Perseus Arm Research Articles

Determining the Magnetic Field in the Galactic Plane from New Arecibo Pulsar Faraday Rotation Measurements

We develop a new method for studying the Galactic magnetic field along the spiral arms using pulsar Faraday rotation measures (RMs). Our new technique accounts for the dot-product nature of Faraday rotation and also splits the associated path integral into segments corresponding to particular zones along the line of sight. We apply this geometrically corrected, arm-by-arm technique to the low-latitude portion of a recently published set of Arecibo Faraday RMs for 313 pulsars, along with previously obtained RMs in the same regions. We find disparities >1σ between the magnitude of the field above and below the plane in the Local Arm, Sagittarius Arm, Sagittarius-to-Scutum Interarm, Scutum Arm, and Perseus Arm. We find evidence for a single field reversal near the Local Arm–Sagittarius Arm boundary. Interestingly, our results suggest that this field reversal is dependent on latitude, occurring inside the Sagittarius Arm at negative Galactic latitudes and at the Local Arm–Sagittarius Arm boundary at positive Galactic latitudes. We discuss all of our results in the context of different models and other observational Galactic magnetic field analyses.

Linear polarization study of open clusters in the anticenter direction: Signature of the spiral arms

Aims. Our objective is to investigate the distribution of dust and associated large-scale structures of the Galaxy using optical linear polarization measurements of various open clusters located at different distances in the Galactic anticenter direction. Methods. We present R-band linear polarization observations of stars toward five open clusters: Kronberger 1, Berkeley 69, Berkeley 71, Berkeley 19, and King 8 in the anticenter direction. The polarization observations were carried out using the ARIES (Aryabhatta Research Institute of Observational Sciences) IMaging POLarimeter mounted on the 104 cm Sampurnanand telescope of ARIES, Nainital, making it the first study to target the polarization observations toward distant clusters (~6 kpc). We combined the observed polarization data with the distance information from the Gaia space telescope to infer the dust distribution along the line of sight. Results. The variation in the degree of polarization and extinction with distance reveals multiple dust layers in each cluster direction. In addition, common foreground-dust layers detected toward different cluster directions highlight global features such as spiral arms. Our results show that the dust clouds at 2 kpc toward Berkeley 69 and Berkeley 71 coincide with the Perseus arm, while the dust layer at ~4 kpc toward the distant clusters Berkeley 19 and King 8 indicates the presence of the Outer arm. The large-scale dust distribution obtained by combining our polarization results with previous polarization studies of nearby open clusters suggests that the anticenter direction is characterized by a low-extinction homogeneous dust distribution with a somewhat uniform orientation of the plane-of-sky component of the magnetic field along the line of sight. Conclusions. Our study demonstrates that polarization is useful as a tool for studying the large-scale dust distribution and structural features where kinematic distance methods are inadequate and cannot provide accurate distances to the dust clouds. The global dust distribution in the anticenter direction shows signatures of the intervening spiral arms.

An in-depth analysis of the differentially expanding star cluster Stock 18 (Villafranca O-036) using Gaia DR3 and ground-based data

Context. The Villafranca project is combining Gaia data with ground-based surveys to analyze Galactic stellar groups (clusters, associations, or parts thereof) with OB stars. Aims. We want to analyze the poorly studied cluster Stock 18 within the Villafranca project, as it is a very young stellar cluster with a symmetrical and compact H II region around it, Sh 2-170, so it is likely to provide insights into the structure and dynamics of such objects at an early stage of their evolution. Methods. We used Gaia astrometry, photometry, spectrophotometry, and variability data as well as ground-based spectroscopy and imaging to determine the characteristics of Stock 18. We used these data to analyze its core, massive star population, extinction, distance, membership, internal dynamics, density profile, IMF, stellar variability, and Galactic location. Results. Stock 18 is a very young (∼1.0 Ma) cluster located at a distance of 2.91 ± 0.10 kpc and is dominated by the GLS 13 370 system, whose primary (Aa) is an O9 V star. We propose that Stock 18 was in a very compact state (∼0.1 pc) about 1.0 Ma ago and that most massive stars were ejected at that time without significantly affecting the less massive stars as a result of multi-body dynamical interactions. Different age estimates also point toward an age close to 1.0 Ma, indicating that the dynamical interactions took place very shortly after massive star formation. Well-defined expanding stellar clusters have been observed before, but none are as young as this one. If we include all of the stars, the initial mass function is top heavy, but if we discard the ejected ones, it becomes nearly canonical. Therefore, this is another example (in addition to the previous one we found – the Bermuda cluster) of (a) a very young cluster with an already evolved present day mass function (b) that has significantly contributed to the future population of free-floating compact objects. If confirmed in more clusters, the number of such compact objects may be higher in the Milky Way than previously thought. Stock 18 has a variable extinction with an average value of R5495 higher than the canonical one of 3.1. We have discovered a new visual component (Ab) in the GLS 13 370 system. The cluster is above our Galactic mid-plane, likely as a result of the Galactic warp, and it has a distinct motion with respect to its surrounding old population, which is possibly an influence of the Perseus spiral arm.

SRG/eROSITA 3D mapping of the interstellar medium using X-ray absorption spectroscopy

We present a detailed study of the hydrogen density distribution in the local interstellar medium (ISM) using the X-ray absorption technique. Hydrogen column densities were precisely measured by fitting X-ray spectra from coronal sources observed during the initial eROSITA all-sky survey (eRASS1). Accurate distance measurements were obtained through cross-matching Galactic sources with the third Gaia data release (DR3). Despite the absence of a discernible correlation between column densities and distances or Galactic longitude, a robust correlation with Galactic latitude was identified. This suggests a decrease in ISM material density in the vertical direction away from the Galactic plane. We have also investigated the relation between the optical extinction and the hydrogen column density. To do so, we employed multiple density laws to fit the measured column densities, revealing constraints on height scale values ($9 < h_ z < 14$ pc). Unfortunately, radial scales and the central density remain unconstrained due to the scarcity of sources near the Galactic center. Subsequently, a 3D density map of the ISM was computed using a Gaussian process approach, inferring hydrogen density distribution from hydrogen column densities. The results unveil the presence of multiple beams and clouds of various sizes, indicative of small-scale structures. High-density regions were identified at approximately 100 pc, consistent with findings in dust-reddening studies, and are potentially associated with the Galactic Perseus arm or the local bubble. Moreover, high-density regions were pinpointed in proximity to the Orion, Chameleon, and Coalsack molecular complex, enriching our understanding of the intricate structure of the local ISM.

Evolution of the Local Spiral Structure Revealed by OB-type Stars in Gaia DR3

The structure and evolution of the spiral arms of the Milky Way have long been an important yet controversial issue. The wide age range of OB-type stars, coupled with the large amount of high-precision astrometric data provided by Gaia DR3, presents us with an opportunity to explore this issue. After constructing overdensity maps and examining the variations of overdensities with Galactocentric distance along the Galactic azimuth, we compare the spiral structures traced by B3–B5, B6–B7, B8, and B9 stars with those of young O–B2 stars in the vicinity of the Sun. We find that as the ages of the OB tracer stars increase, the Perseus Arm traced by them gradually shifts toward the anti-Galactic center direction, and the pitch angle of the Carina Arm gradually decreases. These results will help us to understand better the evolutionary properties of nearby spiral arms.

On the Structure of the Sagittarius Spiral Arm in the Inner Milky Way

We report measurements of trigonometric parallax and proper motion for two 6.7 GHz methanol and two 22 GHz water masers located in the far portion of the Sagittarius spiral arm as part of the BeSSeL Survey. Distances for these sources are estimated from parallax measurements combined with three-dimensional kinematic distances. The distances of G033.64−00.22, G035.57−00.03, G041.15−00.20, and G043.89−00.78 are 9.9 ± 0.5, 10.2 ± 0.6, 7.6 ± 0.5, and 7.5 ± 0.3 kpc, respectively. Based on these measurements, we suggest that the Sagittarius arm segment beyond about 8 kpc from the Sun in the first Galactic quadrant should be adjusted radially outward relative to previous models. This supports the suggestion of Xu et al. that the Sagittarius and Perseus spiral arms might merge in the first quadrant before spiraling inward to the far end of the Galactic bar.

Distribution Properties of the 6.7 GHz Methanol Masers and Their Surrounding Gases in the Milky Way

An updated catalog consisting of 1092 6.7 GHz methanol maser sources is reported in this work. Additionally, the NH3 (1, 1), NH3 (2, 2), and NH3 (3, 3) transitions were observed toward 214 star-forming regions using the Shanghai Tianma radio telescope in order to examine the differences in physical environments, such as the excitation temperature and column density of molecular clouds associated with methanol masers on the Galactic scale. Statistical results reveal that the number of 6.7 GHz methanol masers in the Perseus arm is significantly lower than that in the other three main spiral arms. In addition, the Perseus arm also has the lowest gas column density among the main spiral arms traced by the NH3 observations. Both findings suggest that the Perseus arm has the lowest rate of high-mass star formation compared to the other three main spiral arms. We also observed a trend in which both the luminosity of the 6.7 GHz methanol masers and the ammonia gas column density decreased with the galactocentric distance. This finding indicates that the density of material in the inner Milky Way is generally higher than that in the outer Milky Way. This further suggests that high-mass stars are more easily formed at the head of the spiral arms. Furthermore, we found that the column density of ammonia gas is higher in the regions on the arms than in the inter-arm regions, supporting that the former is more likely to be the birthplace of high-mass stars.

Growing local arm inferred by the breathing motion

ABSTRACT Theoretical models of spiral arms suggest that the spiral arms provoke a vertical bulk motion in disc stars. By analysing the breathing motion, a coherent asymmetric vertical motion around the mid-plane of the Milky Way disc, with Gaia DR3, we found that a compressing breathing motion presents along the Local arm. On the other hand, with an N-body simulation of an isolated Milky Way-like disc galaxy, we found that the transient and dynamic spiral arms induce compressing breathing motions when the arms are in the growth phase, while the expanding breathing motion appears in the disruption phase. The observed clear alignment of the compressing breathing motion with the Local arm is similar to what is seen in the growth phase of the simulated spiral arms. Hence, we suggest that the Local arm’s compressing breathing motion can be explained by the Local arm being in the growth phase of a transient and dynamic spiral arm. We also identified the tentative signatures of the expanding breathing motion associated with the Perseus arm and also the Outer arm coinciding with the compressing breathing motion. This may infer that the Perseus and Outer arms are in the disruption and growth phases, respectively.

HIGH RESOLUTION OPTICAL SPECTRA OF THE DORMANT LBV STAR P Cyg

High resolution optical spectra (R = 60 000) of the dormant LBV star P Cyg were obtained on the BTA telescope in the wavelength range \(\Delta \lambda G7 = 780\) nm. After performing a detailed identification of different types lines (photospheric absorptions, permitted and forbidden emissions, components of lines with profiles of type P Cyg), we studied the variability of their profiles and patterns of radial velocities. The average radial velocity from positions of forbidden emissions ([N II] 5754.64, [Fe II] 5261.62, [Fe II] 7155.14 and [Ni II] 7377.83 Å) is accepted as the system \({{V}_{{{\text{sys}}}}} = - 34 \pm 1.4\) km/s. About a dozen photospheric absorptions of CNO-triad ions and Si III are found, their stable position, \({{V}_{r}}({\text{abs}}) = - 73.8\) km/s, shifted relative to \({{V}_{{{\text{sys}}}}}\) at \( - 40\) km/s, indicates that these absorbtions are formed in the pseudophotosphere region. The high-excitation emissions ([O I] 5577, 6300, 6363 Å, [O III] 4959 and 5007 Å, as well as He II 4686 Å) are absent in the spectra. The radial velocity \({{V}_{r}}({\text{DIBs}}) = - 11.8\) km/s according to the position of numerous DIBs is consistent with the position of the interstellar components of the D-lines Na I and K I forming in the galactic Perseus arm. An excess of color \(E(B - V) = 0.34 \pm {{0.03}^{m}}\) and interstellar absorption \({{A}_{v}}{{ = 1.09}^{m}}\) were determined by measurements of equivalent widths of nine DIBs.

G213.0−0.6, a true supernova remnant or just an H ii region?

Abstract G213.0−0.6 is a faint extended source situated in the anti-center region of the Galactic plane. It has been classified as a shell-type supernova remnant (SNR) based on its shell-like morphology, steep radio continuum spectrum, and high ratio of [H ii]/Hα. With new optical emission line data of Hα, [H ii], and [H ii] recently observed by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, the ratios of [H ii]/Hα and [H ii]/Hα are re-assessed. The lower values than those previously reported put G213.0−0.6 around the borderline of SNR-H ii region classification. We decompose the steep-spectrum synchrotron and the flat-spectrum thermal free-free emission in the area of G213.0−0.6 with multi-frequency radio continuum data. G213.0−0.6 is found to show a flat spectrum, in conflict with the properties of a shell-type SNR. Such a result is further confirmed by TT-plots made between the 863-MHz, 1.4-GHz, and 4.8-GHz data. Combining the evidence extracted in both optical and radio continuum, we argue that G213.0−0.6 is possibly not an SNR, but an H ii region instead. The VLSR pertaining to the Hα filaments places G213.0−0.6 approximately 1.9 kpc away in the Perseus Arm.

Exploring the structure and kinematics of the Milky Way through A stars

Context. Despite their relatively high intrinsic brightness and the fact that they are more numerous than younger OB stars and kinematically colder than older red giants, A-type stars have rarely been used as Galactic tracers. They may, in fact, be used to fill the age gap between these two tracers, thereby allowing us to evaluate the evolutionary and dynamic processes underlying the transition between them. Aims. We analyse Galactic disc structure and kinematic perturbations up to 6 kpc from the Sun based on observations of A-type stars. Methods. This work presents a catalogue of A-type stars selected using the IGAPS photometric survey. It covers the Galactic disc within 30° ≤l ≤ 215° and |b|≤5° up to a magnitude of r ≤ 19 mag with about 3.5 million sources. We used Gaia Data Release 3 parallaxes and proper motions, as well as the line-of-sight velocities, to analyse the large-scale features of the Galactic disc. We carried out a study of the completeness of the detected density distributions, along with a comparison between the b < 0° and b > 0° regions. Possible biases caused by interstellar extinction or by the usage of some kinematic approximations were examined as well. Results. We find stellar overdensities associated with the Local and the Perseus spiral arms, as well as with the Cygnus region. We find that A-type stars also provide kinematic indications of the Galactic warp towards the anticentre, which displays a median vertical motion of ∼6 − 7 km s−1 at a Galactocentric radius of R = 14 kpc. It starts at R ≈ 12 kpc, which supports the scenario where the warp begins at larger radii for younger tracers when compared with other samples in the literature. We also detect a region with downward mean motion extending beyond 2 kpc from the Sun towards 60° ≲l ≲ 75° that may be associated with a compression breathing mode. Furthermore, A-type stars reveal very clumpy inhomogeneities and asymmetries in the VZ − Vϕ velocity space plane.

Kinematics of the Local Spiral Structure Revealed by Young Stars in Gaia DR3

Using young open clusters and O–B2-type stars in Gaia Data Release 3, we investigate the kinematics of the local spiral structure. In general, the young sources in the outer spiral arms may present larger peculiar motions than those in the inner spiral arms. The young open clusters appear to have smaller peculiar motions than the O–B2-type stars, and the sources in both the Perseus and Local Arms may show an inward motion toward the Galactic center and rotate slower than Galactic rotation. Meanwhile, the sources in the Carina Arm may move in the opposite direction from the Sun to the Galactic center and rotate marginally faster than Galactic rotation. In addition, using young open clusters and O–B2-type stars, we have improved the distance estimations of kinematic methods for several regions near the Sun.

Distributions and Physical Properties of Molecular Clouds in the Third Galactic Quadrant: l = [219.°75, 229.°75] and b = [−5.°25, 5.°25

We present the results of an unbiased 12CO/13CO/C18O (J = 1–0) survey in a portion of the third Galactic quadrant (TGQ): 219.°75 ≤ l ≤ 229.°75 and −5.°25 ≤ b ≤ 5.°25. The high-resolution and high-sensitivity data sets help to unravel the distributions and physical properties of the molecular clouds (MCs) in the mapped area. In the LSR velocity range from ∼−1 to ∼85 km s−1, the molecular material successfully traces the Local, Perseus, and Outer arms. In the TGQ, the Outer arm appears to be more prominent than that in the second Galactic quadrant (SGQ), but the Perseus arm is not as conspicuous as that in the SGQ. A total of 1,502 12CO, 570 13CO, and 53 C18O molecular structures are identified, spanning over ∼2 and ∼6 orders of magnitude in size and mass, respectively. Tight mass–radius correlations and virial parameter–mass anticorrelations are observable. Yet, it seems that no clear correlations between velocity dispersion and effective radius can be found over the full dynamic range. The vertical distribution of the MCs renders evident pictures of the Galactic warp and flare.

Molecular Clouds in the Galactic Plane from l = [59.°75, 74.°75] and b = [−5.°25, +5.°25

In this paper we present the distribution of molecular gas in the Milky Way Galactic plane from l = [59.75, 74.75]° and b = [−5.25, +5.25]°, using the MWISP 12CO/13CO/C18O emission-line data. The molecular gas in this region can be mainly attributed to the Local Spur, Local Arm, Perseus arm, and Outer arm. Statistics of the physical properties of the molecular gas in each arm, such as excitation temperature, optical depth, and column density, are presented. Using the DBSCAN algorithm, we identified 15 extremely distant molecular clouds with kinematic distances of 14.72−17.77 kpc and masses of 363−520 M ⊙, which we find could be part of the Outer Scutum–Centaurus (OSC) arm identified by Dame & Thaddeus and Sun et al. It is also possible that 12 of these 15 extremely distant molecular clouds constitute an independent structure between the Outer and the OSC arms or a spur. Two Gaussian components exist in the vertical distribution of the molecular gas in the Perseus spiral arm. These two Gaussian components correspond to two giant filaments parallel to the Galactic plane. We find an upward warping of the molecular gas in the Outer spiral arm with a displacement of around 270 pc with respect to the Galactic midplane.

Distance of PSR B0458+46 indicated by FAST H i absorption observations

ABSTRACT The pulsar B0458+46 was previously believed to have a distance of about 1.3 kpc and to be associated with a nearby supernova remnant, SNR HB9 (G160.9+2.6). We observe the neutral hydrogen (H i) absorption spectrum of PSR B0458+46 by using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and detect two absorption lines at radial velocities of VLSR = −7.7 and −28.1 km s−1. Based on the Galactic rotation curve with a modification factor correcting for the systematic stream in the Galactic anticentre region, we derive the kinematic distance of the farther absorption cloud, which is found to be located $2.7^{+0.9}_{-0.8}$ kpc away, just beyond the Perseus Arm. We also obtain a direct distance estimation of the farther absorption cloud as being $2.3_{-0.7}^{+1.1}$ kpc, based on a comparison of the velocity with the H i emission in the Perseus and Outer Arms that was well-defined by recently measured parallax tracers. As a result, we conclude that PSR B0458+46 should be located beyond the Perseus Arm, with a lower limit for the distance at 2.7 kpc, and therefore not associated with SNR HB9. The doubled distance indicates a deficiency of thermal electrons in the immediate outer Galaxy, with a much less density than current models predict. Additionally, we detect a new high-velocity H i cloud in the direction of this pulsar.

Gaia Data Release 3

Context. With the most recent Gaia data release, the number of sources with complete 6D phase space information (position and velocity) has increased to well over 33 million stars, while stellar astrophysical parameters are provided for more than 470 million sources, and more than 11 million variable stars are identified. Aims. Using the astrophysical parameters and variability classifications provided in Gaia DR3, we selected various stellar populations to explore and identify non-axisymmetric features in the disc of the Milky Way in configuration and velocity space. Methods. Using more about 580 000 sources identified as hot OB stars, together with 988 known open clusters younger than 100 Myr, we mapped the spiral structure associated with star formation 4−5 kpc from the Sun. We selected over 2800 Classical Cepheids younger than 200 Myr that show spiral features extending as far as 10 kpc from the Sun in the outer disc. We also identified more than 8.7 million sources on the red giant branch (RGB), of which 5.7 million have line-of-sight velocities. This later sample allows the velocity field of the Milky Way to be mapped as far as 8 kpc from the Sun, including the inner disc. Results. The spiral structure revealed by the young populations is consistent with recent results using Gaia EDR3 astrometry and source lists based on near-infrared photometry, showing the Local (Orion) Arm to be at least 8 kpc long, and an outer arm consistent with what is seen in HI surveys, which seems to be a continuation of the Perseus arm into the third quadrant. The subset of RGB stars with velocities clearly reveals the large-scale kinematic signature of the bar in the inner disc, as well as evidence of streaming motions in the outer disc that might be associated with spiral arms or bar resonances. A local comparison of the velocity field of the OB stars reveals similarities and differences with the RGB sample. Conclusions. This cursory study of Gaia DR3 data shows there is a rich bounty of kinematic information to be explored more deeply, which will undoubtedly lead us to a clearer understanding of the dynamical nature of the non-axisymmetric structures of the Milky Way.

Mapping the distribution of OB stars and associations in Auriga

ABSTRACT OB associations are important probes of recent star formation and Galactic structure. In this study, we focus on the Auriga constellation, an important region of star formation due to its numerous young stars, star-forming regions, and open clusters. We show using Gaia data that its two previously documented OB associations, Aur OB1 and OB2, are too extended in proper motion and distance to be genuine associations, encouraging us to revisit the census of OB associations in Auriga with modern techniques. We identify 5617 candidate OB stars across the region using photometry, astrometry and our SED fitting code, grouping these into five high-confidence OB associations using HDBSCAN. Three of these are replacements to the historical pair of associations – Aur OB2 is divided between a foreground and a background association – while the other two associations are completely new. We connect these OB associations to the surrounding open clusters and star-forming regions, analyse them physically and kinematically, constraining their ages through a combination of 3D kinematic traceback, the position of their members in the HR diagram and their connection to clusters of known age. Four of these OB associations are expanding, with kinematic ages up to a few tens of Myr. Finally, we identify an age gradient in the region spanning several associations that coincides with the motion of the Perseus spiral arm over the last ∼20 Myr across the field of view.

Astrometric VLBI observations of H2O masers in an extreme OH/IR star candidate NSV 17351

Abstract The results of astrometric very long baseline interferometry (VLBI) observations toward an extreme OH/IR star candidate NSV 17351 are presented. Using the VERA (VLBI Exploration of Radio Astrometry) VLBI array , we observed 22 GHz H2O masers of NSV 17351 and derived an annual parallax of 0.247 ± 0.035 mas, which corresponds to a distance of 4.05 ± 0.59 kpc, from the observation. By averaging proper motions of 15 maser spots further, we determined the systemic proper motion of NSV 17351 to be (μαcos δ, μδ)avg. = (−1.19 ± 0.11, 1.30 ± 0.19) mas yr−1. The maser spots spread out over a region of 20 × 30 mas, which can be converted to a spatial distribution of ∼80 × 120 au at the source distance. Internal motions of the maser spots suggest an outward-moving maser region with respect to the estimated position of the central star. From single-dish monitoring of the H2O maser emission, we estimate the pulsation period of NSV 17351 to be 1122 ± 24 d. This is the first report of the periodic activity of NSV 17351, indicating that NSV 17351 could have a mass of ∼4 M⊙. We confirmed that the time variation of H2O masers can be used as a period estimator of variable OH/IR stars. Furthermore, by inspecting dozens of double-peaked H2O maser spectra for the last 40 years, we discovered the long-term acceleration in the radial velocity of the circumstellar matter to be 0.17 ± 0.03 km s−1 yr−1. We finally determined the position and kinematics in the Milky Way Galaxy and found that NSV 17351 is located in an interarm region between the Outer and Perseus arms. We note that the astrometric VLBI observation toward extreme OH/IR stars shows us a useful sample of the Galactic dynamics.

What Does the Milky Way Look Like?

In spite of much work, the overall spiral structure morphology of the Milky Way remains somewhat uncertain. In the last two decades, accurate distance measurements have provided us with an opportunity to solve this issue. Using the precise locations of very young objects, for the first time, we propose that our galaxy has a multiple-arm morphology that consists of two-arm symmetry (the Perseus and Norma Arms) in the inner parts and that extends to the outer parts, where there are several long, irregular arms (the Centaurus, Sagittarius, Carina, Outer, and Local Arms).

Determination of the Spiral Pattern Speed in the Galaxy from Three Samples of Stars

We invoke the estimates of the amplitudes of the velocity perturbations $f_R$ and $f_\theta$ caused by the influence of a spiral density wave that have been obtained by us previously from three stellar samples. These include Galactic masers with measured VLBI trigonometric parallaxes and proper motions, OB2 stars, and Cepheids. From these data we have obtained new estimates of the spiral pattern speed in the Galaxy $\Omega_p:$ $24.61\pm2.06$, $24.71\pm1.29$ and $25.98\pm1.37$~km s$^{-1}$ kpc$^{-1}$ from the samples of masers, OB2 stars, and Cepheids, respectively. The corotation radii for these three samples $R_{\rm cor}/R_0$ are $1.16\pm0.09$, $1.15\pm0.06$ and $1.09\pm0.06,$ suggesting that the corotation circle is located between the Sun and the Perseus arm segment.