with the PNS large-scale oscillation modes. Neutrino luminosities are damped along the equatorial plane due to a more oblate PNS, and the only clear modulation in the signal is due to Standing Accretion Shock Instability activity. Finally, magnetized models produce lower luminosities for νe than for $\bar{\nu }_e$, which is connected to a higher concentration of neutron-rich material in the PNS surroundings.

Intermediate-mass black holes: finding of episodic, large-scale, and powerful jet activity in a dwarf galaxy

ABSTRACT Dwarf galaxies are characterized by a very low luminosity and low mass. Because of significant accretion and ejection activity of massive black holes, some dwarf galaxies also host low-luminosity active galactic nuclei (AGNs). In a few dwarf AGNs, very long baseline interferometry (VLBI) observations have found faint non-thermal radio emission. SDSS J090613.77+561015.2 is a dwarf AGN owning an intermediate-mass black hole (IMBH) with a mass of $M_\mathrm{BH} = 3.6^{+5.9}_{-2.3}\times 10^5 \mathrm{ M}_{\odot }$ and showing a rarely seen two-component radio structure in its radio nucleus. To further probe their nature, i.e. the IMBH jet activity, we performed additional deep observations with the European VLBI Network (EVN) at 1.66 and 4.99 GHz. We find the more diffuse emission regions and structure details. These new EVN imaging results allow us to reveal a two-sided jet morphology with a size up to about 150 mas (projected length ∼140 pc) and a radio luminosity of about 3 × 1038 erg s−1. The peak feature has an optically thin radio spectrum and thus more likely represents a relatively young ejecta instead of a jet base. The EVN study on SDSS J090613.77+561015.2 demonstrates the existence of episodic, relatively large-scale, and powerful IMBH jet activity in dwarf AGNs. Moreover, we collected a small sample of VLBI-detected dwarf AGNs and investigated their connections with normal AGNs. We notice that these radio sources in the dwarf AGNs tend to have steep spectra and small linear sizes, and possibly represent ejecta from scaled-down episodic jet activity.

Line luminosities of Galactic and Magellanic Cloud Wolf–Rayet stars

ABSTRACT We provide line luminosities and spectroscopic templates of prominent optical emission lines of 133 Galactic Wolf–Rayet (WR) stars by exploiting Gaia DR3 parallaxes and optical spectrophotometry, and provide comparisons with 112 counterparts in the Magellanic Clouds. Average line luminosities of the broad blue (He ii λ4686, C iii λλ4647,51, N iii λλ4634,41, and N v λλ4603,20) and yellow (C iv λλ5801,12) emission features for WN, WN/C, WC, and WO stars have application in characterizing the WR populations of star-forming regions of distant, unresolved galaxies. Early-type WN stars reveal lower line luminosities in more metal-poor environments, but the situation is less clear for late-type WN stars. LMC WC4–5 line luminosities are higher than their Milky Way counterparts, with line luminosities of Magellanic Cloud WO stars higher than Galactic stars. We highlight other prominent optical emission lines, N iv λλ3478,85 for WN and WN/C stars, O iv λλ3403,13 for WC and WO stars, and O vi λλ3811,34 for WO stars. We apply our calibrations to representative metal-poor and metal-rich WR galaxies, IC 4870 and NGC 3049, respectively, with spectral templates also applied based on a realistic mix of subtypes. Finally, the global blue and C iv λλ5801,12 line luminosities of the Large Magellanic Clouds or LMCs (Small Magellanic Clouds) are 2.6 × 1038 erg s−1 (9 × 1036 erg s−1) and 8.8 × 1037 erg s−1 (4 × 1036 erg s−1), respectively, with the cumulative WR line luminosity of the Milky Way estimated to be an order of magnitude higher than the LMC.

Does a radio jet drive the massive multiphase outflow in the ultra-luminous infrared galaxy IRAS 10565 + 2448?

ABSTRACT We present new upgraded Giant Metrewave Radio Telescope H i 21-cm observations of the ultra-luminous infrared galaxy IRAS 10565 + 2448, previously reported to show blueshifted, broad, and shallow H i absorption indicating an outflow. Our higher spatial resolution observations have localized this blueshifted outflow, which is ∼ 1.36 kpc southwest of the radio centre and has a blueshifted velocity of $\sim 148\, \rm km\, s^{-1}$ and a full width at half maximum of $\sim 581\, \rm km\, s^{-1}$. The spatial extent and kinematic properties of the H i outflow are consistent with the previously detected cold molecular outflows in IRAS 10565 + 2448, suggesting that they likely have the same driving mechanism and are tracing the same outflow. By combining the multiphase gas observations, we estimate a total outflowing mass rate of at least $140\, \rm M_\odot \, yr^{-1}$ and a total energy loss rate of at least $8.9\times 10^{42}\, \rm erg\, s^{-1}$, where the contribution from the ionized outflow is negligible, emphasizing the importance of including both cold neutral and molecular gas when quantifying the impact of outflows. We present evidence of the presence of a radio jet and argue that this may play a role in driving the observed outflows. The modest radio luminosity $L_{\rm 1.4GHz}\, \sim 1.3\times 10^{23}\, {\rm W\, Hz^{-1}}$ of the jet in IRAS 10565 + 2448 implies that the jet contribution to driving outflows should not be ignored in low radio luminosity active galactic nuclei.

Radio Emission of Nearby Early-type Galaxies in the Low and Very Low Radio Luminosity Range

We analyze radio continuum emission of early-type galaxies with dynamical measurements of central supermassive black hole (SMBH) masses and well-characterized large-scale environments, but regardless of the exact level of the nuclear activity. The 1.4 GHz radio fluxes collected with ∼arcmin resolution for 62 nearby targets (distances ≲153 Mpc) correspond to low and very low monochromatic luminosities of L r ∼ 1035–1041 erg s−1. We quantify possible correlations between the radio properties with the main parameters of SMBHs, host galaxies, and hot gaseous halos, finding a general bimodality in the radio luminosity distribution, with the borderline between radio-bright and radio-dim populations at . We analyze the far-infrared data for the targets, finding that all radio-bright and over a half of the radio-dim sources are overluminous in radio wavelengths with respect to the far-infrared–radio correlation. High-resolution radio maps reveal that the overwhelming majority of radio-dim sources is unresolved on the arcsecond scale, while the bulk of radio-bright sources display extended jets and lobes of low- and intermediate-power radio galaxies; these jets dominate the radio emission of radio-bright objects. Regarding the origin of the radio emission of radio-dim sources, we discuss two main possibilities. One possibility is the advection-dominated accretion flow model, in which the radio and nuclear X-ray radiative outputs at very low accretion rates are both dominated by unresolved jets. The other possibility is that the radio-dim sources, unlike the radio-bright ones, are characterized by low values of SMBH spins, so that their radio emission is not related to the jets, but instead is due to a combination of star-forming processes and previous nuclear outbursts.

Relationship of the stable auroral red arcs height to solar activity. The observation results at the Yakutsk meridian

We presented the first results of triangulation measurements of the stable auroral red arcs height at the Yakutsk meridian in 2015–2020. The heights of the lower luminosity boundary in arcs of 350–370 km near the maximum and 250–290 km during the minimum of solar activity in the 24th cycle are obtained. The decrease of the red arcs height in the minimum years is due to the significant density decrease of the upper neutral atmosphere.

A Systematic Search for Short-period Close White Dwarf Binary Candidates Based on Gaia EDR3 Catalog and Zwicky Transient Facility Data

Galactic short-period close white dwarf binaries (CWDBs) are important objects for space-borne gravitational-wave (GW) detectors in the millihertz frequency bands. Due to the intrinsically low luminosity, only about 25 identified CWDBs are detectable by the Laser Interferometer Space Antenna (LISA), which are also known as verification binaries (VBs). The Gaia Early Data Release 3 (EDR3) provids a catalog containing a large number of CWDB candidates, which also includes parallax and photometry measurements. We crossmatch the Gaia EDR3 and Zwicky Transient Facility public data release 8, and apply period-finding algorithms to obtain a sample of periodic variables. The phase-folded light curves are inspected, and finally we obtain a binary sample containing 429 CWDB candidates. We further classify the samples into eclipsing binaries (including 58 HW Vir-type binaries, 65 EA-type binaries, 56 EB-type binaries, and 41 EW-type binaries) and ellipsoidal variations (209 ELL-type binaries). We discovered four ultrashort period binary candidates with unique light-curve shapes. We estimate the GW amplitude of all of our binary candidates, and calculate the corresponding signal-to-noise ratio (S/N) for TianQin and LISA. We find two (six) potential GW candidates with S/Ns greater than 5 in the nominal mission time of TianQin (LISA), which increases the total number of candidate VBs for TianQin (LISA) to 18 (31).

Investigating the Narrow-line Region Dynamics in Nearby Active Galaxies

We present dynamical models of the narrow-line region (NLR) outflows in the nearby Seyfert galaxies Mrk 3, Mrk 78, NGC 1068, and NGC 4151 using observations from the Hubble Space Telescope and Apache Point Observatory. We employ long-slit spectroscopy to map the spatially resolved outflow and rotational velocities of the ionized gas. We also perform surface brightness decompositions of host galaxy images to constrain the enclosed stellar mass distributions as functions of distance from the supermassive black holes (SMBHs). Assuming that the NLR gas is accelerated by active galactic nuclei (AGN) radiation pressure, and subsequently decelerated by the host galaxy and SMBH gravitational potentials, we derive outflow velocity profiles where the gas is launched in situ at multiple distances from the SMBH. We find a strong correlation between the turnover (from acceleration to deceleration) radii from our models, with the turnovers seen in the observed velocities and spatially resolved mass outflow rates for the AGN with bolometric luminosities > 1044 erg s−1. This consistency indicates that radiation pressure is the dominant driving mechanism behind the NLR outflows in these moderate-luminosity AGNs, with a force multiplier ∼500 yielding the best agreement between the modeled and observed turnover radii. However, in Meena et al. we found that this trend may not hold at lower luminosities, where our modeled turnover distance for NGC 4051 is much smaller than in the observed kinematics. This result may indicate that either additional force(s) are responsible for accelerating the NLR outflows in low-luminosity AGNs, or higher spatial resolution observations are required to quantify their turnover radii.

A burst storm from the repeating FRB 20200120E in an M81 globular cluster

ABSTRACT The repeating fast radio burst (FRB) source FRB 20200120E is exceptional because of its proximity and association with a globular cluster. Here we report 60 bursts detected with the Effelsberg telescope at 1.4 GHz. We observe large variations in the burst rate, and report the first FRB 20200120E ‘burst storm’, where the source suddenly became active and 53 bursts (fluence ≥0.04 Jy ms) occurred within only 40 min. We find no strict periodicity in the burst arrival times, nor any evidence for periodicity in the source’s activity between observations. The burst storm shows a steep energy distribution (power-law index α = 2.39 ± 0.12) and a bimodal wait-time distribution, with log-normal means of 0.94$^{+0.07}_{-0.06}$ s and 23.61$^{+3.06}_{-2.71}$ s. We attribute these wait-time distribution peaks to a characteristic event time-scale and pseudo-Poisson burst rate, respectively. The secondary wait-time peak at ∼1 s is ∼50 × longer than the ∼24 ms time-scale seen for both FRB 20121102A and FRB 20201124A – potentially indicating a larger emission region, or slower burst propagation. FRB 20200120E shows order-of-magnitude lower burst durations and luminosities compared with FRB 20121102A and FRB 20201124A. Lastly, in contrast to FRB 20121102A, which has observed dispersion measure (DM) variations of ΔDM &amp;gt; 1 pc cm−3 on month-to-year time-scales, we determine that FRB 20200120E’s DM has remained stable (ΔDM &amp;lt; 0.15 pc cm−3) over &amp;gt;10 months. Overall, the observational characteristics of FRB 20200120E deviate quantitatively from other active repeaters, but it is unclear whether it is qualitatively a different type of source.

Line-driven winds from variable accretion discs

ABSTRACTWe use numerical hydrodynamics simulations to study line-driven winds launched from an accreting α-disc. Building on previous work where the driving radiation field is static, we compute a time-dependent radiation flux from the local, variable accretion rate of the disc. We find that prior to the establishment of a steady state in the disc, variations of $\sim 15{{\ \rm per\ cent}}$ in disc luminosity correlate with variations of ∼ 2–3 in the mass flux of the wind. After a steady state is reached, when luminosity variations drop to $\sim 3{{\ \rm per\ cent}}$, these correlations vanish as the variability in the mass flux is dominated by the intrinsic variability of the winds. This is especially evident in lower luminosity runs where intrinsic variability is higher due to a greater prevalence of failed winds. The changing mass flux occurs primarily due to the formation of clumps and voids near the disc atmosphere that propagate out into the low velocity part of the flow, a process that can be influenced by local variations in disc intensity. By computing the normalized standard deviation of the mass outflow, we show that the impact of luminosity variations on mass outflow is more visible at higher luminosity. However, the absolute change in mass outflow due to luminosity increases is larger for lower luminosity models due to the luminosity-mass flux scaling relation becoming steeper. We further discuss implications for CVs and AGN and observational prospects.

Radio detections of two unusual cataclysmic variables in the VLA Sky Survey

ABSTRACT We report two new radio detections of cataclysmic variables (CVs), and place them in context with radio and X-ray detections of other CVs. We detected QS Vir, a low accretion-rate CV; V2400 Oph, a discless intermediate polar; and recovered the polar AM Her in the Very Large Array Sky Survey 2–4 GHz radio images. The radio luminosities of these systems are higher than typically expected from coronal emission from stars of similar spectral types, and neither system is expected to produce jets, leaving the origin of the radio emission a puzzle. The radio emission mechanism for these two CVs may be electron–cyclotron maser emission, synchrotron radiation, or a more exotic process. We compile published radio detections of CVs, and X-ray measurements of these CVs, to illustrate their locations in the radio–X-ray luminosity plane, a diagnostic tool often used for X-ray binaries, active galactic nuclei, and radio stars. Several radio-emitting CVs, including these two newly detected CVs, seem to lie near the principal radio/X-ray track followed by black hole X-ray binaries at low luminosity, suggesting additional complexity in classifying unknown systems using their radio and X-ray luminosities alone.

Twisted magnetic field in star formation processes of L1521 F revealed by submillimeter dual-band polarimetry using the James Clerk Maxwell Telescope

Abstract Understanding the initial conditions of star formation requires both observational studies and theoretical works taking into account the magnetic field, which plays an important role in star formation processes. Herein, we study the young nearby dense cloud core L1521 F [n(H2) ∼104−6 cm−3] in the Taurus Molecular Cloud. This dense core hosts a 0.2 M⊙ protostar, categorized as a very low luminosity object with complex velocity structures, particularly in the vicinity of the protostar. To trace the magnetic field within the dense core, we conducted high-sensitivity submillimeter polarimetry of the dust continuum at λ = 850 μm and 450 μm using the POL-2 polarimeter situated in front of the SCUBA-2 submillimeter bolometer camera on the James Clerk Maxwell Telescope. This was compared with millimeter polarimetry taken at λ = 3.3 mm with ALMA. The magnetic field was detected at λ = 850 μm in the peripheral region, which is threaded in a north–south direction, while the central region traced at λ = 450 μm shows a magnetic field with an east–west direction, i.e., orthogonal to that of the peripheral region. Magnetic field strengths are estimated to be ∼70 μG and 200 μG in the peripheral and central regions, respectively, using the Davis–Chandrasekhar–Fermi method. The resulting mass-to-flux ratio of three times larger than that of magnetically critical state for both regions indicates that L 1521 F is magnetically supercritical, i.e., gravitational forces dominate over magnetic turbulence forces. Combining observational data with magnetohydrodynamic simulations, detailed parameters of the morphological properties of this puzzling object are derived for the first time.

Thermal Energy and Luminosity Characterization of an Advanced Ignition System Using a Non-Intrusive Methodology in an Optically Accessible Calorimeter

To restrain the environmental impact of modern SI engines, igniters must guarantee stable combustions with low cycle-to-cycle variability in extreme operating conditions (high EGR, ultra-lean), via high energy release in the combustion chamber. The direct measurement of this energy is not trivial and requires a controlled environment. Luminosity detection is a non-intrusive diagnostic technique to indirectly measure the thermal energy released by the discharge on optically accessible apparatus. This work compares energy and luminosity produced by a plasma igniter in a constant volume vessel at realistic working conditions (ignition at 8 bar and air as a medium). A calibration factor can be defined to describe the thermal energy behavior as a function of the discharge luminosity and to give an assessment of such approach for its use in optically accessible engine. This study shows that thermal energy and luminosity are influenced by the gas type and related by a linear relationship for both air and nitrogen. The presence of oxygen resulted in discharges with reduced energy delivery to the medium and a lower discharge luminosity compared to nitrogen. This work outcome could improve the use of a non-intrusive methodology, based on luminosity detection, to characterize the igniter performance, exploitable for 3D-CFD.

EFFECT OF LEVEL OF PFD ON PHOTOSYNTHETIC PARAMETERS AND PRODUCTION OF STEVIOL GLYCOSIDES BY HYDROPONIC CULTURE FROM STEVIA REBAUDIANA BERTONI

Stevia rebaudiana produces steviol glycosides (GSt) 300 times sweeter higher than sugar cane. The problem is that the global demand is increasing and the agricultural production is insufficient. Is reported that Hydroponic cultivation and high irradiance increase the yield of S. rebaudiana and the production of steviol glycosides. This is due to the management and control of nutrition and the effect of light on the photosynthetic system, respectively. Therefore, the objective was to evaluate the effect on three levels of PFD (440.8, 383.9 and 273.2 μmol m-2 s) efficiency of photosystem PSII, and production of glycosides of steviol in S. rebaudiana var. Morita II at 40 and 90 days, using a NFT hydroponic culture (Nutrient Film Technique). The highest photosynthetic rate was recorded at 440.8 μmol m-2 s with 15.4 and 17.72 ppm CO2 min-1 g at 40 and 90 of culture days respectively and the higher content of steviol glycosides, with this same PFD, the lowest fluorescence emission occurred in PSII, while with low luminosity, the absorbed energy was harnessed more efficiently by the PSIIRC. The photosynthesis and production of steviol glycosides in S. rebaudiana were affected by level of PFD and culture time in a hydroponic system.