Publications of the Astronomical Society of the Pacific

Smith, Myron A.

doi: 10.1088/1538-3873/aaf70bpmid: N/A

The recorded activity of γ Cas (B0.5 IVe) in the ultraviolet is important to an understanding of the mechanism behind this prototypical Be star’s high-energy activity, especially its hard X-ray emissions. The analysis here focuses first on the phasing of ultraviolet and optical light curves from different epochs. The rotational interpretation of the 1.22 d optical signal is justified in part on this phasing. Next, observations of “migrating subfeatures” are detailed, which traverse blue to red across line profiles in high-quality spectra. These are likely to be proxies for surface magnetic fields, which have not been detected yet by spectropolarimetric means in rapidly rotating Be stars like γ Cas. Also, the important responses of the semi-forbidden resonance S IV line at λ1404.8 to simultaneous X-ray variations are analyzed. These results offer indirect support for the existence of small-scale magnetic fields on this Be star.

Coughlin, Michael W.; Ahumada, Tomás; Cenko, S. Bradley; Cunningham, Virginia; Ghosh, Shaon; Singer, Leo P.; Bellm, Eric C.; Burns, Eric; De, Kishalay; Goldstein, Adam; Golkhou, V. Zach; Kaplan, David L.; Kasliwal, Mansi M.; Perley, Daniel A.; Sollerman, Jesper;

Otarola, A.; De Breuck, C.; Travouillon, T.; Matsushita, S.; Nyman, L.-Å.; Wootten, A.; Radford, S. J. E.; Sarazin, M.; Kerber, F.; Pérez-Beaupuits, J. P.

doi: 10.1088/1538-3873/aafb78pmid:

Gao, Xin-hua

doi: 10.1088/1538-3873/ab010epmid: N/A

This paper presents an investigation on fundamental astrophysical properties of the Pleiades cluster (M 45) using high-precision astrometric and photometric data from the Gaia Data Release 2 (Gaia-DR2). To obtain reliable cluster members, a machine-learning (ML) method is used to compute membership probabilities for 31462 sample stars within a radius of 6.5° from the cluster center, both the astrometric and photometric data are taken into account. We obtain a total number of 1454 likely cluster members with membership probabilities larger than 0.6, including a well-known white dwarf (LB 1497) with a high membership probability of ∼0.96. We find a well-defined relationship between the parallaxes and proper motions of the cluster members, the most likely explanation for the relationship is that the depth effect of the cluster along the line of sight must be taken into consideration. Using Monte Carlo simulations, the most likely distance, proper motion, and radial velocity of the cluster are determined to be D = 136.0 ± 0.1 pc, () = (+20.141 ± 0.093, −45.536 ± 0.081) mas yr−1, and , respectively. It is found that the likely cluster members extend outward to a limiting radius of Rlim = 310′ ± 12′ (12.3 ± 0.5 pc) from the cluster center, and the total mass of the cluster within this radius is Mtot = 721 ± 93 M⊙. We find clear evidence for the presence of spatial mass segregation in this young cluster by analyzing the photometry and spatial positions of the likely cluster members. Interestingly, we also find that four high-mass cluster members with high membership probabilities (>0.99) are being ejected from the inner region of the cluster, they may have formed via close encounters between single and binary stars.

Loper, Robert D.

doi: 10.1088/1538-3873/ab028epmid: N/A

The Drake equation is a calculation providing an upper bound on the likely number of intelligent species in our galaxy. In order to reconcile a potentially high occurrence of intelligent extraterrestrial species with the current non-observation of them, we frequently resort to some Great Filter which represents some inevitable, cataclysmic fate (such as nuclear war, pandemic, or asteroid impact) that tends to await enough worlds to negate the expectation that the galaxy ought to be teeming with intelligent life. This paper is intended to examine one potential Great Filter for electronic-based civilizations, the impact of a Carrington-class coronal mass ejection (CME) from the Sun. Carrington-class CMEs are classified as “once in a century” events caused by our Sun; this appears to place a time limit, following the development of a civilization dependent on electronic devices, either for hardening electronics against the geomagnetically induced currents that result from CMEs or for beginning interplanetary colonization.

Marco, F. J.; Martínez, M. J.; López, J. A.

doi: 10.1088/1538-3873/aaed5dpmid: N/A

The Gaia mission will provide a six-parameter solution for millions of stars, including a tridimensional map of our Galaxy. The estimation of distances has been made for the Tycho-Gaia Astrometric Solution (TGAS), while to contrast the proper motions it is interesting to consider positions from the different Gaia Data Release with older ones given in ground-based massive catalogs. This process has been followed to build, for example, the PMA catalog using the 2MASS. Our aim is to improve the positions of this catalog (although the process is applicable to any other). The first stage, presented here, consists of carrying out a three-dimensional study using vector spherical harmonics (VSH) development of the systematisms in position for the stars common with Hipparcos-2; we take into account the distances, magnitudes, and spectral types. To this aim, we use linear polynomial regression of first order that fits vector fields and the derivatives of their components. We verify that the coefficients of the developments of first order have different behavior according to the characteristics of stars and distances. To deepen the study, we focus on the conservative component of the field, applying the Helmholtz theorem. Each potential function is obtained solving a Poisson equation on the sphere, after finding the divergence of the corresponding vector field. Both vector and potential fields present patterns, at certain points, that depend on the three considered parameters (distance, magnitude, and spectral type); their sources and shrinks correspond to maxima and minima. In this sense, we observe that these critical points are also critical points of the surface that represents the VT magnitude of Tycho-2, which makes sense because this catalog was used in the reduction of 2MASS positions. Finally, we selected some stars near the critical points of the vector fields and apply the adjustments obtained in the previous sections. The difference with the positions in DR1 allows us to compare the proper motions: those from the PMA and those induced after our corrections.

Bosco, F.; Pott, J.-U.; Schödel, R.

doi: 10.1088/1538-3873/ab019fpmid: N/A

Adaptive optics (AO) systems and image reconstruction algorithms are indispensable tools when it comes to high-precision astrometry. In this paper, we analyze the potential of combining both techniques, i.e., by applying image reconstruction on partially AO-corrected short exposures. Therefore we simulate speckle clouds with and without AO corrections and create synthetic observations. We apply holographic image reconstruction to the obtained observations and find that (i) the residual wavefronts decorrelate slowlier and to a lower limit when AO systems are used, (ii) the same reference stars yield a better reconstruction, and (iii) using fainter reference stars we achieve a similar image quality. These results suggest that holographic imaging of speckle observations is feasible with ∼2–3× longer integration times and ∼3 mag fainter reference stars, to obtain diffraction-limited imaging from low-order AO systems that are less restricted in sky coverage than typical high-order AO systems.

Lozi, Julien; Jovanovic, Nemanja; Guyon, Olivier; Chun, Mark; Jacobson, Shane; Goebel, Sean; Martinache, Frantz

doi: 10.1088/1538-3873/ab046apmid: N/A

Wavefront sensing and control are important for enabling one of the key advantages of using large apertures, namely higher angular resolution. Pyramid wavefront sensors are becoming commonplace in new instrument designs owing to their superior sensitivity. However, one remaining roadblock to their widespread use is the fabrication of the pyramidal optic. This complex optic is challenging to fabricate due to the pyramid tip, where four planes need to intersect at a single point. Thus far, only a handful of these have been produced due to the low yields and long lead times. To address this, we present an alternative implementation of the pyramid wavefront sensor which relies instead on two roof prisms. Such prisms are easy and inexpensive to source. We demonstrate the successful operation of the roof prism pyramid wavefront sensor on an 8 m class telescope, at visible and near-infrared wavelengths, for the first time using a SAPHIRA HgCdTe detector without modulation for a laboratory demonstration, and elucidate how this sensor can be used more widely on wavefront control test benches and instruments.

Hua, Zhang; Rong, Jiao; Luping, Xu; chengyang, Xu; peng, Mi

doi: 10.1088/1538-3873/aafc73pmid: N/A

The ephemeris of a pulsar is stable for a long time, which allows navigation based on pulsar orientation to be vector feasible. The formation of a satellite navigation model using the orientation vector of an X-ray pulsar signal is presented in this paper. To obtain the time difference of arrival (TDOA), a new estimation method is constructed, which can measure the photon sequence of an X-ray pulsar signal and is based on the fast Fourier transform (FFT). Next, three new observation variables are constructed. The variables are satellite phase incrementation; the angle between the satellite baseline and the pulsar direction vector; and the angle between the plane spanned by three satellite baselines and the pulsar direction vector. All three variables, along with the TDOA of the X-ray pulsar signal, are utilized to determine the orbit. The position and velocity of the satellite formations are estimated by using the adaptive divided difference filter (ADDF) to eliminate nonlinearity. Several simulation cases are designed to verify the proposed method.

Andersen, M. Fredslund; Handberg, R.; Weiss, E.; Frandsen, S.; Simón-Díaz, S.; Grundahl, F.; Pallé, P.

doi: 10.1088/1538-3873/aaff7cpmid: N/A

We present a description of “the Conductor,” an automated software package that handles all observations at the first Stellar Observations Network Group (SONG) node telescope at the Teide Observatory on the island of Tenerife. The idea was to provide a complete description on the automated procedures for target selection and execution of observations and to demonstrate how the SONG robotic telescope is being operated. The Conductor is a software package developed in Python and running on a server in Aarhus that makes use of a large set of database tables through which it communicates with the SONG nodes. Based on a number of selection criteria the Conductor is able to identify the optimum target to be observed at any given moment, taking into account local weather conditions and technical constraints. The Conductor has made it possible for the Hertzsprung SONG telescope to become a highly sophisticated and efficient robotic telescopic facility without human interaction. It can handle everything from principal investigators submitting their proposed targets with specific settings, to the data being available for download after the observations has been carried out. At present, and thanks to the availability of the Conductor, the first node of the SONG project can be considered a world leading robotic telescope with respect to needed human interactions, efficiency, and flexibility in observing strategy.