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- ItemDetection of Energy Cutoffs in Flare-accelerated Electrons(London : Institute of Physics Publ., 2021) Xia, Fanxiaoyu; Su, Yang; Wang, Wen; Wang, Linghua; Warmuth, Alexander; Gan, Weiqun; Li, YoupingEnergy cutoffs in electron distribution define the lower and upper limits on the energy range of energetic electrons accelerated in solar flares. They are crucial parameters for understanding particle acceleration processes and energy budgets. Their signatures have been reported in studies of flattened flare X-ray spectra, i.e., the impulsive emission of nonthermal bremsstrahlung from energetic electrons impacting ambient, thermal plasma. However, these observations have not provided unambiguous constraints on the cutoffs. Moreover, other processes may result in similar spectral features. Even the existence and necessity of cutoffs as physical parameters of energetic electrons have been under debate. Here we report a search for their signatures in flare-accelerated electrons with two approaches, i.e., in both X-ray spectra and solar energetic particle (SEP) events. These represent two different electron populations, but may contain information of the same acceleration process. By studying a special group of late impulsive flares, and a group of selected SEP events, we found evidence of cutoffs revealed in both X-ray spectra and SEP electron distributions. In particular, we found for the first time consistent low- and high-energy cutoffs in both hard X-ray-producing and escaping electrons in two events. We also showed the importance of high-energy cutoff in studies of spectral shapes. These results provide evidence of cutoffs in flare-accelerated energetic electrons and new clues for constraining electron distribution parameters and particle acceleration models.
- ItemOn the Use of Field RR Lyrae as Galactic Probes. V. Optical and Radial Velocity Curve Templates(London : Institute of Physics Publ., 2021) Braga, V.F.; Crestani, J.; Fabrizio, M.; Bono, G.; Sneden, C.; Preston, G. W.; Storm, J.; Kamann, S.; Latour, M.; Lala, H.; Lemasle, B.; Prudil, Z.; Altavilla, G.; Chaboyer, B.; Dall’Ora, M.; Ferraro, I.; Gilligan, C. K.; Fiorentino, G.; Iannicola, G.; Inno, L.; Kwak, S.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martínez-Vázquez, C.E.; Monelli, M.; Mullen, J.P.; Matsunaga, N.; Neeley, J.; Stetson, P. B.; Valenti, E.; Zoccali, M.We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including ≈20,000 high-, medium-, and low-resolution spectra for ≈10,000 RRLs. We provide the analytical forms of radial velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental - split into three period bins - and five first-overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H α , H β , H γ , H δ ). We tackled the long-standing problem of the reference epoch to anchor light-curve and RVC templates. For the V-band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are ∼35% to ∼45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC 3201 collected with MUSE at VLT. We found the cluster barycentric RV of V γ = 496.89 ± 8.37(error) ± 3.43 (standard deviation) km s-1, which agrees well with literature estimates.
- ItemOn the Origin of Hard X-Ray Emissions from the Behind-the-limb Flare on 2014 September 1(London : Institute of Physics Publ., 2021) Wu, Yihong; Rouillard, Alexis P.; Kouloumvakos, Athanasios; Vainio, Rami; Afanasiev, Alexandr N.; Plotnikov, Illya; Murphy, Ronald J.; Mann, Gottfried J.; Warmuth, AlexanderThe origin of hard X-rays and γ-rays emitted from the solar atmosphere during occulted solar flares is still debated. The hard X-ray emissions could come from flaring loop tops rising above the limb or coronal mass ejection shock waves, two by-products of energetic solar storms. For the shock scenario to work, accelerated particles must be released on magnetic field lines rooted on the visible disk and precipitate. We present a new Monte Carlo code that computes particle acceleration at shocks propagating along large coronal magnetic loops. A first implementation of the model is carried out for the 2014 September 1 event, and the modeled electron spectra are compared with those inferred from Fermi Gamma-ray Burst Monitor (GBM) measurements. When particle diffusion processes are invoked, our model can reproduce the hard electron spectra measured by GBM nearly 10 minutes after the estimated on-disk hard X-rays appear to have ceased from the flare site.
- ItemChemical Abundances and Ages of the Bulge Stars in APOGEE High-velocity Peaks(London : Institute of Physics Publ., 2017) Zhou, Yingying; Shen, Juntai; Liu, Chao; Li, Zhao-Yu; Mao, Shude; Kunder, Andrea; Rich, R. Michael; Zasowski, G.; Fernandez-Trincado, J. G.; Majewski, Steven R.; Lin, Chien-Cheng; Geisler, Doug; Tang, Baitian; Villanova, S.; Roman-Lopes, A.; Schultheis, M.; Nidever, David L.; Meza, Andrés; Pan, Kaike; Bizyaev, D. V.A cold, high-velocity (HV, ∼200 km s-1) peak was first reported in several Galactic bulge fields based on the Apache Point Observatory Galaxy Evolution Experiment (APOGEE) commissioning observations. Both the existence and the nature of the HV peak are still under debate. Here we revisit this feature with the latest APOGEE DR13 data. We find that most of the low-latitude bulge fields display a skewed Gaussian distribution with an HV shoulder. However, only 3 out of 53 fields show distinct HV peaks around 200 km s-1. The velocity distribution can be well described by Gauss-Hermite polynomials, except for the three fields showing clear HV peaks. We find that the correlation between the skewness parameter (h 3) and the mean velocity (), instead of a distinctive HV peak, is a strong indicator of the bar. It was recently suggested that the HV peak is composed of preferentially young stars. We choose three fields showing clear HV peaks to test this hypothesis using the metallicity, [α/M], and [C/N] as age proxies. We find that both young and old stars show HV features. The similarity between the chemical abundances of stars in the HV peaks and the main component indicates that they are not systematically different in terms of chemical abundance or age. In contrast, there are clear differences in chemical space between stars in the Sagittarius dwarf and the bulge stars. The strong HV peaks off-plane are still to be explained properly and could be different in nature.
- ItemAn Aligned Orbit for the Young Planet V1298 Tau b(London : Institute of Physics Publ., 2022) Johnson, Marshall C.; David, Trevor J.; Petigura, Erik A.; Isaacson, Howard T.; Van Zandt, Judah; Ilyin, Ilya; Strassmeier, Klaus; Mallonn, Matthias; Zhou, George; Mann, Andrew W.; Livingston, John H.; Luger, Rodrigo; Dai, Fei; Weiss, Lauren M.; Močnik, Teo; Giacalone, Steven; Hill, Michelle L.; Rice, Malena; Blunt, Sarah; Rubenzahl, Ryan; Dalba, Paul A.; Esquerdo, Gilbert A.; Berlind, Perry; Calkins, Michael L.; Foreman-Mackey, DanielThe alignment of planetary orbits with respect to the stellar rotation preserves information on their dynamical histories. Measuring this angle for young planets helps illuminate the mechanisms that create misaligned orbits for older planets, as different processes could operate over timescales ranging from a few megayears to a gigayear. We present spectroscopic transit observations of the young exoplanet V1298 Tau b; we update the age of V1298 Tau to be 28 ± 4 Myr based on Gaia EDR3 measurements. We observed a partial transit with Keck/HIRES and LBT/PEPSI, and detected the radial velocity anomaly due to the Rossiter-McLaughlin effect. V1298 Tau b has a prograde, well-aligned orbit, with λ=4-10+7 deg. By combining the spectroscopically measured v sin i∗ and the photometrically measured rotation period of the host star we also find that the orbit is aligned in 3D, ψ=8-7+4 deg. Finally, we combine our obliquity constraints with a previous measurement for the interior planet V1298 Tau c to constrain the mutual inclination between the two planets to be i mut = 0° ± 19°. This measurements adds to the growing number of well-aligned planets at young ages, hinting that misalignments may be generated over timescales of longer than tens of megayears. The number of measurements, however, is still small, and this population may not be representative of the older planets that have been observed to date. We also present the derivation of the relationship between i mut, λ, and i for the two planets.
- ItemSimulating Globular Clusters in Dark Matter Subhalos(London : Institute of Physics Publ., 2022) Carlberg, Raymond G.; Keating, Laura C.A cosmological zoom-in simulation that develops into a Milky Way-like halo begins at redshift 7. The initial dark matter distribution is seeded with dense star clusters of median mass 5 × 105 M o˙, placed in the largest subhalos present, which have a median peak circular velocity of 25 km s-1. Three simulations are initialized using the same dark matter distribution with the star clusters starting on approximately circular orbits having initial median radii 6.8, 0.14 kpc, and, at the exact center of the subhalos. The simulations are evolved to the current epoch at which time the median galactic orbital radii of the three sets of clusters are 30, 5, and 16 kpc, with the clusters losing about 2%, 50%, and 15% of their mass, respectively. Clusters beginning at small orbital radii have so much tidal forcing that they are often not in equilibrium. Clusters that start at larger subhalo radii have a velocity dispersion that declines smoothly to ≃20% of the central value at ≃20 half-mass radii. The clusters that begin in the subhalo centers can show a rise in velocity dispersion beyond 3-5 half-mass radii. That is, the clusters that form without local dark matter always have stellar-mass-dominated kinematics at all radii, whereas about 25% of the clusters that begin in subhalo centers have remnant local dark matter.
- ItemStellar Energetic Particle Transport in the Turbulent and CME-disrupted Stellar Wind of AU Microscopii(London : Institute of Physics Publ., 2022) Fraschetti, Federico; Alvarado-Gómez, Julián D.; Drake, Jeremy J.; Cohen, Ofer; Garraffo, CeciliaEnergetic particles emitted by active stars are likely to propagate in astrospheric magnetized plasma and disrupted by the prior passage of energetic coronal mass ejections (CMEs). We carried out test-particle simulations of ∼GeV protons produced at a variety of distances from the M1Ve star AU Microscopii by coronal flares or traveling shocks. Particles are propagated within a large-scale quiescent three-dimensional magnetic field and stellar wind reconstructed from measured magnetograms, and within the same stellar environment following the passage of a 1036 erg kinetic energy CME. In both cases, magnetic fluctuations with an isotropic power spectrum are overlayed onto the large-scale stellar magnetic field and particle propagation out to the two innnermost confirmed planets is examined. In the quiescent case, the magnetic field concentrates the particles into two regions near the ecliptic plane. After the passage of the CME, the closed field lines remain inflated and the reshuffled magnetic field remains highly compressed, shrinking the scattering mean free path of the particles. In the direction of propagation of the CME lobes the subsequent energetic particle (EP) flux is suppressed. Even for a CME front propagating out of the ecliptic plane, the EP flux along the planetary orbits highly fluctuates and peaks at ∼2-3 orders of magnitude higher than the average solar value at Earth, both in the quiescent and the post-CME cases.
- ItemLYRA. III. The Smallest Reionization Survivors(London : Institute of Physics Publ., 2022) Gutcke, Thales A.; Pfrommer, Christoph; Bryan, Greg L.; Pakmor, Rüdiger; Springel, Volker; Naab, ThorstenThe dividing line between galaxies that are quenched by reionization ("relics") and galaxies that survive reionization (i.e., continue forming stars) is commonly discussed in terms of a halo mass threshold. We probe this threshold in a physically more complete and accurate way than has been possible to date, using five extremely high resolution (Mtarget = 4 M⊙) cosmological zoom-in simulations of dwarf galaxies within the halo mass range (1–4) × 109 M⊙. The employed LYRA simulation model features resolved interstellar medium physics and individual, resolved supernova explosions. Interestingly, two out of five of the simulated dwarf galaxies lie close to the threshold mass but are neither full reionization relics nor full reionization survivors. These galaxies initially quench at the time of reionization but merely remain quiescent for ∼500 Myr. At z ∼ 5 they recommence star formation in a synchronous way and remain star-forming until the present day. The parallel timing indicates consistent sound-crossing and cooling times between the halos. While the star formation histories we find are diverse, we show that they are directly related to the ability of a given halo to retain and cool gas. Whereas the latter is most strongly dependent on the mass (or virial temperature) of the host halo at the time of reionization, it also depends on its growth history, the UV background (and its decrease at late times), and the amount of metals retained within the halo.
- ItemAn Absolute Calibration of the Near-infrared Period-Luminosity Relations of Type II Cepheids in the Milky Way and in the Large Magellanic Cloud(London : Institute of Physics Publ., 2022) Wielgórski, Piotr; Pietrzyński, Grzegorz; Pilecki, Bogumił; Gieren, Wolfgang; Zgirski, Bartłomiej; Górski, Marek; Hajdu, Gergely; Narloch, Weronika; Karczmarek, Paulina; Smolec, Radosław; Kervella, Pierre; Storm, Jesper; Gallenne, Alexandre; Breuval, Louise; Lewis, Megan; Kałuszyński, Mikołaj; Graczyk, Dariusz; Pych, Wojciech; Suchomska, Ksenia; Taormina, Mónica; Rojas Garcia, Gonzalo; Kotek, Aleksandra; Chini, Rolf; Pozo Nũnez, Francisco; Noroozi, Sadegh; Sobrino Figaredo, Catalina; Haas, Martin; Hodapp, Klaus; Mikołajczyk, Przemysław; Kotysz, Krzysztof; Moździerski, Dawid; Kołaczek-Szymański, PiotrWe present time-series photometry of 21 nearby type II Cepheids in the near-infrared J, H, and K s passbands. We use this photometry, together with the Third Gaia Early Data Release parallaxes, to determine for the first time period-luminosity relations (PLRs) for type II Cepheids from field representatives of these old pulsating stars in the near-infrared regime. We found PLRs to be very narrow for BL Herculis stars, which makes them candidates for precision distance indicators. We then use archival photometry and the most accurate distance obtained from eclipsing binaries to recalibrate PLRs for type II Cepheids in the Large Magellanic Cloud (LMC). Slopes of our PLRs in the Milky Way and in the LMC differ by slightly more than 2σ and are in a good agreement with previous studies of the LMC, Galactic bulge, and Galactic globular cluster type II Cepheids samples. We use PLRs of Milky Way type II Cepheids to measure the distance to the LMC, and we obtain a distance modulus of 18.540 ± 0.026(stat.) ± 0.034(syst.) mag in the W JK Wesenheit index. We also investigate the metallicity effect within our Milky Way sample, and we find a rather significant value of about -0.2 mag dex-1 in each band meaning that more metal-rich type II Cepheids are intrinsically brighter than their more metal-poor counterparts, in agreement with the value obtained from type II Cepheids in Galactic globular clusters. The main source of systematic error on our Milky Way PLRs calibration, and the LMC distance, is the current uncertainty of the Gaia parallax zero-point.
- ItemReflectivity of Venus’s Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives([Bristol] : IOP Publishing, 2022) Lee, Yeon Joo; García Muñoz, Antonio; Yamazaki, Atsushi; Quémerais, Eric; Mottola, Stefano; Hellmich, Stephan; Granzer, Thomas; Bergond, Gilles; Roth, Martin; Gallego-Cano, Eulalia; Chaufray, Jean-Yves; Robidel, Rozenn; Murakami, Go; Masunaga, Kei; Kaplan, Murat; Erece, Orhan; Hueso, Ricardo; Kabáth, Petr; Špoková, Magdaléna; Sánchez-Lavega, Agustín; Kim, Myung-Jin; Mangano, Valeria; Jessup, Kandis-Lea; Widemann, Thomas; Sugiyama, Ko-ichiro; Watanabe, Shigeto; Yamada, Manabu; Satoh, Takehiko; Nakamura, Masato; Imai, Masataka; Cabrera, JuanWe performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns.