Markus Mugrauer

Aims. The secondaries of massive binary systems can be found as runaway stars after being ejected due to the supernova (SN) of the more massive component. We search for such stars inside supernova remnants (SNRs), where a recent SN is guaranteed to have occurred and the runaway star is expected nearby. In this paper, we present the massive runaway star HD 254577 as the pre-SN binary companion to the progenitor of the SN remnant IC 443 and the neutron star (NS) CXOU J61705.3+222127. Methods. We performed spectroscopic observations of the runaway star and specified its atmospheric parameters. We also used archival spectroscopic data on neighboring stars. Together with precise Gaia DR3 astrometry and photometry, we identified the possible birth origin of the runaway star. By isochrone fitting, we likewise determined its progenitor mass. From Gaia DR3 proper motions, we specified the possible explosion sites and calculated the NS velocity. Results. HD 254577 is a hot and evolved star with an effective temperature of 24 000 ± 1000 K (B0.5II) and a surface gravity of log( g [cm/s ² ]) = 2.75 ± 0.25. It is probably a single star with a peculiar 3D velocity of 31.3 _−0.9 ^+1.2 km s ⁻¹ , lying at a heliocentric distance of 1701 ₋₅₄ ⁺⁵⁵ pc. The cometary tail of the NS implies that it is moving away from the same site as the runaway star. From the flight trajectories, we calculated typical NS pulsar velocities of 254 − 539 km s ⁻¹ at a distance of 1.7 kpc for 10 − 20 kyr ages. Together with the blue-shifted interstellar medium lines in its spectrum, HD 254577 must be the pre-SN binary companion to the progenitor of IC 443. By identifying the pre-SN companion and the possible parent cluster, we show that the progenitor zero-age main-sequence mass is high (31 − 64 M _⊙ ), favoring the jet scenario previously proposed. The SNR distance is precisely determined as 1701 ₋₅₄ ⁺⁵⁵ pc. We also discuss the expansion dynamics of the SNR due to the highly off-centered explosion site. Our calculated pre-SN binary parameters might not favor a strongly interacting binary.

We present new radial velocity measurements of 13 selected intermediate mass stars (2–6 M _⊙ ). The measurements were performed between 29 April and 6 September 2024 at the University Observatory Jena using the échelle spectrograph FLECHAS. The radial velocity of eight stars was found to be constant during our spectroscopic monitoring, namely: 17 Dra A, HD 148374, HD 169487 A, 57 Cnc, And, HD 11031, And, and Cas. In contrast, the radial velocity of five stars showed significant variability throughout or spectroscopic observation, namely: 7 CrB A, 7 CrB B, HD 214007, Her, and HD 201433 A. In all these cases, Keplerian orbital solutions were fitted to the observational data and the orbital elements of these spectroscopic binary systems were determined. In addition, we searched for wide companions of our targets using the third data release from ESA's Gaia mission, in order to determine the multiplicity status of these stars and contribute to the census of bright, nearby multiple stars.

The 136 yr long optical light curve of OJ 287 is explained by a binary black hole model where the secondary is in a 12 yr orbit around the primary. Impacts of the secondary on the accretion disk of the primary generate a series of optical flares that follow a quasi-Keplerian relativistic mathematical model. The orientation of the binary in space is determined from the behavior of the primary jet. Here, we ask how the jet of the secondary black hole projects onto the sky plane. Assuming that the jet is initially perpendicular to the disk, and that it is ballistic, we follow its evolution after the Lorentz transformation to the observer’s frame. Since the orbital speed of the secondary is of the order of one-tenth of the speed of light, the result is a change in the jet direction by more than a radian during an orbital cycle. We match the theoretical jet line with the recent 12 μas resolution RadioAstron map of OJ 287 and determine the only free parameter of the problem, the apparent speed of the jet relative to speed of light. It turns out that the Doppler factor of the jet, δ ∼ 5, is much lower than in the primary jet. Besides following a unique shape of the jet path, the secondary jet is also distinguished by a different spectral shape than in the primary jet. The present result on the spectral shape agrees with the huge optical flare of 2021 November 12, also arising from the secondary jet.

In this paper we present the latest results of our ongoing multiplicity survey of (Community) TESS Objects of Interest, using astrometry and photometry from the latest data release of the ESA Gaia mission to detect stellar companions of these stars and to characterize their properties. A total of 92 binary and two hierarchical triple star systems are identified among the 745 target stars whose multiplicity is explored in this study, all at distances of less than 500pc around the Sun. As expected for components of gravitationally bound star systems, the targets and the detected companions are at the same distance and share a common proper motion, as shown by their accurate Gaia astrometry. The companions have masses of about 0.12 to 1.6$M_\odot$. and are most frequently found in the mass range up to 0.6$M_\odot$. The companions have projected separations from the targets between about 110 and 9600au. Their frequency is highest and constant from about 300 to 800au, decreasing at larger projected separations. In addition to main sequence stars, five white dwarf companions are detected in this study, whose true nature is unveiled by their photometric properties.

In this paper, we present the latest results of our ongoing multiplicity survey of (Community) TESS Objects of Interest, using astrometry and photometry from the latest data release of the ESA Gaia mission to detect stellar companions of these stars and to characterize their properties. A total of 92 binary and two hierarchical triple star systems are identified among the 745 target stars whose multiplicity is explored in this study, all at distances of less than 500 pc around the Sun. As expected for components of gravitationally bound star systems, the targets and the detected companions are at the same distance and share a common proper motion, as shown by their accurate Gaia astrometry. The companions have masses of about 0.12 to 1.6 and are most frequently found in the mass range up to 0.6 . The companions have projected separations from the targets between about 110 and 9600 au. Their frequency is highest and constant from about 300 to 800 au, decreasing at larger projected separations. In addition to main sequence stars, five white dwarf companions are detected in this study, whose true nature is unveiled by their photometric properties.

The pulsating variable star Mira (o Ceti) was observed by David Fabricius (Frisia) in 1596 and 1609. We review suggested previous detections (e.g., China, Hipparchos). We analyze all Mira records from Fabricius in their historical context. Fabricius measured the separation of Mira to other stars to ±1.6−1.7′. From his texts, we derive a brightness (slightly brighter than Hamal) of ca. 1.9±0.1 mag and a color index B‐V1.3−1.4 mag (‘like Mars’) for 1596 Aug 3 (Jul.). Mira started to fainten 19 days later and was observed until mid/late Oct. We show why such a red star cannot be followed by the naked eye until ca. 6 mag: For Mira's color at disappearance and altitude from Frisia, the limit is reduced by ca. 1.0 mag. Since Fabricius connected the Mira brightening with the close‐by prograde Jupiter, he re‐detected it only 12 years later, probably shortly before a relatively bright maximum—discoveries are strongly affected by biases. A Mira period of 330.2 days is consistent with both the oldest data (from Fabricius 1596 to Hevelius 1660) and the most current data (VSX 2004–2023), so that we see no evidence for secular period or phase shifts. (We also present Fabricius' observations of P Cygni in 1602.)

We report the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ 287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ± 0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ 287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ 287 as well as the dense monitoring sample of Krakow.

RW Aurigae is a young stellar system containing a classical T Tauri star as the primary component. It shows deep, irregular dimmings, first detected in 2010. At the University Observatory Jena, we carried out optical follow‐up observations. We performed multiband (BVRI) photometry of the system with the Cassegrain‐Teleskop‐Kamera II and the Schmidt‐Teleskop‐Kamera between September 2016 and April 2019, as well as spectroscopy, using the Fibre Linked ÉCHelle Astronomical Spectrograph between September 2016 and April 2018. We present the apparent photometry of RW Aur, which is consistent with and complementary to photometric data from the American Association of Variable Star Observers. The V‐band magnitude of RW Aur changed by up to three magnitudes during the timespan of our monitoring campaign. For the observing epochs 2016/2017 and 2017/2018 we report a decreasing brightness, while in the epoch 2018/2019 the system remained in a relatively constant bright state. In the color‐magnitude diagram, we see that RW Aur lies close to a track for grey extinction. The spectra show a decreasing equivalent width (EW) of the emission line for decreasing brightness, whereas the EW of the line increases, indicating an increased outflow activity during the obscuration. Both give further evidence for the favored theory that the obscurations are caused by a hot dusty wind emerging from the inner disk.