Trigonometric Distances Research Articles

Perseus arm – a new perspective on star formation and spiral structure in our home galaxy

ABSTRACT Expansion of (sub)millimetre capabilities to high angular resolution offered with interferometers allows to resolve giant molecular clouds (GMCs) in nearby galaxies. This enables us to place the Milky Way in the context of other galaxies to advance our understanding of star formation in our own Galaxy. We, thus, remap 12CO (1–0) data along the Perseus spiral arm in the outer Milky Way to a fixed physical resolution and present the first spiral arm data cube at a common distance as it would be seen by an observer outside the Milky Way. To achieve this goal, we calibrated the longitude–velocity structure of 12CO gas of the outer Perseus arm based on trigonometric distances and maser velocities provided by the BeSSeL survey. The molecular gas data were convolved to the same spatial resolution along the whole spiral arm and regridded on to a linear scale map with the coordinate system transformed to the spiral arm reference frame. We determined the width of the Perseus spiral arm to be 7.8 ± 0.2 km s−1 around the kinematic arm centre. To study the large-scale structure, we derived the 12CO gas mass surface density distribution of velocities, shifted to the kinematic arm centre, and arm length. This yields a variation of the gas mass surface density along the arm length and a compression of molecular gas mass at linear scale. We determined a thickness of ∼63 pc on average for the Perseus spiral arm and a centroid of the molecular layer of 8.7 pc.

Two-component Magnetic Field along the Line of Sight to the Perseus Molecular Cloud: Contribution of the Foreground Taurus Molecular Cloud

Abstract Optical stellar polarimetry in the Perseus molecular cloud direction is known to show a fully mixed bimodal distribution of position angles across the cloud. We study the Gaia trigonometric distances to each of these stars and reveal that the two components in position angles trace two different dust clouds along the line of sight. One component, which shows a polarization angle of −37.°6 ± 35.°2 and a higher polarization fraction of 2.0 ± 1.7 %, primarily traces the Perseus molecular cloud at a distance of 300 pc. The other component, which shows a polarization angle of +66.°8 ± 19.°1 and a lower polarization fraction of 0.8 ± 0.6 %, traces a foreground cloud at a distance of 150 pc. The foreground cloud is faint, with a maximum visual extinction of ≤1 mag. We identify that foreground cloud as the outer edge of the Taurus molecular cloud. Between the Perseus and Taurus molecular clouds, we identify a lower-density ellipsoidal dust cavity with a size of 100–160 pc. This dust cavity is located at l = 170°, b = −20°, and d = 240 pc, which corresponds to an HI shell generally associated with the Per OB2 association. The two-component polarization signature observed toward the Perseus molecular cloud can therefore be explained by a combination of the plane-of-sky orientations of the magnetic field both at the front and at the back of this dust cavity.

The Volume-complete Sample of M Dwarfs with Masses 0.1 ≤ M/M⊙ ≤ 0.3 within 15 Parsecs

Abstract M dwarfs with masses 0.1 ≤ M/M ⊙ ≤ 0.3 are under increasing scrutiny because these fully convective stars pose interesting astrophysical questions regarding their magnetic activity and angular momentum history. They also afford the most accessible near future opportunity to study the atmospheres of terrestrial planets. Because they are intrinsically low in luminosity, the identification of the nearest examples of these M dwarfs is essential for progress. We present the volume-complete, all-sky list of 512 M dwarfs with masses 0.1 ≤ M/M ⊙ ≤ 0.3 and with trigonometric distances placing them within 15 pc (π trig ≥ 66.67 mas) from which we have created a sample of 413 M dwarfs for spectroscopic study. We present the mass function for these 512 M dwarfs, which increases with decreasing stellar mass in linear mass space, but is flat in logarithmic mass space. As part of this sample, we present new V J R KC I KC photometry for 17 targets, measured as a result of the RECONS group’s long-term work at the CTIO/SMARTS 0.9 m telescope. We also note the details of targets that are known to be members of multiple systems and find a preliminary multiplicity rate of 21% ± 2% for the primary M dwarfs in our sample when considering known stellar and brown dwarf companions at all separations from their primaries. We further find that 43 ± 2% of all M dwarfs with masses 0.1 ≤ M/M ⊙ ≤ 0.3 are found in multiple systems with primary stars of all masses within 15 pc.

Interarm islands in the Milky Way – the one near the Cygnus spiral arm

ABSTRACT This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the ‘Outer Norma’ arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literature – see column 8 in Table 1 here, having been obtained via the existing networks (US VLBA, the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm and those congregating within an ‘interarm island’ located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus, we delineate an interarm island (6 × 2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small ‘Local Orion arm’ (4 × 2 kpc) found earlier between the Perseus and Sagittarius arms and of the old ‘Loop’ (2 × 0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, H II regions, H I gas, young stars, CO 1–0 gas).

Measurement of the distance to the central stars of Nebulae by using Expansion methods with Alladin Sky Atlas

The usual methods of distance determination in Astronomy parallax and Spectroscopic with Expansion Methods are seldom applicable to Nebulae. In this work determination of the distances to individual Nebulae are calculated and discussed. The distances of Nebulae to the Earth are calculated. The accuracy of the distance is tested by using Aladin sky Atlas, and comparing Nebulae properties were derived from these distance made with statistical distance determination. The results showed that angular Expansions may occur in a part of the nebulae that is moving at a velocity different than the observed velocity. Also the results of the comparison of our spectroscopic distances with the trigonometric distances is that the spectroscopic distances are 55% larger. Since using trigonometric parallaxes with large relative measurement errors can introduce systematic errors, we carried out a Monte Carlo simulation of the biases introduced by selection effects and measurement errors. It turns out that a difference between both distance scales of the observed size is expected for the present day data if the underlying distance scales are identical.

Spatial and velocity offsets of Galactic masers from the centres of spiral arms

ABSTRACT Some theories about the spiral arms of galaxies predict an offset between different tracers of star formation. Our goal in this paper is to find such an offset between the observed locations of radio masers and the locations of the arms, using a recent four-arm model fitted to the CO 1–0 gas. Our method is to compare a recent global four-arm spiral model (as fitted to the arms’ tangents in the observed broad CO 1–0 gas) with the recent results for the trigonometric distances of radio masers, for the main arms (Cygnus–Norma, Perseus, Sagittarius–Carina, Scutum and Norma). Our results indicate that most radio masers are near the inner edge of each spiral arm (towards the Galactic Centre). These masers are offset from the model arm (where the broad CO 1–0 molecular region resides), by 0.34 ± 0.06 kpc inward. In radial velocity space, the median offset between masers and the CO-fitted model is around 10 ± 1 km s–1. Based on the fact that the masers are observed here to be radially inward of the broad CO gas in the Cygnus arm at 15 kpc along the Galactic meridian, the corotation radius of the Milky Way disc is >15 kpc distant from the Galactic Centre and the density wave’s angular pattern speed is <15 km s–1 kpc–1. The pitch angle of the arm should be measured using many arm tracers, and located on both sides of the Galactic meridian, to ensure better precision and to avoid a bias pertinent to a single tracer.

Radial Velocities, Space Motions, and Nearby Young Moving Group Memberships of Eleven Candidate Young Brown Dwarfs∗

Abstract We present new radial velocity (RV) measurements for 11 candidate young very-low-mass stars and brown dwarfs, with spectral types from M7 to L7. Candidate young objects were identified by features indicative of low surface gravity in their optical and/or near-infrared spectra. RV measurements are derived from high-resolution (R =λ/Δλ = 20,000) J-band spectra taken with NIRSPEC at the Keck Observatory. We combine RVs with proper motions and trigonometric distances to calculate three-dimensional space positions and motions and to evaluate membership probabilities for nearby young moving groups (NYMGs). We propose 2MASS J00452143+1634446 (L2β, J = 13.06) as an RV standard given the precision and stability of measurements from three different studies. We test the precision and accuracy of our RV measurements as a function of spectral type of the comparison object, finding that RV results are essentially indistinguishable even with differences of ±5 spectral subtypes. We also investigate the strengths of gravity-sensitive K i lines at 1.24–1.25 μm and evaluate their consistency with other age indicators. We confirm or reconfirm four brown dwarf members of NYMGs—2MASS J00452143+1634446, WISE J00470038+6803543, 2MASS J011747483403258, and 2MASS J193555952846343—and their previous age estimates. We identify one new brown dwarf member of the Carina-Near moving group, 2M2154−10. The remaining objects do not appear to be members of any known NYMGs, despite their spectral signatures of youth. These results add to the growing number of very-low-mass objects exhibiting signatures of youth that lack likely membership in a known NYMG, thereby compounding the mystery regarding local, low-density star formation.

Astronomical distance scales

Overview of the determination of astronomical distances from a metrological standpoint. Distances are considered from the Solar System (planetary distances) to extragalactic distances, with a special emphasis on the fundamental step of the trigonometric stellar distances and the giant leap recently experienced in this field thanks to the ESA space astrometry missions Hipparcos and Gaia.

BANYAN. XII. New Members of Nearby Young Associations from GAIA–Tycho Data

Abstract We present a search for stellar members of young associations within 150 pc of the Sun, based on TGAS and an updated version of the BANYAN Σ software to determine Bayesian membership probabilities that includes Gaia–2MASS color-magnitude diagrams. We identify 32 new F0–M3-type bona fide members of the 10–200 Myr old Sco-Cen, Carina, Tucana-Horologium, Columba, and Octans associations and the AB Doradus, β Pictoris, and Carina-Near moving groups. These new bona fide members have measurements of their full kinematics and literature data consistent with a young age. We also confirm the membership of 66 previously known candidate members using their Gaia–Tycho trigonometric distances or new literature radial velocities, and identify 219 additional new candidate members, most of which do not yet have a radial velocity measurement. This work is the first step toward a completeness-corrected survey of young association members based on Gaia DR2 in the near future.

A Pre-Gaia DR2 Survey for Nearby M Dwarfs in Young Associations

In this research note we identify 130 new M-type candidate members of young associations with the BANYAN $\Sigma$ tool and recently published trigonometric distances from RECONS and URAT-South. We identify a white dwarf candidate in the AB Doradus moving group, but determine that its cooling age is too large and reject it as a member. Three stars (G 13-39, LHS 2935 and G 152-1) now have complete kinematics and are strong candidate members in the AB Doradus and Carina-Near moving groups, but still lack a confirmation of their young age independent of their kinematics.

A preliminary comparison of photometric (MWSC) and trigonometric (TGAS) distances of open cluster stars

Abstract The goal of this researchwas to compare the open cluster photometric distance scale of the global survey of star clusters in the MilkyWay (MWSC) with the distances derived fromtrigonometric parallaxes fromthe Gaia DR1/TGAS catalogue and to investigate towhich degree and extent both scales agree.We compared the parallax-based and photometrybased distances of 5743 cluster stars selected as members of 1118 clusters based on their kinematic and photometric MWSC membership probabilities. We found good overall agreement between trigonometric and photometric distances of open cluster stars. The residuals between them were small and unbiased up to log(d, [pc]) ≈ 2.8. If we considered only the most populated clusters and used cluster distances obtained from the mean trigonometric parallax of their MWSC members, the good agreement of the distance scales continued up to log(d, [pc]) ≈ 3.3.

Metallicity distribution functions using Gaia-DR1 data

AbstractThe metallicity distribution function (MDF) of the stellar components of the Milky Way hold valuable information regarding the processes that have taken place in the evolution of our Galaxy. In this proceeding, we investigate updates concerning the MDF now that the Tycho-Gaia Astrometric Solution (TGAS) catalogue has been released and that trigonometric distances are available. In particular, vertical changes and skewness of the MDF are investigated, together with the properties of the metal-rich stars in the sample, at different positions in the Galaxy.

Astrometry of OH/IR Stars Using 1612 MHz Hydroxyl Masers. I. Annual Parallaxes of WX Psc and OH138.0+7.2

Abstract We report on the measurement of the trigonometric parallaxes of 1612 MHz hydroxyl masers around two asymptotic giant branch stars, WX Psc and OH 138.0+7.2, using the NRAO Very Long Baseline Array with in-beam phase referencing calibration. We obtain a 3σ upper limit of ≤5.3 mas on the parallax of WX Psc, corresponding to a lower limit distance estimate of ≳190 pc. The obtained parallax of OH 138.0+7.2 is 0.52 ± 0.09 mas (±18%), corresponding to a distance of , making this the first hydroxyl maser parallax below one milliarcsecond. We also introduce a new method of error analysis for detecting systematic errors in the astrometry. Finally, we compare our trigonometric distances to published phase-lag distances toward these stars and find a good agreement between the two methods.

AMMONIA AND CO OUTFLOW AROUND 6.7 GHz METHANOL MASERS

ABSTRACT Single point observations are presented in NH3 (1, 1) and (2, 2) inversion transitions using the Effelsberg 100 m telescope for a sample of 100 6.7 GHz methanol masers and mapping observations in the 12CO and 13CO (1 − 0) transitions using the Purple Mountain Observatory Delingha 13.7 m telescope for 82 sample sources with detected ammonia. A further 62 sources were selected for either 12CO or 13CO line outflow identification, producing 45 outflow candidates, 29 using 12CO and 16 using 13CO data. Twenty-two of the outflow candidates were newly identified, and 23 had trigonometric parallax distances. Physical properties were derived from ammonia lines and CO outflow parameters were calculated. Histograms and statistical correlations for ammonia, CO outflow parameters, and 6.7 GHz methanol maser luminosities are also presented. No significant correlation was found between ammonia and maser luminosity. However, weak correlations were found between outflow properties and maser luminosities, which may indicate that outflows are physically associated with 6.7 GHz masers.

The Milky Way without X: an alternative interpretation of the double red clump in the Galactic bulge

The presence of two red clumps (RCs) in high latitude fields of the Milky Way bulge is interpreted as evidence for an X-shaped structure originated from the bar instability. Here we show, however, that this double RC phenomenon is more likely to be another manifestation of multiple populations observed in globular clusters (GCs) in the metal-rich regime. As in the bulge GC Terzan 5, the helium enhanced second generation stars (G2) in the classical bulge component of the Milky Way are placed on the bright RC, which is about 0.5 mag brighter than the normal RC originated from the first generation stars (G1), producing the observed double RC. In a composite bulge, where a classical bulge can coexist with a boxy pseudo bulge, our models can also reproduce key observations, such as the dependence of the double RC feature on metallicity and Galactic latitude and longitude. If confirmed by Gaia trigonometric parallax distances, this would indicate that the Milky Way bar is not sufficiently buckled to form the X-shaped structure in the bulge, and suggest that the early-type galaxies would be similarly prevailed by super-helium-rich subpopulation.

The Lin–Shu type density wave structure of our Galaxy: line-of-sight velocities of 396 HII regions

In this fifth paper in a series, we check again the Lin–Shu idea of small-amplitude density waves in our Galaxy. The updated catalogue of Galactic objects of Hou and Han (Hou and Han in Astron Astrophys 569:125–146, 2014), available in the literature, is used. The line-of-sight velocity field of 396 HII regions with known trigonometric or photometric distances and their uncertainties within 4 kpc from the Sun is investigated in terms of a wave perturbation. Our previous study is enlarged by examining the secondary minima of the residual sum of squares of the predicted and measured velocities of a sample of objects in a considerable region surrounding the Sun. Both the geometrical and physical parameters of the wave pattern are evaluated. Here we show, for the first time, that the local Cygnus–Orion spiral arm, where the Sun is located, does form a part of the major density wave structure of the system under the question but is not a spur originating at the inner Carina–Sagittarius arm or at the outer Perseus arm.

THE SOLAR NEIGHBORHOOD. XXXV. DISTANCES TO 1404 M DWARF SYSTEMS WITHIN 25 PC IN THE SOUTHERN SKY

We present trigonometric, photometric, and photographic distances to 1748 southern ($\delta \leq$0$^\circ$) M dwarf systems with $\mu \ge$ 0\farcs18 yr$^{-1}$, of which 1404 are believed to lie within 25 parsecs of the Sun. The stars have 6.67 $\leq$ $V_J$ $\leq$ 21.38 and 3.50 $\leq$ ($V_J-K_s$) $\leq$ 9.27, covering the entire M dwarf spectral sequence from M0.0V through M9.5V. This sample therefore provides a comprehensive snapshot of our current knowledge of the southern sky for the nearest M dwarfs that dominate the stellar population of the Galaxy. Roughly one-third of the 1748 systems, each of which has an M dwarf primary, have published high quality parallaxes, including 179 from the RECONS astrometry program. For the remaining systems, we offer photometric distance estimates that have well-calibrated errors. The bulk of these ($\sim$700) are based on new $V_JR_{KC}I_{KC}$ photometry acquired at the CTIO/SMARTS 0.9m telescope, while the remaining 500 primaries have photographic plate distance estimates calculated using SuperCOSMOS $B_JR_{59F}I_{IVN}$ photometry. Confirmed and candidate subdwarfs in the sample have been identified, and a census of companions is included.

THE APPLICATION OF MULTIVIEW METHODS FOR HIGH-PRECISION ASTROMETRIC SPACE VLBI AT LOW FREQUENCIES

High precision astrometric Space Very Long Baseline Interferometry (S-VLBI) at the low end of the conventional frequency range, i.e. 20cm, is a requirement for a number of high priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in Pulsar--Black Hole pairs and OH masers anywhere in the Milky Way Galaxy and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8m in size and with ionospheric atmospheres consistant with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high quality orbit reconstruction of a space-based radio telescope. This will dramatically reduce the complexity of S-VLBI missions which implement the phase-referencing technique.

ANCHORING THE DISTANCE SCALE VIA X-RAY/INFRARED DATA FOR CEPHEID CLUSTERS: SU Cas

New X-ray (XMM-Newton) and JHKs (OMM) observations for members of the star cluster Alessi 95, which Turner et al.(2012) discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and 2MASS observations to determine precise cluster parameters: E(J-H)=0.08+-0.02 and d=405+-15 pc. The ensuing consensus among cluster, pulsation, IUE, and trigonometric distances (d=414+-5(se)+-10(sd) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (Delta Cep, Zeta Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H_0.

The age-metallicity relation in the thin disk of the galaxy

HST trigonometric distances, photometric metallicities, isochronic ages from the second revised version of the Geneva--Copenhagen survey, and uniform spectroscopic Fe and Mg abundances from our master catalog are used to construct and analyze the age--metallicity and age-relative Mg abundance relations for stars of the thin disk. The influences of selection effects are discussed in detail. It is demonstrated that the radial migration of stars does not lead to appreciable distortions in the age dependence of the metallicity. During the first several billion years of the formation of the thin disk, the interstellar material in this disk was, on average, fairly rich in heavy elements (<[Fe/H]> ~-0.2) and poorly mixed. However, the metallicity dispersion continuously decreased with age, from \sigma_{[Fe/H]}~0.22 to ~0.13. All this time, the mean relative abundance of Mg was somewhat higher than the solar value (<[Mg/Fe]>~0.1). Roughly four to five billion years ago, the mean metallicity began to systematically increase, while retaining the same dispersion; the mean relative Mg abundance began to decrease immediately following this. The number of stars in this subsystem increased sharply at the same time. These properties suggest that the star-formation rate was low in the initial stage of formation of the thin disk, but abruptly increased about four to five billion years ago.