adsabs/FOCAL huggingface dataset:
GX 301-2 is an HMXB consisting of a highly magnetized (B ∼ 4 × 1012 G, or even larger Doroshenko et al. 2010) pulsar and a B-type hyper-giant star Wray 977 (Vidal 1973; Kaper et al. 1995; Staubert et al. 2019). According to modelling of high-resolution optical spectra, Wray 977 has a mass of 43 ± 10 $\, \mathrm{M}_{\odot }$, a radius of 62 R⊙, and looses mass through powerful stellar winds at a rate of $\sim \! 10^{-5}\, \mathrm{M}_\odot \, {\rm yr}^{-1}$ with terminal velocity of 300 $\rm km\, s^{-1}$ (Kaper, van der Meer & Najarro 2006). The system is highly eccentric (e ∼ 0.46), with an orbital period of ∼41.5 d, and exhibits strong variation of the X-ray flux with orbital phase (Koh et al. 1997; Doroshenko et al. 2010). In particular, periodic outbursts at the orbital phase ∼1.4 d before the periastron passage (Sato et al. 1986), and a fainter one near the apastron passage are observed (Pravdo et al. 1995). The broad-band X-ray spectrum is orbital phase-dependent and can be approximately described as a power law with a high-energy cutoff and a cyclotron resonant scattering feature around 40 keV (Kreykenbohm et al. 2004; Mukherjee & Paul 2004; La Barbera et al. 2005; Doroshenko et al. 2010; Suchy et al. 2012; Islam & Paul 2014; Fürst et al. 2018; Nabizadeh et al. 2019). During the periastron flares, the source exhibits strong variability with an amplitude of up to a factor of 25, reaching a few hundreds mCrab in the energy band of 2–10 keV (e.g. Rothschild & Soong 1987; Pravdo et al. 1995). The flares are accompanied by the variability of the equivalent hydrogen column density ($\rm \mathit{ N}_{\rm H}$) and of the fluorescent iron lines, which is believed to be associated with clumpiness of the stellar wind, launched from the donor star (Mukherjee & Paul 2004). We note the clumpiness in this paper refers to any inhomogeneities in the stellar wind/stream, which are higher density regions, regardless of its specific formation mechanisms. On the other hand, Fürst et al. (2011) reported a long XMM–Newton observation in GX 301-2 around its periastron, which also exhibits systematic variations of the flux and $\rm \mathit{ N}_{H}$ at a time-scale of a few kiloseconds. Several wind accretion models, consisting of stellar winds and a gas stream, were proposed to explain the observed flares (e.g. Haberl 1991; Leahy 1991; Leahy & Kostka 2008; Mönkkönen et al. 2020).
Citation: Mukherjee & Paul 2004
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Citation: Mukherjee & Paul 2004
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Admittedly, although the prediction success rate of SPM3 is greatly improved compared with the previous SPM2 model, its improvements in the shock TT prediction are limited. Many factors could potentially cause this. On one hand, the sample events used in this study are CMEs from Solar Cycle 23 when SOHO was the only spacecraft tracking their movements in the sky-plane. The CME speed derived in this way is the projected speed, which does not represent the propagation speed of the CME along the Sun–Earth direction. Large uncertainties in VCME restrict further improvements to the TT prediction of the shock. Possible solutions to this restriction could include adopting the CME’s radial speed, which is derived from models (such as cone models) based on single spacecraft observations (Jang et al. 2014). Another solution involves estimating the initial geometry and three-dimensional (3D) speeds of CMEs based on observations from multiple spacecraft (STEREO, SOHO; Kilpua et al. 2012; Gopalswamy et al. 2013; Lee et al. 2013). On the other hand, the input parameters used in this study were obtained when the disturbances propagated near the Sun. Therefore, the lead time of SPM3's prediction is very long, nearly the whole TT of the disturbance from the Sun to Earth, as the model is analytic and thus requires no running time. Models based on heliospheric image data (STEREO HIs and SMEI) can provide more accurate predictions for arrival times but with shorter lead times (Colaninno et al. 2013; Mishra & Srivastava 2013; Möstl et al. 2014). For example, Webb (2013) applied the Tapping–Howard model (Tapping & Howard 2009) to predict the arrival time at Earth of the 2011 February 15 CME event based on HI and/or SMEI observations, and the corresponding prediction accuracy could be within an hour. However, the prediction’s lead time was only several hours. Kilometric Type II radio burst emission can also be used to track shock dynamics in the inner heliosphere and provide shock arrive time predictions (Corona-Romero et al. 2013; Xie et al. 2013). Further prediction models considering these factors should be developed based on the events of Solar Cycle 24. This is the next goal of our research.
Citation: Jang et al. 2014
Citation function: Compare/Contrast
Line driven winds are not expected to be smooth flows, but show strong density perturbations or “clumps” (Owocki et al. 1988; Feldmeier et al. 1997; Puls et al. 2006, 2008; Oskinova et al. 2012; Sundqvist & Owocki 2013). In X-ray binaries, thedensity contrast could even be further enhanced by the interaction between the wind and the strong X-rays from the compact object (Blondin 1994; Blondin & Woo 1995; Manousakis & Walter 2011, 2015, and references therein). For Vela X-1 and Cyg X-1 it has been estimated that more than 90% of the wind mass is contained in less than 10% of the wind volume (Sako et al. 1999; Rahoui et al. 2011). When the line of sight to the compact object passes through one of these clumps, X-rays are absorbed by the moderately ionized material in the clump, leading to a so-called dipping event. This is also observed for other sources (Hemphill et al. 2014; Grinberg et al. 2017). During the hard state of Cyg X-1, such short-term dipping events are observed predominantly during the upper conjunction of the black hole, i.e., when the line of sight passes through the densest region of the stellar wind and is most likely to pass through a clump (Li & Clark 1974; Mason et al. 1974; Parsignault et al. 1976; Pravdo et al. 1980; Remillard & Canizares 1984; Kitamoto et al. 1984; Bałucińska-Church et al. 2000; Feng & Cui 2002; Poutanen et al. 2008; Hanke et al. 2009; Miškovičová et al. 2016; Grinberg et al. 2015). The precise structure of the clumps, i.e., their density and ionization structure, is unknown. Most recent 2D simulations of such a stellar wind show a very complex evolution of velocity and density structures with the formation of characteristic small-scale clumps of various shapes embedded in areas with lower density (Sundqvist et al. 2018). Sundqvist et al. (2018) have found a typical clump mass of 1017 g and an average clump size of 1% of the stellar radius at a distance of two stellar radii. These results qualitatively confirm earlier theoretical models (e.g., Oskinova et al. 2012; Sundqvist & Owocki 2013) and observations (e.g., Grinberg et al. 2015). See also the review paper by Martínez-Núñez et al. (2017).
Citation: Grinberg et al. 2017
Citation function: Similarities
Ricci et al. (2017c, hereafter R17c) recently reported on a study of the relationship between obscuration and accretion rate in a large, relatively unbiased, and complete sample of local AGNs. Specifically, they investigated 836 AGNs with a median redshift of 〈z〉 = 0.037 selected by the hard X-ray (14–195 keV) Swift Burst Alert Telescope (BAT; Gehrels et al. 2004; Barthelmy et al. 2005; Krimm et al. 2013) all-sky survey (Baumgartner et al. 2013; Koss et al. 2017; Oh et al. 2018), which is sensitive to sources with column densities up to NH ≈ 1024 cm−2.  Approximately one-half of the sources had robust measurements of column densities, intrinsic X-ray luminosities, and black hole masses, from which R17c was able to show that while unobscured AGNs are seen with Eddington fractions up to the Eddington limit, very few local, obscured AGNs are found with Eddington fractions above approximately 10%. This strengthened earlier results based on smaller samples (e.g., Fabian et al. 2009) and was interpreted as evidence for radiation-pressure-driven AGN feedback (e.g., King 2003; Murray et al. 2005) clearing the immediate BH environment of dusty gas (e.g., Fabian et al. 2006, 2008). For dusty gas (neutral or partially ionized), the effective cross section between matter and radiation (σdust) becomes larger than that between electrons and radiation for ionized gas (σT, for Thompson scattering), due to absorption of radiation by dust. This is given by the Eddington ratio for ionized gas,
1





where Lbol is the bolometric luminosity, LEdd is the Eddington luminosity with MBH the BH mass, and mp is the proton mass. For dusty gas, we use σdust instead of σT in Equation (1), where fEdd is redefined as the effective Eddington ratio (fEdd,dust = fEddσdust/σT). AGNs are strong ionizing sources, but they are fully ionized close to their accretion disks (e.g., Osterbrock 1979; Ballantyne et al. 2001), though the greater than parsec-scale environment starts to be composed of dusty gas (e.g., Kishimoto et al. 2011; Minezaki et al. 2019).
Citation: Fabian et al. 2009
Citation function: Similarities
In this context, it must also be noted here that these conclusions are specific to the geometry of the GCS model, which is an idealized geometrical figure that has its limitations and constraints (see Thernisien et al. 2009). Regarding the evolution of the legs, the identification of the two separate legs of the CMEs requires observation at the absolute lower heights. Thus the legs can be identified in the K-Cor FOV, while they are not seen in the COR-1 FOV at the same time, as shown in Figure 1; but it should also be noted that despite the promising FOV of K-Cor, the poor image quality due to the challenges faced from it being a ground-based coronagraph makes it difficult to fit (refer to the discussion in Section 2.2). In this regard, the upcoming ADITYA-L1 mission (Seetha & Megala 2017), with the Visible Emission Line Coronagraph (VELC; FOV: 1.05–3 R
⊙; Banerjee et al. 2017; Prasad et al. 2017) on board, and PROBA-3 (FOV : 1.02–3 R
⊙; Renotte et al. 2014), with the giant Association de Satellites pour l’Imagerie et l’Interferométrie de la Couronne Solaire (ASPIICS; Lamy et al. 2017), will provide much better data and hence will help in arriving at much stronger conclusions on the evolution of CME legs. Having said that, it must also be noted that a true estimation of the volume of CME legs will require the CME to be seen FO, as an FO view will help in identifying the inner edges of the CME and hence the volume of its legs. The studied CMEs in this work are all seen FO in the K-Cor FOV (please see Figure 1). Thus, in future, for a larger statistical study, the appearance of the CME (whether FO or EO) should also be considered in the estimation of the volume of the CME legs. Apart from that, around one-third of CMEs have been reported as having a flux-rope morphology (see Vourlidas et al. 2013), which happens to be the bedrock of the GCS model, thus a study of the three separate sections of the flux-rope model of the CME will help us to have a much better understanding of the validity of self-similar expansion, and thus provide more precise constraints to models that study flux-rope initiation and evolution.
Citation: Prasad et al. 2017
Citation function: Future Work; Future Work; Future Work
Cosmic rays (CRs) represent a crucial ingredient in the dynamical and chemical evolution of interstellar clouds. Interaction of CRs with molecular clouds is accompanied by various processes generating observable radiation signatures, such as ionization of molecular hydrogen (see, e.g., Oka et al. 2005; Dalgarno 2006; Indriolo & McCall 2012) and iron (e.g., Dogiel et al. 1998, 2011; Tatischeff et al. 2012; Yusef-Zadeh et al. 2013; Nobukawa et al. 2015; Krivonos et al. 2017), as well as production of neutral pions whose decay generates gamma-rays in the GeV (e.g., Yang et al. 2014, 2015; Tibaldo et al. 2015) and TeV (e.g., Aharonian et al. 2006; Abramowski et al. 2016; Abdalla et al. 2017) energy ranges. Being a unique source of ionization in dark clouds, where the interstellar radiation cannot penetrate, CRs provide a partial coupling of the gas to magnetic field lines, which could slow down or prevent further contraction of the cloud (e.g., Shu et al. 1987). CRs are fundamental to the beginning of astrochemistry because they promote the formation of 





 ions, which can easily donate a proton to elements such as C and O, and thus eventually form molecules containing elements heavier than H (e.g., Yamamoto 2017). Through the ionization of H2 molecules and the consequent production of secondary electrons, CRs are an important heating source of dark regions (e.g., Goldsmith 2001). Their interaction with H2 can also result in molecular excitation, followed by fluorescence producing a tenuous UV field within dark clouds and dense cores (Cecchi-Pestellini & Aiello 1992; Shen et al. 2004; Ivlev et al. 2015a); this UV field can photodesorb molecules from the icy dust mantles and help to maintain a non-negligible amount of heavy molecules (such as water) in the gas phase (e.g., Caselli et al. 2012). Furthermore, CRs can directly impinge on dust grains and heat up the icy mantles, causing catastrophic explosions of these mantles (Léger et al. 1985; Ivlev et al. 2015b) and activating the chemistry in solids (Shingledecker et al. 2017). Finally, CRs play a fundamental role in the charging of dust grains and the consequent coagulation of dust (Okuzumi 2009; Ivlev et al. 2015a, 2016), which is particularly important for the formation of circumstellar disks (e.g., Zhao et al. 2016) and of planets in more evolved protoplanetary disks (e.g., Testi et al. 2014).
Citation: Yang et al. 2014
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Gomez’s Hamburger (IRAS 18059-3211; hereafter GoHam) is an A star surrounded by a dusty disk. When first studied by Ruiz et al. (1987), it was classified as an evolved object (post-AGB star) on the basis of its spectral type and the presence of dust. However, all recent studies (Bujarrabal et al. 2008, 2009; Wood et al. 2008; De Beck et al. 2010) clearly indicate that it is a young A star surrounded by a protoplanetary disk. The distance to GoHam is not known precisely, but a value d = 250 ± 50 pc is required to satisfy all the existing observational constraints (Wood et al. 2008; Berné et al. 2009; Bujarrabal et al. 2009). We here adopt this value with the uncertainty. GoHam presents intense CO emission; SMA maps of 12CO and 13CO J = 2 − 1 lines very clearly show the Keplerian dynamics of the disk (Bujarrabal et al. 2008, 2009). The lower limit for the disk mass derived from these CO observations is of about 10-2M⊙, while the mass upper limit is estimated to be ~0.3 M⊙  based on dust emission (Bujarrabal et al. 2008; Wood et al. 2008) and assuming an interstellar dust-to-gas mass ratio of 0.01. Overall, GoHam appears to be similar to isolated Herbig stars (Meeus et al. 2001) such as HD 100546 and HD 169142, in a more massive version, but still smaller than the recently discovered disk around CAHA J23056+6016 (Quanz et al. 2010). GoHam is seen almost perfectly edge on, which offers the possibility to study this class of objects from a new and complementary perspective, in particular, with improved constraints on the vertical structure of the disk. Using a radiative transfer model to predict line emission from a Keplerian flaring disk, Bujarrabal et al. (2009) derived a large-scale description of the physical conditions throughout the disk. After subtracting the model that best fit the observations, these authors found a significant residual emission situated about 1.3′′ (330 ± 70 AU) south of the central star, which they identified as a gas condensation, containing a mass between one and few times that of Jupiter. Hence, this source was proposed to be a candidate protoplanet, possibly resulting from a GI collpapse.
Citation: Berné et al. 2009
Citation function: Uses; Uses
Several mechanisms have been proposed to explain the periodicity of methanol masers. van der Walt, Goedhart & Gaylard (2009) and van der Walt (2011) proposed a colliding wind binary (CWB) system for the periodic methanol masers in G9.62+0.20E and other periodic methanol maser sources with similar light curves. Using a more realistic model van den Heever et al. (2019) also showed that the CWB scenario can explain the light curves of the periodic methanol masers in G9.62+0.20E, G22.357+0.066, G37.55+0.20, and G45.473+0.134. Other mechanisms proposed are the pulsational instabilities of very young accreting high-mass stars (Inayoshi et al. 2013), spiral shocks associated with very young binary systems orbiting within a circumbinary disc (Parfenov & Sobolev 2014), periodic accretion in a very young binary system (Araya et al. 2010), and outflows in a binary system (Singh & Deshpande 2012). Maswanganye et al. (2015) evoked an eclipsing binary system involving a high-mass (primary) star and a bloated low-mass (companion) star in explaining the observed periodicity of the methanol masers in G358.460-0.391. While each of the suggested mechanisms may be sufficient for explaining periodicity in individual star-forming regions, the complexity in the nature of massive star-forming environments and the uniqueness of each region, make it difficult to evoke any one of the mechanisms for all cases. In fact, different mechanisms may be responsible for the different observed flare profiles (see van der Walt et al. 2016, for a discussion). However, the fact that it is possible to identify at least two groups of periodic sources (as explained above), each for which the light curves are very similar, suggests that there are some sources for which the underlying mechanism is the same. It is therefore reasonable to argue that there might be other similarities in star-forming regions that host periodic methanol masers with same light curves. In other words, the similarity in light curves might also manifest in other properties of the star-forming regions in addition to the maser emission.
Citation: Parfenov & Sobolev 2014
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Ultra-fast outflows (UFOs) of highly ionised gas observed at sub-parsec scales (Reeves et al. 2003; Tombesi et al. 2012) have been proposed as the likely origin of galaxy-wide outflows, interpreted as the result of the impact of UFOs on the ISM (King & Pounds 2015, and references therein). Furthermore, both models and observations of kiloparsec-scale outflows seem to indicate a UFO-ISM interaction in an energy-conserving regime, whereby the swept-up gas expands adiabatically. So far, the co-existence of a massive molecular outflow with a nuclear UFO has been confirmed in a handful of AGNs with LBol  ∼  1044 − 1046 erg s−1 (Tombesi et al. 2015; Feruglio et al. 2015; Longinotti et al. 2015) and in APM 08279+5255 (Feruglio et al. 2017), which is a gravitationally lensed QSO at z  ∼  4 with an estimated intrinsic LBol of a few times 1047 erg s−1 (Saturni et al. 2018). In all these sources the momentum boost (i.e. the momentum flux of the wind normalised to the AGN radiative momentum output, LBol/c) of the UFO is ∼1, while the momentum rate of the molecular outflow is usually ≫1, in qualitative agreement with the theoretical predictions for an energy-conserving expansion (Faucher-Giguère & Quataert 2012; Costa et al. 2014). However, these results are still limited to a very small sample and suffer from large observational uncertainties, mostly due to the relatively low signal-to-noise ratio of the UFO- or outflow-related features confirmed in spectra, or to the limited spatial resolution of sub-millimetre observations. Recent studies increasing the statistics of sources with detection of molecular outflows have widened the range of measured energetics (e.g. García-Burillo et al. 2014; Veilleux et al. 2017; Feruglio et al. 2017; Brusa et al. 2018; Barcos-Muñoz et al. 2018; Fluetsch et al. 2019). These outflows are consistent with driving mechanisms alternative to the energy-conserving expansion, such as direct radiation pressure onto the host-galaxy ISM (e.g. Ishibashi & Fabian 2014; Ishibashi et al. 2018; Costa et al. 2018).
Citation: Feruglio et al. 2017
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Asymptotic-giant-branch (AGB) stars have a significantly larger size (∼1 au) than their main-sequence (MS) counterparts. They have pulsating atmospheres (Vlemmings et al. 2017; Khouri et al. 2019) and may exhibit variability with long periods ranging from 200 to 1000 days (Mowlavi et al. 2018; Karambelkar et al. 2019). AGB stars are one of the major sites in galaxies that produce metals. Metals can be carried away from the AGB stars by radiation-driven AGB winds when dust forms. The speed of the AGB wind varies from 4 to 20 km s−1 (Höfner & Olofsson 2018), and a companion star may capture the wind with its gravity. In the case that there is an MS star close to an AGB star, a substantial fraction of the mass loss may be accreted onto the MS companion (Chen et al. 2017; Saladino et al. 2018, 2019). As a result, the metallicity of the companion may change. Such early stage low-mass stars become chemically peculiar, and their future evolution will be strongly affected. Carbon-enhanced-metal-poor (CEMP) stars (Beers & Christlieb 2005; Abate et al. 2013, 2015), Barium stars (Bidelman & Keenan 1951; Escorza et al. 2019), CH stars (Keenan 1942; McClure & Woodsworth 1990), and dwarf carbon stars (Dahn et al. 1977; Roulston et al. 2019) are common examples of the chemically peculiar stars. Their existence could be evidence of mass transfer during the previous AGB binary phase. The binarity of CH stars and CEMP stars has been studied (McClure & Woodsworth 1990; Starkenburg et al. 2014; Jorissen et al. 2016), confirming that many of them have companions. A number of recent studies show that the eccentricity of some of the aforementioned chemically peculiar stars may be large (Hansen et al. 2016; Jorissen et al. 2016, 2019; Van der Swaelmen 2017; Oomen et al. 2018), and their orbital periods range from hundreds to thousands of days. The nonzero eccentricity in these close binary stars indicates that some intense interactions that can pump the eccentricity may happen during their AGB binary phases. A strong correlation between a circumstellar disk and binarity has also been established in Galactic RV Tauri stars (Manick et al. 2017). Furthermore, many RV Tauri stars show a lack of refractory elements, which is called “depletion” (Giridhar et al. 1994; Van Winckel et al. 1998). Some researches suggest that the reaccretion of gas from a circumstellar disk around the post-AGB star (Gezer et al. 2019; Oomen et al. 2019) may induce the “depletion.” Besides the “smoking gun” evidence, observations also reveal that dusty circumbinary disks exist in binary systems with evolved stars (Kervella et al. 2015; Hillen et al. 2016; Homan et al. 2017; Ertel et al. 2019). The UV excess of some AGB stars also suggests that there could be accreting MS companions near them (Sahai et al. 2008; Ortiz & Guerrero 2016).
Citation: Saladino et al. 2018
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