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Since its launch, the Alpha Magnetic Spectrometer - 02 (AMS-02) has delivered outstanding quality measurements of the spectra of cosmic-ray (CR) species, $\bar{p}$, $e^{\pm}$, and nuclei, $_1$H-$_8$O, $_{10}$Ne, $_{12}$Mg, $_{14}$Si, which resulted in a number of breakthroughs. One of the latest long awaited surprises is the spectrum of $_{26}$Fe just published by AMS-02. Because of the large fragmentation cross section and large ionization energy losses, most of CR iron at low energies is local, and may harbor some features associated with relatively recent supernova (SN) activity in the solar neighborhood. Our analysis of new iron spectrum together with Voyager 1 and ACE-CRIS data reveals an unexpected bump in the iron spectrum and in the Fe/He, Fe/O, and Fe/Si ratios at 1-2 GV, while a similar feature in the spectra of He, O, Si, and in their ratios is absent, hinting at a local source of low-energy CRs. The found excess fits well with recent discoveries of radioactive $^{60}$Fe deposits in terrestrial and lunar samples, and in CRs. We provide an updated local interstellar spectrum (LIS) of iron in the energy range from 1 MeV nucleon$^{-1}$ to $\sim$10 TeV nucleon$^{-1}$. Our calculations employ the GalProp-HelMod framework that is proved to be a reliable tool in deriving the LIS of CR $\bar{p}$, $e^{-}$, and nuclei $Z\le28$., 12 pages, 9 figures, 5 tables; Accepted for publication in the Astrophysical Journal. arXiv admin note: text overlap with arXiv:2006.01337

Located in the Large Magellanic cloud and mostly irradiated by a massive-star cluster R$\,$136, 30 Doradus is an ideal target to test the leading theory of the grain alignment and rotational disruption by RAdiative Torques (RATs). Here, we use publicly available polarized thermal dust emission observations of 30 Doradus at 89, 154, and 214$\,\mu$m using SOFIA/HAWC+. We analyse the variation of the dust polarization degree ($p$) with the total emission intensity ($I$), the dust temperature ($T_{\rm d}$), and the gas column density ($N_{\rm H}$) constructed from ${\it Herschel}$ data. The 30 Doradus complex is divided into two main regions relative to R$\,$136, namely North and South. In the North, we find that the polarization degree first decreases and then increases before decreasing again when the dust temperature increases toward the irradiating cluster R$\,$136. The first depolarization likely arises from the decrease of grain alignment efficiency toward the dense medium due to the attenuation of the interstellar radiation field and the increase of the gas density. The second trend (the increase of $p$ with $T_{\rm d}$) is consistent with the RAT alignment theory. The final trend (the decrease of $p$ with $T_{\rm d}$) is consistent with the RAT alignment theory only when the grain rotational disruption by RATs is taken into account. In the South, we find that the polarization degree is nearly independent of the dust temperature, while the grain alignment efficiency is higher around the peak of the gas column density and decreases toward the radiation source. The latter feature is also consistent with the prediction of the rotational disruption by RATs., Comment: 19 pages, 13 figures, 1 table, accepted to ApJ

We present SOFIA/FIFI-LS observations of the [CII] 158${\mu}$m cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H I data to compare [CII] emission to dust properties, star formation rate (SFR), H$_2$, and HI at 560pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute $73\%$ of the [CII] luminosity to arms, and $19\%$ and $8\%$ to the center and interarm region, respectively. [CII]/TIR, [CII]/CO, and [CII]/PAH radial profiles are largely constant, but rise at large radii ($\gtrsim$8kpc) and drop in the center ("[CII] deficit"). This increase at large radii and the observed decline with the 70${\mu}$m/100${\mu}$m dust color are likely driven by radiation field hardness. We find a near proportional [CII]-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. [CII] also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of [CII] as an H$_2$ and SFR tracer in such regimes. Finally, based on the observed [CII] and CO radial profiles and different models, we find ${\alpha}_{CO}$ to increase with radius, in line with the observed metallicity gradient. The low ${\alpha}_{CO}$ (galaxy average $\lesssim2\,M_{sun}\,pc^{-2}\,(K\,km\,s^{-1})^{-1}$) and low [CII]/CO ratios ($\sim$400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way., Comment: 12 pages, 6 Figures, published in ApJ

We present an analysis of the 0.95-14.5 micron spectral energy distributions of nine field ultracool dwarfs with spectral types ranging from L1 to T4.5. Effective temperatures, gravities, and condensate cloud sedimentation efficiencies are derived by comparing the data to synthetic spectra computed from atmospheric models that self-consistently include the formation of condensate clouds. Derived effective temperatures decrease steadily through the L1 to T4.5 spectral types and we confirm that the effective temperatures of ultracool dwarfs at the L/T transition are nearly constant, decreasing by only ~200 K from spectral types L7.5 to T4.5. The two objects in our sample with very red J-Ks colors are best fitted with synthetic spectra that have thick clouds which hints at a possible correlation between the near-infrared colors of L dwarfs and the condensate cloud properties. The fits to the two T dwarfs in our sample (T2 and T4.5) also suggest that the clouds become thinner in this spectral class, in agreement with previous studies. Restricting the fits to narrower wavelength ranges (i.e., individual photometric bands) almost always yields excellent agreement between the data and models. Limitations in our knowledge of the opacities of key absorbers such as FeH, VO, and CH4 at certain wavelengths remain obvious, however. The effective temperatures obtained by fitting the narrower wavelength ranges can show a large scatter compared to the values derived by fitting the full spectral energy distributions; deviations are typically ~200 K and in the worst cases, up to 700 K.

We investigate the quantity and composition of unburned material in the outer layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw. Pristine matter from a white dwarf progenitor is expected to be a mixture of oxygen and carbon in approximately equal abundance. Using near-infrared (NIR, 0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is severely depleted with low upper limits in the outer third of the ejected mass. Strong features from the OI line at rest wavelength = 0.7773 microns are observed through a wide range of expansion velocities approx. 9,000 - 18,000 km/s. This large velocity domain corresponds to a physical region of the supernova with a large radial depth. We show that the ionization of C and O will be substantially the same in this region. CI lines in the NIR are expected to be 7-50 times stronger than those from OI but there is only marginal evidence of CI in the spectra and none of CII. We deduce that for these three normal SNe Ia, oxygen is more abundant than carbon by factors of 100 - 1,000. MgII is also detected in a velocity range similar to that of OI. The presence of O and Mg combined with the absence of C indicates that for these SNe Ia, nuclear burning has reached all but the extreme outer layers; any unburned material must have expansion velocities greater than 18,000 km/s. This result favors deflagration to detonation transition (DD) models over pure deflagration models for SNe Ia., Comment: accepted for publication in ApJ

V1647 Ori is a low-mass star in the L1630 star-forming region that underwent an outburst in late 2003 and early 2004. We present postoutburst infrared spectra obtained with NIRSPEC (Keck II) and SpeX (IRTF) and compare these to spectra taken during the outburst. The results show that the temperature of the hot CO formed in the inner part of the disk has declined by ~800 K, while the water and CO ice and low-J CO gas features remained unchanged, consistent with previous assertions that the latter, low-temperature features arise in the foreground cloud. The P Cygni profiles of the Paschen series that were present in the outburst spectra taken in 2004 March disappeared by late 2004. The equivalent width of the helium absorption line at 1.0830 μm decreased from 8.9 to 3.9 A between 2004 March and November, evidence that the hot, fast wind has decreased substantially. We discuss the implications for categorizing V1647 Ori among the known classes of outbursting young stars.

(Abridged) We present high spatial resolution ultraviolet and optical spectroscopy, obtained using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, of nuclear structures within four `warm' Ultraluminous Infrared Galaxies (ULIRGs). We find an AGN in at least three, and probably all four of our sample, hosted in a compact, optically luminous `knot'. In three cases these knots were previously identified as a putative AGN nucleus from multiband optical imaging. Three of the sample also harbor a starburst in one or more knots, suggesting that the optically luminous knots seen in local ULIRGs are the most likely sites of the dust-shrouded starburst and AGN activity that power the infrared emission. The four AGN have a diverse range of properties; two are classical narrow line AGN, one shows both broad and narrow lines and evidence for lines of sight from the narrow through to the broad line regions, and one is plausibly a FeLoBAL AGN. The probable presence in one object of an FeLoBAL AGN, which are extremely rare in the QSO population, supports the idea that LoBAL AGN may be youthful systems shrouded in gas and dust rather than AGN viewed along a certain line of sight. The three starbursts for which detailed constraints are possible show a smaller range in properties; all three bursts are young with two having ages of ~4Myr and the third having an age of 20Myr, suggesting that ULIRGs undergo several bursts of star formation during their lifetimes. None of the starbursts show evidence for Initial Mass Function slopes steeper than about 3.3. The metallicities of the knots for which metallicities can be derived are all at least 1.5 times the Solar value. The properties of one further starburst knot are consistent with it being the forming core of an elliptical galaxy.

We present 0.8-5.2 micron spectroscopy of the compact source at the base of a variable nebula (McNeil's Nebula Object) in the Lynds 1630 dark cloud that went into outburst in late 2003. The spectrum of this object reveals an extremely red continuum, CO bands at 2.3-2.5 microns in emission, a deep 3.0 micron ice absorption feature, and a solid state CO absorption feature at 4.7 microns. In addition, emission lines of H, Ca II, Mg I, and Na I are present. The Paschen lines exhibit P Cygni profiles, as do two lines of He I, although the emission features are very weak in the latter. The Brackett lines, however, are seen to be purely in emission. The P Cygni profiles clearly indicate that mass outflow is occurring in a wind with a velocity of ~400 km/s. The H line ratios do not yield consistent estimates of the reddening, nor do they agree with the extinction estimated from the ice feature (A_V ~ 11). We propose that these lines are optically thick and are produced in a dense, ionized wind. The near-infrared spectrum does not appear similar to any known FUor or EXor object. However, all evidence suggests that McNeil's Nebula Object is a heavily-embedded low-mass Class I protostar, surrounded by a disk, whose brightening is due to a recent accretion event., 11 pages, 2 ps figures, accepted for publication in ApJ Letters

We report near infrared (NIR) spectroscopic observations of twelve ``Branch-normal'' Type Ia supernovae (SNe Ia) which cover the wavelength region from 0.8-2.5 microns. Our sample more than doubles the number of SNe Ia with published NIR spectra within three weeks of maximum light. The epochs of observation range from thirteen days before maximum light to eighteen days after maximum light. A detailed model for a Type Ia supernovae is used to identify spectral features. The Doppler shifts of lines are measured to obtain the velocity and, thus, the radial distribution of elements. The NIR is an extremely useful tool to probe the chemical structure in the layers of SNe Ia ejecta. This wavelength region is optimal for examining certain products of the SNe Ia explosion that may be blended or obscured in other spectral regions. We identify spectral features from MgII, CaII, SiII, FeII, CoII, NiII and possibly MnII. We find no indications for hydrogen, helium or carbon in the spectra. The spectral features reveal important clues about the physical characteristics of SNe Ia. We use the features to derive upper limits for the amount of unburned matter, to identify the transition regions from explosive carbon to oxygen burning and from partial to complete silicon burning, and to estimate the level of mixing during and after the explosion., Comment: 44 pages, 7 figures, 3 tables, accepted by ApJ

We present a NASA-DLR SOFIA-Echelon Cross Echelle Spectrograph (EXES) and NASA Infrared Telescope Facility-Texas Echelon Cross Echelle Spectrograph (TEXES) mid-IR R ≃ 50,000 spectral study of forbidden Fe II transitions in the early-type M supergiants, Betelgeuse (α Ori: M2 Iab) and Antares (α Sco: M1 Iab + B3 V). With EXES, we spectrally resolve the ground term [Fe II] 25.99 μm ( a 6DJ= 7/2-9/2: Eup = 540 K) emission from Betelgeuse. We find a small centroid blueshift of 1.9 ± 0.4 km s-1 that is a significant fraction (20%) of the current epoch wind speed, with a FWHM of 14.3 ± 0.1 km s-1. The TEXES observations of [Fe II] 17.94 μm (a 4FJ= - 7/2 9/2: Eup = 3400 K) show a broader FWHM of 19.1 ± 0.2 km s-1, consistent with previous observations, and a small redshift of 1.6 ± 0.6 km s-1 with respect to the adopted stellar center-ofmass velocity of VCoM = 20.9 ± 0.3 km s-1. To produce [Fe II] 25.99 μm blueshifts of 20% wind speed requires that the emission arises closer to the star than existing thermal models for α Ori's circumstellar envelope predict. This implies a more rapid wind cooling to below 500 K within 10R∗ (q∗ = 44 mas, dist = 200 pc) of the star, where the wind has also reached a significant fraction of the maximum wind speed. The line width is consistent with the turbulence in the outflow being close to the hydrogen sound speed. EXES observations of [Fe II] 22.90 μm ( a 4DJ= 5/2-7/2: Eup = 11,700 K) reveal no emission from either star. These findings confirm the dominance of cool plasma in the mixed region where hot chromospheric plasma emits copiously in the UV, and they also constrain the wind heating produced by the poorly understood mechanisms that drive stellar outflows from these low variability and weak-dust signature stars.

Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of observed emission line strengths from Wolf-Rayet (WR) stars, we construct evolutionary synthesis models for young starbursts. We explicitly distinguish between the various WR subtypes (WN, WC, WO), and we treat O and Of stars separately. We provide detailed predictions of UV and optical emission line strengths for both the WR stellar lines and the major nebular hydrogen and helium emission lines, as a function of several input parameters related to the starburst episode. We also derive the theoretical frequency of WR-rich starbursts. We then discuss: nebular HeII 4686 emission, the contribution of WR stars to broad Balmer line emission, techniques used to derive the WR and O star content from integrated spectra, and explore the implications of the formation of WR stars through mass transfer in close binary systems in instantaneous bursts. The observational features predicted by our models allow a detailed quantitative determination of the massive star population in a starburst region (particularly in so-called "WR galaxies") from its integrated spectrum and provide a means of deriving the burst properties (e.g., duration, age) and the parameters of the initial mass function of young starbursts. (Abridged abstract), Accepted by ApJ Supplements. LaTeX using aasmp4, psfigs macros. 49 pages including 23 figures. Paper (full, or text/figures separated) and detailed model results available at http://www.stsci.edu/ftp/science/starburst/sv97.html