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1. The ROSAT Raster survey in the north ecliptic pole field: X-ray catalogue and optical identifications

   https://doi.org/10.1051/0004-6361/202039476  

   Hasinger, G. ; Freyberg, M. ; Hu, E. M. ; Waters, C. Z. ; Capak, P. ; Moneti, A. ; McCracken, H. J. ( January 2021 , Astronomy & Astrophysics)

   null (Ed.)

   The north ecliptic pole (NEP) is an important region for extragalactic surveys. Deep and wide contiguous surveys are being performed by several space observatories, most currently with the eROSITA telescope. Several more are planned for the near future. We analyse all the ROSAT pointed and survey observations in a region of 40 deg 2 around the NEP, restricting the ROSAT field of view to the inner 30′ radius. We obtain an X-ray catalogue of 805 sources with 0.5−2 keV fluxes > 2.9 × 10 −15 erg cm −2 s −1 , about a factor of three deeper than the ROSAT All-Sky Survey in this field. The sensitivity and angular resolution of our data are comparable to the eROSITA All-Sky Survey expectations. The 50% position error radius of the sample of X-ray sources is ∼10″. We use HEROES optical and near-infrared imaging photometry from the Subaru and Canada/France/Hawaii telescopes together with GALEX, SDSS, Pan-STARRS, and WISE catalogues, as well as images from a new deep and wide Spitzer survey in the field to statistically identify the X-ray sources and to calculate photometric redshifts for the candidate counterparts. In particular, we utilize mid-infrared (mid-IR) colours to identify active galactic nucleus (AGN) X-ray counterparts. Despite the relatively large error circles and often faint counterparts, together with confusion issues and systematic errors, we obtain a rather reliable catalogue of 766 high-quality optical counterparts, corresponding redshifts and optical classifications. The quality of the dataset is sufficient to look at ensemble properties of X-ray source classes. In particular we find a new population of luminous absorbed X-ray AGN at large redshifts, identified through their mid-IR colours. This populous group of AGN was not recognized in previous X-ray surveys, but could be identified in our work due to the unique combination of survey solid angle, X-ray sensitivity, and quality of the multi-wavelength photometry. We also use the WISE and Spitzer photometry to identify a sample of 185 AGN selected purely through their mid-IR colours, most of which are not detected by ROSAT. Their redshifts and upper limits to X-ray luminosity and X-ray–to–optical flux ratios are even higher than for the new class of X-ray selected luminous type 2 AGN (AGN2); they are probably a natural extension of this sample. This unique dataset is important as a reference sample for future deep surveys in the NEP region, in particular for eROSITA and also for Euclid and SPHEREX. We predict that most of the absorbed distant AGN should be readily picked up by eROSITA, but they require sensitive mid-IR imaging to be recognized as optical counterparts. 

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2. C60 cation as the carrier of the λ 9577 Å and λ 9632 Å diffuse interstellar bands: further support from the VLT/X-Shooter spectra

   https://doi.org/10.1093/mnras/stab3296  

   Nie, T. P. ; Xiang, F. Y. ; Li, Aigen ( November 2021 , Monthly Notices of the Royal Astronomical Society)

   Ever since they were first detected over 100 yr ago, the mysterious diffuse interstellar bands (DIBs), a set of several hundred broad absorption features seen against distant stars in the optical and near-infrared wavelength range, largely remain unidentified. The close match, both in wavelengths and in relative strengths, recently found between the experimental absorption spectra of gas-phase buckminsterfullerene ions (C$_{60}^{+}$) and four DIBs at $\lambda 9632\, {\rm \mathring{\rm A}}$, $\lambda 9577\, {\rm \mathring{\rm A}}$, $\lambda 9428\, {\rm \mathring{\rm A}}$ and $\lambda 9365\, {\rm \mathring{\rm A}}$ (and, to a lesser degree, a weaker DIB at $\lambda 9348\, {\rm \mathring{\rm A}}$) suggests that C$_{60}^{+}$ is a promising carrier for these DIBs. However, arguments against the C$_{60}^{+}$ identification remain and are mostly concerned with the large variation in the intensity ratios of the $\lambda 9632\, {\rm \mathring{\rm A}}$ and $\lambda 9577\, {\rm \mathring{\rm A}}$ DIBs. In this work, we search for these DIBs in the X-shooter archival data of the European Southern Observatory’s Very Large Telescope, and we identify the $\lambda 9632\, {\rm \mathring{\rm A}}$, $\lambda 9577\, {\rm \mathring{\rm A}}$, $\lambda 9428\, {\rm \mathring{\rm A}}$ and $\lambda 9365\, {\rm \mathring{\rm A}}$ DIBs in a sample of 25 stars. While the $\lambda 9428\, {\rm \mathring{\rm A}}$ and $\lambda 9365\, {\rm \mathring{\rm A}}$ DIBs are too noisy to allow any reliable analysis, the $\lambda 9632\, {\rm \mathring{\rm A}}$ and $\lambda 9577\, {\rm \mathring{\rm A}}$ DIBs are unambiguously detected and, after correcting for telluric water vapour absorption, their correlation can be used to probe their origin. To this end, we select a subsample of nine hot, O- or B0-type stars of which the stellar Mg ii contamination to the $\lambda 9632\, {\rm \mathring{\rm A}}$ DIB is negligibly small. We find that their equivalent widths, after being normalized by reddening to eliminate their common correlation with the density of interstellar clouds, exhibit a tight, positive correlation, supporting C$_{60}^{+}$ as the carrier of the $\lambda 9632\, {\rm \mathring{\rm A}}$ and $\lambda 9577\, {\rm \mathring{\rm A}}$ DIBs.

    

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3. The CARMENES search for exoplanets around M dwarfs: Wolf 1069 b: Earth-mass planet in the habitable zone of a nearby, very low-mass star

   https://doi.org/10.1051/0004-6361/202245322  

   Kossakowski, D. ; Kürster, M. ; Trifonov, T. ; Henning, Th. ; Kemmer, J. ; Caballero, J. A. ; Burn, R. ; Sabotta, S. ; Crouse, J. S. ; Fauchez, T. J. ; et al ( February 2023 , Astronomy & Astrophysics)

   We present the discovery of an Earth-mass planet (M_bsini= 1.26 ± 0.21M_⊕) on a 15.6 d orbit of a relatively nearby (d ~9.6 pc) and low-mass (0.167 ± 0.011M_⊙) M5.0 V star, Wolf 1069. Sitting at a separation of 0.0672 ± 0.0014 au away from the host star puts Wolf 1069 b in the habitable zone (HZ), receiving an incident flux ofS= 0.652 ± 0.029S_⊕. The planetary signal was detected using telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph, amounting to a total of 262 spectroscopic observations covering almost four years. There are additional long-period signals in the RVs, one of which we attribute to the stellar rotation period. This is possible thanks to our photometric analysis including new, well-sampled monitoring campaigns undergone with the OSN and TJO facilities that supplement archival photometry (i.e., from MEarth and SuperWASP), and this yielded an updated rotational period range ofP_rot= 150–170 d, with a likely value at 169.3_−3.6^+3.7. The stellar activity indicators provided by the CARMENES spectra likewise demonstrate evidence for the slow rotation period, though not as accurately due to possible factors such as signal aliasing or spot evolution. Our detectability limits indicate that additional planets more massive than one Earth mass with orbital periods of less than 10 days can be ruled out, suggesting that perhaps Wolf 1069 b had a violent formation history. This planet is also the sixth closest Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ 1061 d, Teegarden’s Star c, and GJ 1002 b and c. Despite not transiting, Wolf 1069 b is nonetheless a very promising target for future three-dimensional climate models to investigate various habitability cases as well as for sub-m s⁻¹RV campaigns to search for potential inner sub-Earth-mass planets in order to test planet formation theories.

    

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4. Radiometric Temperature Determination in Nongray Bridgmanite: Applications to Melting Curve and Post‐Perovskite Transition Boundary in the Lower Mantle

   https://doi.org/10.1029/2021JB021723  

   Lobanov, Sergey S. ; Speziale, Sergio ; Lin, Jung‐Fu ; Schifferle, Lukas ; Schreiber, Anja ( May 2021 , Journal of Geophysical Research: Solid Earth)

   Experiments in laser‐heated diamond anvil cells (LH DACs) are conducted to assess phase diagrams of planetary materials at high pressure‐temperature (P‐T) conditions; thus, reliable determination of temperature in LH DAC experiments is essential. Radiometric temperature determination in LH DACs relies on the assumption of sample's wavelength‐independent optical properties (graybody assumption), which is not justified for major lower mantle materials. The result is that experimental phase diagrams contain systematic unconstrained errors. Here we estimate the systematic error in radiometric temperature of nongray polycrystalline bridgmanite (Bgm; Mg_0.96Fe²⁺_0.036Fe³⁺_0.014Si_0.99O₃) in a LH DAC by modeling emission and absorption of thermal radiation in a sample with experimentally‐constrained optical properties. A comparison to experimental data validates the models and reveals that thermal spectra measured in LH DAC experiments record the interaction of radiation with the hot nongray sample. The graybody assumption in the experiments on translucent Bgm (light extinction coefficient,k < ∼250 cm^‐1at 500–900 nm) yields temperatures ∼5% higher than the maximum temperature in the sample heated to ∼1900 K. In contrast, the graybody temperature of dark Bgm (k > ∼1500 cm⁻¹), such as that produced upon melt quenching in LH DACs, underestimates the maximum temperature by ∼10%. Our experimental results pose quantitative constraints on the effect of nongray optical properties on the uncertainty of radiometric temperature determination in Bgm in the LH DACs. Evaluating nongray temperature in the future would enable a revision of the Bgm to post‐perovskite phase transition and the high‐pressure melting curve of Bgm.

    

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5. A Luminous Red Supergiant and Dusty Long-period Variable Progenitor for SN 2023ixf

   https://doi.org/10.3847/2041-8213/ace618  

   Jencson, Jacob E. ; Pearson, Jeniveve ; Beasor, Emma R. ; Lau, Ryan M. ; Andrews, Jennifer E. ; Bostroem, K. Azalee ; Dong 董, Yize 一泽 ; Engesser, Michael ; Gomez, Sebastian ; Guolo, Muryel ; et al ( July 2023 , The Astrophysical Journal Letters)

   We analyze pre-explosion near- and mid-infrared (IR) imaging of the site of SN 2023ixf in the nearby spiral galaxy M101 and characterize the candidate progenitor star. The star displays compelling evidence of variability with a possible period of ≈1000 days and an amplitude of Δm≈ 0.6 mag in extensive monitoring with the Spitzer Space Telescope since 2004, likely indicative of radial pulsations. Variability consistent with this period is also seen in the near-IRJandK_sbands between 2010 and 2023, up to just 10 days before the explosion. Beyond the periodic variability, we do not find evidence for any IR-bright pre-supernova outbursts in this time period. The IR brightness ($M_{K_s}=-10.7$mag) and color (J−K_s= 1.6 mag) of the star suggest a luminous and dusty red supergiant. Modeling of the phase-averaged spectral energy distribution (SED) yields constraints on the stellar temperature ($T_{\mathrm{eff}}={3500}_{-1400}^{+800}$K) and luminosity ($\log L/L_{\odot }=5.1\pm 0.2$). This places the candidate among the most luminous Type II supernova progenitors with direct imaging constraints, with the caveat that many of these rely only on optical measurements. Comparison with stellar evolution models gives an initial mass ofM_init= 17 ± 4M_⊙. We estimate the pre-supernova mass-loss rate of the star between 3 and 19 yr before explosion from the SED modeling at$\dot{M}\approx 3\times {10}^{-5}$to 3 × 10⁻⁴M_⊙yr⁻¹for an assumed wind velocity ofv_w= 10 km s⁻¹, perhaps pointing to enhanced mass loss in a pulsation-driven wind.

    

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