We perform a search for faint, common proper motion companions of Hipparcos stars using the recently published Lepine-Shara Proper Motion-North catalog of stars with proper motion μ > 0.15'' yr-1. Our survey uncovers a total of 521 systems with angular separations 3'' 15.0. Our census is statistically complete for secondaries with angular separations 20'' 1000 AU. We observe that the distribution in orbital separations is consistent with Opik's law, f(s) ds ~ s-1 ds, only up to a separation s ≈ 4000 AU, beyond which it follows a more steeply decreasing power law f(s) ds ~ s-l ds with l = 1.6 ± 0.1. We also find that the luminosity function of the secondaries is significantly different from that of the single stars' field population, showing a relative deficiency in low-luminosity (8 < MV < 14) objects. The observed trends suggest either a formation mechanism biased against low-mass companions, or a disruption over time of systems with low gravitational binding energy.

New Distant Companions to Known Nearby Stars. II. Faint Companions of Hipparcos Stars and the Frequency of Wide Binary Systems

We analyze the K band luminosities of a sample of galactic long-period variables using parallaxes measured by the Hipparcos mission. The parallaxes are in most cases re-computed from the Hipparcos Intermediate Astrometric Data using improved astrometric fits and chromaticity corrections. The K band magnitudes are taken from the literature and from measurements by COBE, and are corrected for interstellar and circumstellar extinction. The sample contains stars of several spectral types: M, S and C, and of several variability classes: Mira, semiregular SRa, and SRb. We find that the distribution of stars in the period-luminosity plane is independent of circumstellar chemistry, but that the different variability types have different P-L distributions. Both the Mira variables and the SRb variables have reasonably well-defined period-luminosity relationships, but with very different slopes. The SRa variables are distributed between the two classes, suggesting that they are a mixture of Miras and SRb, rather than a separate class of stars. New period-luminosity relationships are derived based on our revised Hipparcos parallaxes. The Miras show a similar period-luminosity relationship to that found for Large Magellanic Cloud Miras by Feast et al. (1989). The maximum absolute K magnitude of the sample is about -8.2 for both Miras and semi-regular stars, only a little fainter than the expected AGB limit. We show that the stars with the longest periods (P>400d) have high mass loss rates and are almost all Mira variables.

/pdf/reprocessing-the-hipparcos-data-for-evolved-stars-iii-162p992cq7.pdf

Reprocessing the Hipparcos data for evolved stars III Revised Hipparcos period-luminosity relationship for galactic long-period variable stars

We perform a search for faint, common proper motion companions of Hipparcos stars using the recently published LSPM-north catalog of stars with proper motion mu>0.15 arcsec/yr. Our survey uncovers a total of 521 systems with angular separations 3 arcsec 15.0. Our census is statistically complete for secondaries with angular separations 20 arcsec 1,000 AU. We observe that the distribution in orbital separations is consistent with Opik's law f(s) ds ~ s^{-1} ds only up to separation s \approx 3,000 AU, beyond which it follows a more steeply decreasing power law f(s) ds ~ s^{-l} ds with l=1.6+/-0.1. We also find that the luminosity function of the secondaries is significantly different from that of the single stars field population, showing a relative deficiency in low-luminosity (8<M_V<14) objects. The observed trends suggest either a formation mechanism biased against low-mass companions, or a disruption over time of systems with low gravitational binding energy.

New Distant Companions to Known Nearby Stars. II. Faint companions of Hipparcos stars and the frequency of wide binary systems

We report our measurement of the rate of change of period with time () for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have finally obtained a 4 σ measurement observed = (4.27 ± 0.80) × 10-15 s s-1. Taking into account the proper-motion effect of proper = (7.0 ± 2.0) × 10-16 s s-1, we obtain a rate of change of period with time of = (3.57 ± 0.82) × 10-15 s s-1. This value is consistent with the cooling rate in our white dwarf models only for cores of C or C/O. With the refinement of the models, the observed rate of period change can be used to accurately measure the ratio of C/O in the core of the white dwarf.

/pdf/measuring-the-evolution-of-the-most-stable-optical-clock-g-541aiq9dbp.pdf

Measuring the Evolution of the Most Stable Optical Clock G 117-B15A

Context: Observations at the radio continuum band below the gigahertz band are key when the nature and properties of nonthermal sources are investigated because their radio radiation is strongest at these frequencies. The low radio frequency range is therefore the best to spot possible counterparts to very high-energy (VHE) sources: relativistic particles of the same population are likely to be involved in radio and high-energy radiation processes. Some of these counterparts to VHE sources can be stellar sources. Aims: The Cygnus region in the northern sky is one of the richest in this type of sources that are potential counterparts to VHE sources. We surveyed the central ~15sq deg of the Cygnus constellation at the 325 and 610~MHz bands with angular resolutions and sensitivities of 10" and 6", and 0.5 and 0.2 mJy/beam, respectively. Methods: The data were collected during 172 hours in 2013 - 2017, using the Giant Metrewave Radio Telescope (GMRT) with 32MHz bandwidth, and were calibrated using the SPAM routines. The source extraction was carried out with the PyBDSF tool, followed by verification through visual inspection of every putative catalog candidate source in order to determine its reliability. Results: In this first paper we present the catalog of sources, consisting of 1048 sources at 325 MHz and 2796 sources at 610MHz. By cross-matching the sources from both frequencies with the objects of the SIMBAD database, we found possible counterparts for 143 of them. Most of the sources from the 325-MHz catalog (993) were detected at the 610MHz band, and their spectral index alpha was computed adopting S(nu) ~ nu^alpha. The maximum of the spectral index distribution is at alpha=-1, which is characteristic of nonthermal emitters and might indicate an extragalactic population.

/pdf/cygnus-survey-with-the-giant-metrewave-radio-telescope-at-37f8j4d297.pdf

Cygnus survey with the Giant Metrewave Radio Telescope at 325 and 610 MHz: the catalog

We describe the derivation of periodicities from visual data for long-period variables, and give expected errors for the derived amplitude, phase and frequency. We extend this analysis by using a moving window to deduce variation in phase and amplitude over time. The method is demonstrated on the Mira-type variable T Cas, and shows evidence that the phase of the first harmonic (period 222.4 d) varies relative to the fundamental (period 444.8 d) with a period of approximately 3000 d. Our analysis parallels, but is completely independent of, the work of Szatmary, Gal & Kiss and Bedding et al., who both use an approach based on wavelet analysis.

Amplitude and phase changes in the light curves of long-period variables

We report on the discovery of a new variable star, MisV1147, by the MISAO Project and its unusual photometric variations. The light curve of the object is characterized by two distinct states, that is, a relatively calm, bright state and an active state during which repetitive fadings with large amplitudes of ∼2mag were observed. The fading events were associated with optical reddening. The object is identified with a catalogued Hα emission star, which has been confirmed by our spectroscopic observations. The Hα emission line is narrow and symmetric both in the bright and faint phases. The object has infrared colors analogous to T Tau stars or Herbig Ae/Be stars. In conjunction with the detection of a NaD absorption line and its position close to Cep OB1, we conclude that MisV1147 is a Herbig Be star with its spectral type of B2. Its optical-infrared spectral energy distribution is typical for Herbig Ae/Be stars, which supports this classification. The overall properties of the light curve are reminiscent of a UX Ori sub-group, showing Algol-type minima. The most noteworthy feature of MisV1147 is that it has a spectral type B2, whereas known UX Ori stars have spectral types later than B8. The object, furthermore, has one of the largest amplitudes of variations among known Herbig Ae/Be stars. Hence the object breaks the very strong correlation between the variation amplitude and the spectral type. This implies that dust clumps in circumstellar matter can significantly obscure a central object even in the early-type system.

/pdf/deep-fading-of-the-new-herbig-be-star-misv1147-476q2qcjia.pdf

Deep Fading of the New Herbig Be Star MisV1147

A list of 705 new Northern celestial hemisphere common proper-motion pairs as derived from the Second US Naval Observatory CCD Astrograph Catalog is presented, along with details of their separation, motion, brightness and colour. Objects of particular interest are noted, and the use of the catalogue for such work gauged.

New Northern hemisphere common proper-motion pairs

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Amplitude and phase changes in the light curves of long-period variables

Deep Fading of the New Herbig Be Star MisV1147

New Northern hemisphere common proper-motion pairs