Direction Of Proper Motion Research Articles

Collision of protostellar jets in the star-forming region IC 1396N

Context. The bright-rimmed cloud IC 1396N is believed to host one of the few known cases where two bipolar CO outflows driven by young stellar objects collide. The CO outflows are traced by chains of knots of H2 emission, with enhanced emission at the position of the possible collision. Aims. The aim of this work is to use the proper motions of the H2 knots to confirm the collision scenario. Methods. A second-epoch H2 image was obtained, and the proper motions of the knots were determined with a time baseline of ~11 yr. We also performed differential photometry on the images to check the flux variability of the knots. Results. For each outflow (N and S), we classified the knots as pre-collision or post-collision. The axes of the pre-collision knots, the position of the possible collision point, and the axes of the post-collision knots were estimated. The difference between the proper motion direction of the post-collision knots and the position angle from the collision point was also calculated. For some of the knots, we obtained the 3D velocity using the radial velocity derived from H2 spectra. Conclusions. The velocity pattern of the H2 knots in the area of interaction (post-collision knots) shows a deviation from that of the pre-collision knots, consistent with being a consequence of the interaction between the two outflows. This favours the interpretation of the IC 1396N outflows as a true collision between two protostellar jets instead of a projection effect.

Revisiting MOA 2013-BLG-220L: A Solar-type Star with a Cold Super-Jupiter Companion

Abstract We present the analysis of high-resolution images of MOA-2013-BLG-220, taken with the Keck adaptive optics system six years after the initial observation, identifying the lens as a solar-type star hosting a super-Jupiter-mass planet. The masses of planets and host stars discovered by microlensing are often not determined from light-curve data, while the star–planet mass ratio and projected separation in units of Einstein ring radius are well measured. High-resolution follow-up observations after the lensing event is complete can resolve the source and lens. This allows direct measurements of flux, and the amplitude and direction of proper motion, giving strong constraints on the system parameters. Due to the high relative proper motion, mas yr−1, the source and lens were resolved in 2019, with a separation of 77.1 ± 0.5 mas. Thus, we constrain the lens flux to . By combining constraints from the model and Keck flux, we find the lens mass to be at . With a mass ratio of the planet’s mass is determined to be at a separation of . The lens mass is much higher than the prediction made by Bayesian analysis that assumes all stars have an equal probability to host a planet of the measured mass ratio, and suggests that planets with mass ratios of a few times 10−3 are more common orbiting massive stars. This demonstrates the importance of high-resolution follow-up observations for testing theories like these.

Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event

Abstract We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555 (Kojima-1). We measure the microlens parallax vector using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this determination with the angular Einstein radius measured by VLTI-GRAVITY observations, we find that the lens is a star with mass at a distance D L = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is , so with currently available adaptive-optics instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite-parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.

A deep X-ray spectral imaging of the bow-shock pulsar wind nebula associated with PSR B1929+10

In this work, we study the X-ray bow-shock nebula powered by the mature pulsar PSR B1929+10 using data from XMM-Newton, with an effective exposure of ∼300 ks, offering the deepest investigation of this system thus far. We found the X-ray axial outflow extends as long as ∼8 arc minute behind the proper motion direction, which is a factor of two longer than the result reported in the previous study. Furthermore, we found evidence of two faint lateral outflows extending laterally with respect to the proper motion. We also found indications of spectral hardening along the axial outflow, suggesting that certain acceleration processes might occur along this feature.

Chandra measurements of the proper motion of the γ-ray pulsar J0633+0632

We measured the proper motion of a γ-ray radio-quiet pulsar J0633+0632 using Chandra observations performed in 2009 and 2017. The measured proper motion is 53 ± 15 mas yr−1. We found that the proper motion direction does not follow the extension of the J0633+0632 pulsar wind nebula. The J0633+0632 pulsar wind nebula therefore can be a jet-like feature or a misaligned outflow. We also discuss a possible birth cite of the pulsar.

The two tails of PSR J2055+2539 as seen by Chandra: Analysis of the nebular morphology and pulsar proper motion

We analyzed two Chandra observations of PSR J2055+2539 for a total integration time of ∼130 ks to measure the proper motion and study the two elongated nebular features of this source. We did not detect the proper motion, setting an upper limit of 240 mas yr−1 (3σ level), which translates into an upper limit on the transverse velocity of ∼700 km s−1, for an assumed distance of 600 pc. A deep Hα observation did not reveal the bow shock associated with a classical pulsar wind nebula, thus precluding an indirect measurement of the proper motion direction. We determined the main axes of the two nebulae, which are separated by an angle of 160.°8 ± 0.°7, using a new approach based on the rolling Hough transformation (RHT). We analyzed the shape of the first 8′ (out of the 12′ seen by XMM-Newton) of the brighter, extremely collimated nebula. Based on a combination of our results from a standard analysis and a nebular modeling obtained from the RHT, we find that the brightest nebula is curved on an arcmin scale and has a thickness ranging from ∼9″ to ∼31″ and a possible (single or multiple) helicoidal pattern. We could not constrain the shape of the fainter nebula. We discuss our results in the context of other known similar features and place particular emphasis on the Lighthouse nebula associated with PSR J1101−6101. We speculate that a peculiar geometry of the powering pulsar may play an important role in the formation of such features.

First experimental results on the feasibility of noise radar systems on fast moving platforms

Forward-looking radars are essential sensors for many fast moving platforms such as fighter aircraft and missiles. Despite its multiple benefits, noise radar has not yet been used for this task because of the low Doppler tolerance of its waveform and the associated need for computational intense Doppler compensation. This Letter presents the very first experimental results of a continuous-emission noise radar whose antennas are oriented along the direction of proper motion of a car operating as a radar platform at a significant speed. To the best of the authors' knowledge, no experiments of this kind have been published to date. Very likely, the results presented here are the first ones showing moving target detection by a noise radar on a fast moving platform.

Discovery of an X-ray nebula in the field of millisecond pulsar PSR J1911–1114

We have discovered an extended X-ray feature, apparently associated with millisecond pulsar (MSP) PSR J1911–1114. The feature, which extends for ∼1′, was discovered from an XMM-Newton observation; the radio timing position of PSR J1911–1114 is in the midpoint of the feature. The orientation of the feature is similar to the proper motion direction of PSR J1911–1114. Its X-ray spectrum can be well-modeled by an absorbed power law with a photon index of Γ = 1.8−+0.30.2. If this feature is confirmed to be a pulsar wind nebula (PWN), this will be the third case where an X-ray PWN has been found to be powered by a MSP.

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

ABSTRACT We have analysed the differences in positions of 9081 matched sources between the Gaia Data Release 2 (DR2) and very long baseline interferometry (VLBI) catalogues. The median position uncertainty of matched sources in the VLBI catalogue is a factor of two larger than the median position uncertainty in Gaia DR2. There are 9 per cent matched sources with statistically significant offsets between both catalogues. We found that the reported positional errors should be rescaled by a factor of 1.3 for VLBI and 1.06 for Gaia and, in addition, the Gaia errors should be multiplied by the square root of chi squared per degree of freedom in order to best fit the normalized position differences to the Rayleigh distribution. We have established that the major contributor to statistically significant position offsets is the presence of optical jets. Among the sources for which the jet direction was determined, the position offsets are parallel to the jet directions for 62 per cent of the outliers. Among the matched sources with significant proper motion, the fraction of objects with proper motion directions parallel to jets is a factor of three greater than on average. Such sources have systematically higher chi squared per degree of freedom. We explain these proper motions as a manifestation of the source position jitter caused by flares, which we predicted earlier. Therefore, the assumption that quasars are fixed points, and thus that differential proper motions determined with respect to quasar photocentres can be regarded as absolute proper motions, should be treated with great caution.

Planetary nebulae with UVIT: Far ultra-violet halo around the Bow Tie nebula (NGC 40)

Context. NGC 40 is a planetary nebula with diffuse X-ray emission, suggesting an interaction of the high-speed wind from WC8 central star (CS) with the nebula. It shows strong C IV 1550 Å emission that cannot be explained by thermal processes alone. We present here the first map of this nebula in C IV emission using broad band filters on the Ultra-Violet Imaging Telescope (UVIT). Aim. We aim to map the hot C IV-emitting gas and its correspondence with soft X-ray (0.3–8 keV) emitting regions in order to study the shock interaction between the nebula and the ISM. We also aim to illustrate the potential of UVIT for nebular studies. Methods. We carry out a morphological study of images of the nebula obtained at an angular resolution of about 1.3″ in four UVIT filter bands that include C IV 1550 Å and [C II] 2326 Å lines as well as UV continuum. We also make comparisons with X-ray, optical, and IR images from the literature. Results. The [C II] 2326 Å images show the core of the nebula with two lobes on either side of CS similar to [N II]. The C IV emission in the core shows similar morphology and extent to that of diffuse X-ray emission concentrated in nebular condensations. A surprising UVIT discovery is the presence of a large faint far UV (FUV) halo in an FUV filter with λeff of 1608 Å. The UV halo is not present in any other UV filter. The FUV halo is most likely due to UV fluorescence emission from the Lyman bands of H2 molecules. Unlike the optical and IR halo, the FUV halo trails predominantly towards the south-east side of the nebular core, opposite to the CS’s proper motion direction. Conclusions. Morphological similarity of C IV 1550 Å and X-ray emission in the core suggests that it results mostly from the interaction of strong CS wind with the nebula. The FUV halo in NGC 40 highlights the extensive existence of H2 molecules in the regions even beyond the optical and IR halos. Thus UV studies are important to estimate the amount of H2, which is probably the most dominant molecule and significant for mass-loss studies.

Absolute polarization determinations of 33 pulsars using the Green Bank Telescope

Absolute polarimetry observations of 33 pulsars were carried out with the Green Bank Telescope in the 1100-1900-MHz band using the Green Bank Ultimate Pulsar Processing Instrument. This group was selected to help complete a larger sample for which accurate proper-motion measurements were available. A combination of profile analysis using the core/double cone model and polarizationangle fitting methods were applied to estimate the “fiducial” longitude of the magnetic axis for each star and refer the linear polarization angle at that point to infinite frequency. As had been found previously, a number of the pulsars are found to have fiducial polarization directions that fall either along or at right angles to their proper-motion directions, whereas upwards of a third of the stars studied show alignments that are neither parallel nor orthogonal.

On the PSR B1133+16 optical counterpart★

The aim of this work is confirming the optical identification of PSR B1133+16, whose candidate optical counterpart was detected in Very Large Telescope (VLT) images obtained back in 2003. We used new deep optical images of the PSR B1133+16 field obtained with both the 10.4 m Gran Telescopio Canarias (GTC) and the VLT in the g' and B bands, respectively, to confirm the detection of its candidate optical counterpart and its coincidence with the most recent pulsar's radio coordinates. We did not detect any object at the position of the pulsar candidate counterpart (B~28), measured in our 2003 VLT images. However, we tentatively detected an object of comparable brightness in both the 2012 GTC and VLT images, whose position is offset by ~3.03" from that of the pulsar's candidate counterpart in the 2003 VLT images and lies along the pulsar's proper motion direction. Accounting for the time span of ~9 years between the 2012 quasi-contemporary GTC and VLT images and the 2003 VLT one, this offset is consistent with the yearly displacement of the pulsar due to its proper motion. Therefore, both the flux of the object detected in the 2012 GTC and VLT images and its position, consistent with the proper motion-corrected pulsar radio coordinates, suggest that we have detected the candidate pulsar counterpart that has moved away from its 2003 discovery position.

Pulsar spin-velocity alignment: further results and discussion

The reported alignment between the projected spin-axes and proper motion directions of pulsars is revisited in the light of new data from Jodrell Bank and Effelsberg. The present investigation uses 54 pulsars, the largest to date sample of pulsars with proper motion and absolute polarization, to study this effect. Our study has found strong evidence for pulsar spin–velocity alignment, excluding that those two vectors are completely uncorrelated, with >99 per cent confidence. Although we cannot exclude the possibility of orthogonal spin–velocity configurations, comparison of the data with simulations shows that the scenario of aligned vectors is more likely than that of the orthogonal case. Moreover, we have determined the spread of velocities that a spin-aligned and spin-orthogonal distribution of kicks must have to produce the observed distribution of spin–velocity angle offsets. If the observed distribution of spin–velocity offset angles is the result of spin-aligned kicks, then we find that the distribution of kick-velocity directions must be broad with ; if the orthogonal-kick scenario is assumed, then the velocity distribution is much narrower with . Finally, in contrast to previous studies, we have performed robustness tests on our data, in order to determine whether our conclusions are the result of a statistical and/or systematic bias. The conclusion of a correlation between the spin and velocity vectors is independent of a bias introduced by subsets in the total sample. Moreover, we estimate that the observed alignment is robust to within 10 per cent systematic uncertainties on the determination of the spin-axis direction from polarization data.

XMM-NEWTONOBSERVATION OF PSR B2224+65 AND ITS JET

We have investigated the pulsar PSR B2224+65 and its X-ray jet with XMM-Newton. Apart from the long X-ray jet which is almost perpendicular to the direction of proper motion, a putative extended feature at the pulsar position, which oriented in the opposite direction of the proper motion, is also suggested by this deep X-ray imaging. Non-detection of any coherent X-ray pulsation disfavors the magnetospheric origin of the X-rays observed from the position of PSR B2224+65 and hence suggest that the interpretation of pulsar wind nebula is more viable. We have also probed the origin of PSR B2224+65 and identified a runaway star, which possibly originated from the Cygnus OB9 association, as a candidate for the former binary companion of the neutron star's progenitor.

ON THE CONNECTION OF THE APPARENT PROPER MOTION AND THE VLBI STRUCTURE OF COMPACT RADIO SOURCES

Many of the compact extragalactic radio sources that are used as fiducial points to define the celestial reference frame are known to have proper motions detectable with long-term geodetic/astrometric Very Long Baseline Interferometry (VLBI) measurements. These changes can be as high as several hundred micro-arcseconds per year for certain objects. When imaged with VLBI at milli-arcsecond (mas) angular resolution, these sources (radio-loud active galactic nuclei) typically show structures dominated by a compact, often unresolved "core" and a one-sided "jet". The positional instability of compact radio sources is believed to be connected with changes in their brightness distribution structure. For the first time, we test this assumption in a statistical sense on a large sample, not only for individual objects. We investigate a sample of 62 radio sources for which reliable long-term time series of astrometric positions as well as detailed 8-GHz VLBI brightness distribution models are available. We compare the characteristic direction of their extended jet structure and the direction of their apparent proper motion. We present our data and analysis method, and conclude that there is indeed a correlation between the two characteristic directions. However, there are cases where the ~1-10-mas scale VLBI jet directions are significantly misaligned with respect to the apparent proper motion direction.

The pulsar B2224+65 and its jets: a two epoch X-ray analysis

We present an X-ray morphological and spectroscopic study of the pulsar B2224+65 and its apparent jet-like X-ray features based on two epoch Chandra observations. The main X-ray feature, which shows a large directional offset from the ram-pressure confined pulsar wind nebula (Guitar Nebula), is broader in apparent width and shows evidence for spectral hardening (at 95 percent confidence) in the second epoch compared to the first. Furthermore, the sharp leading edge of the feature is found to have a proper motion consistent with that of the pulsar (~180 mas yr-1). The combined data set also provides evidence for the presence of a counter feature, albeit substantially fainter and shorter than the main one. Additional spectral trends along the major and minor axes of the feature are only marginally detected in the two epoch data, including softening counter to the direction of proper motion. Possible explanations for the X-ray features include diffuse energetic particles being confined by an organized ambient magnetic field as well as a simple ballistic jet interpretation; however, the former may have difficulty in explaining observed spectral trends between epochs and along the feature's major axis whereas the latter may struggle to elucidate its linearity. Given the low counting statistics available in the two epoch observations, it remains difficult to determine a physical production scenario for these enigmatic X-ray emitting features with any certainty.

HST/WFPC2 observations of the LMC pulsar PSR B0540–69

The study of the younger, and brighter, pulsars is important to understand the optical emission properties of isolated neutron stars. PSRB0540-69, the second brightest (V~22) optical pulsar, is obviously a very interesting target for these investigations. The aim of this work is threefold: constraining the pulsar proper motion and its velocity on the plane of the sky through optical astrometry, obtaining a more precise characterisation of the pulsar optical spectral energy distribution (SED) through a consistent set of multi-band, high-resolution, imaging photometry observations, measuring the pulsar optical phase-averaged linear polarisation, for which only a preliminary and uncertain measurement was obtained so far from ground-based observations. We performed high-resolution observations of PSRB0540-69 with the WFPC2 aboard the HST, in both direct imaging and polarimetry modes. From multi-epoch astrometry we set a 3sigma upper limit of 1 mas/yr on the pulsar proper motion, implying a transverse velocity <250 km/s at the 50 kpc LMC distance. Moreover, we determined the pulsar absolute position with an unprecedented accuracy of 70 mas. From multi-band photometry we characterised the pulsar power-law spectrum and we derived the most accurate measurement of the spectral index (0.70+/-0.07) which indicates a spectral turnover between the optical and X-ray bands. Finally, from polarimetry we obtained a new measurement of the pulsar phase-averaged polarisation degree (16+/-4%),consistent with magnetosphere models depending on the actual intrinsic polarisation degree and depolarisation factor, and we found that the polarisation vector (22+/-12deg position angle) is possibly aligned with the semi-major axis of the pulsar-wind nebula and with the apparent proper motion direction of its bright emission knot.

Further Evidence for Alignment of the Rotation and Velocity Vectors in Pulsars

We re-examine the evidence for alignment of the proper motion and fiducial polarization-angle directions in radio pulsars given by Johnston et al., and we find that the case is probably stronger than this paper asserts. Other alignments are examined using the published literature and recent Arecibo polarimetry, providing an enlarged case that pulsar rotation axis and supernovae kick directions are aligned or at birth. Pulsars' orthogonal polarization modes complicate fixing the orientation of such kicks, but we note that determining the absolute geometry of the polarization modes is a key objective for understanding the physical origins of pulsar emission.

X-ray emission properties of the old pulsar PSR B2224+65

Using archival Chandra data we studied the X-ray emission properties of PSR B2224+65 and its environment. Albeit limited by photon statistics the spectral analysis suggests that the bulk of the emission from PSR B2224+65 is non-thermal. Fitting a power-law to the observed energy spectrum yields a photon index of $\Gamma=1.58^{+0.43}_{-0.33}$. The possible origin of the non-thermal pulsar emission is discussed in the context of the outer-gap model. We did not find any evidence for a compact nebula around PSR B2224+65 though the Chandra data reveal the existence of an extended feature which appears to be associated with PSR B2224+65. It extends from the pulsar position about 2 arcmin to the north-west. Its orientation deviates by $\sim118^{\circ}$ from the pulsar's proper motion direction. Investigating its energy spectrum shows that the emission of this extended feature is much harder than that of the pulsar itself and is non-thermal in nature.

Subaru optical observations of the two middle-aged pulsars PSR B0656+14 and Geminga

Aims.We carried out a deep subarcsecond BRI imaging of the two middle-aged pulsars to establish their properties in the optical range. Methods.Astrometry and photometry methods are applied to identify the pulsars and to measure their fluxes. We also reanalyze archival ESO/NTT and HST broadband data and find that some published fluxes for Geminga were estimated inaccurately. The resulting dereddened broadband spectra in the near-IR-UV range are analyzed and compared with available data from the radio through gamma-rays.Results.Both pulsars are detected at 10σ level. Geminga is for the first time reliably detected in the I band with a magnitude of 25. The dereddened spectra of both pulsars are remarkably similar to each other and show significant flux increases towards the far-UV and near-IR, and a wide flux excess in bands. This suggests a multicomponent structure of the optical emission. The nonthermal power law component of the pulsar magnetospheric origin dominates in the most part of the optical range. For PSR B0656+14 it is compatible with a low energy extension of the power law tail seen in hard X-rays. For Geminga the respective extension overshoots by a factor of 100 the nonthermal optical flux, which has a less steep spectral slope than in X-rays. This implies a spectral break at a photon energy ~1 keV. The flux increases towards the far-UV are compatible with contributions of the Rayleigh-Jeans parts of the blackbody components from whole surfaces of the neutron stars dominating in soft X-rays. The excess, which is most significant for PSR B0656+14, suggests a third spectral component of still unidentified origin. Faint, a few arcseconds in size nebulae extended perpendicular to the proper motion directions of the pulsars, are seen around both objects in our deepest I band images. They can be optical counterparts of the bow-shock head of Geminga and of the tentative pulsar wind nebula of PSR B0656+14 observed in X-rays.