Star In Cygnus Research Articles

Large-scale expansion of OB stars in Cygnus

ABSTRACT The proper motions (PMs) of OB stars in Cygnus have recently been found to exhibit two large-scale kinematic patterns suggestive of expansion. We perform a 3D traceback on these OB stars, the newly identified OB associations and related open clusters in the region. We find that there are two groups of stars, associations and clusters and that they were each more compact in the past, reaching their closest approach $7.9^{+3.0}_{-1.8}$ and $8.5^{+0.8}_{-2.8}$ Myr ago. We consider two main scenarios for the driver of these large-scale expansion patterns: feedback-driven expansion from a previous generation of massive stars, and expansion as a result of the turbulent velocity field in the primordial molecular cloud. While it is tempting to attribute such large-scale expansion patterns to feedback processes, we find that the observed kinematics are fully consistent with the turbulent origin, and therefore that the injection of further energy or momentum from feedback is not required. Similar conclusions may be drawn for other star forming regions with large-scale expansion patterns.

Interstellar Highly Ionized Species toward Cygnus: A Closer Look

Abstract We examine Hubble Space Telescope (HST)/STIS data, complemented with International Ultraviolet Explorer (IUE) data, to delineate interstellar absorption of highly ionized species, C iv, Si iv, and N v, and low ionization species toward four stars in Cygnus. Previous IUE studies indicate two major velocity complexes for C iv and Si iv extending across Cygnus. We see interstellar N v in HST/STIS data for HD 190918 and Cyg X-1. In both stars, the N v is at the velocities of interstellar C iv and Si iv. In HD 190918, the N v is weak, possibly due to enhanced X-ray ionization produced by this binary system. The Cyg X-1 data are of low signal-to-noise, but N v is quite strong with a small b-value, indicating N v arises in a cooler H ii region resulting from X-ray Auger ionization by Cyg X-1.

V2492 Cygni: THE EARLY EVOLUTION OF THE 2010 OUTBURST

We present Gemini-North optical and near-IR observations of a young eruptive star in Cygnus, designated as V2492 Cyg in the General Catalog of Variable Stars. This object is one of two young stars, located within 2 degrees of each other, that recently brightened by around 5 mags and were reported as possible new FU Orionis-type variables. The outburst spectrum of V2492 Cyg shows atomic emission features throughout the optical and near-infrared. In the optical, Halpha is in emission and has an associated blue-shifted absorption component. The far-red CaII triplet lines are also in emission and, as with Halpha, possess significant blue-shifted absorption. The optical TiO molecular bands are also in emission. In the near-infrared, Pabeta, Brgamma, and the CO overtone bandheads are strongly in emission. Such spectral characteristics are very similar to those exhibited by both EX Lupi, the progenitor of the EXor class of eruptive variables, during its 2008 extreme outburst, and V1647 Ori during its elevated phase in 2003. Additionally, we consider archival data on V2492 Cyg and investigate the pre-outburst nature of this young star. We construct a quiescent-phase spectral energy distribution which, via model fitting, gives insight into the circumstellar environment of the object prior to the current eruption. Our investigation strongly suggests that the V2492 Cyg outburst appears to be more consistent with an EXor event, a fact supported by its recent 2 mag fading and stochastic variability.

Near-Infrared Colors of Carbon Stars in Cygnus

Abstract The J-H, H-K diagram based on the 2MASS Sky Survey for 140 carbon stars in Cygnus, which have been photometrically monitored with the Baldone Schmidt telescope, is discussed.

Long-Term Photometric Behavior of 18 Carbon Stars in Cygnus

Abstract The large variety of long-term (secondary) variations is demonstrated on the basis of a 30 year long photographic red magnitude time-series for 18 carbon stars in Cygnus based on the observations carried out with the Baldone Schmidt telescope.

Gamma-rays from massive stars in Cygnus and Orion

Radioactive 26Al, ejected by massive stars through winds and supernova explosions, leads to γ-ray line emission that can serve as a probe of the interstellar environment in and near young star clusters. The ~ 1 Myr decay time of 26Al is long enough to allow transport over significant distances, which can cause substantial angular offsets between γ-ray emission and cluster stars. Details of such offsets are determined by the morphology of the ISM. We discuss observations in Cygnus and Orion, and models based on population synthesis methods.

Temperature Profiles of Accretion Disks around Rapidly Rotating Neutron Stars in General Relativity and the Implications for Cygnus X‐2

We calculate the temperature profiles of (thin) accretion disks around rapidly rotating neutron stars (with low surface magnetic fields), taking into account the full effects of general relativity. We then consider a model for the spectrum of the X-ray emission from the disk that is parameterized by the mass accretion rate, the color temperature, and the rotation rate of the neutron star. We derive constraints on these parameters for the X-ray source Cygnus X-2 using the estimates of the maximum temperature in the disk along with the disk and boundary layer luminosities, using the spectrum inferred from the EXOSAT data. Our calculations suggest that the neutron star in Cygnus X-2 rotates close to the centrifugal mass-shed limit. Possible constraints on the neutron star equation of state are also discussed.

Cygnus X-2, super-Eddington mass transfer, and pulsar binaries

We consider the unusual evolutionary state of the secondary star in Cygnus X-2. Spectroscopic data give a low mass ($M_2 \simeq 0.5 - 0.7\msun$) and yet a large radius ($R_2 \simeq 7\rsun$) and high luminosity ($L_2 \simeq 150\lsun$). We show that this star closely resembles a remnant of early massive Case B evolution, during which the neutron star ejected most of the $\sim 3\msun$ transferred from the donor (initial mass $M_{\rm 2i}\sim 3.6\msun$) on its thermal time-scale $\sim 10^6$ yr. As the system is far too wide to result from common-envelope evolution, this strongly supports the idea that a neutron star efficiently ejects the excess inflow during super--Eddington mass transfer. Cygnus X-2 is unusual in having had an initial mass ratio $q_{\rm i} = M_{\rm 2i}/M_1$ in a narrow critical range near $q_{\rm i}\simeq 2.6$. Smaller $q_{\rm i}$ lead to long-period systems with the former donor near the Hayashi line, and larger $q_{\rm i}$ to pulsar binaries with shorter periods and relatively massive white dwarf companions. The latter naturally explain the surprisingly large companion masses in several millisecond pulsar binaries. Systems like Cygnus X-2 may thus be an important channel for forming pulsar binaries.

New periods of variable stars in Cygnus based on a quarter of century of photographic observations

This work summarizes the results of photo- graphic photometry obtained over 24 years at the Skalnat e Pleso (1979-1993) and Asiago (1969-1988) observatories. The period of light changes, the epoch of the maximum or of the minimum, the type of variability and, in some cases, possible causes of the long-term behaviour of light changes were determined for 17 variable stars.

RED SPECTRA OF THE BRIGHTEST STARS IN CYGNUS OB2: POSSIBLE DETECTION OF TWO NEW INTERSTELLAR BANDS

ABSTRACT The stellar and interstellar spectra of the 12 brightest stars in the Cygnus OB2 association are described. The observations were made in the wavelength range 5800 A-8500 A, at about 7 A resolution. Two new lines, centered near 7430 A and 7932 A, may be previously undetected interstellar bands. The former may be formed in the interstellar medium as well as in the dust environment of Cyg OB2, while the latter may be formed only in the dust environment of Cyg OB2.

Polarization variability among Wolf-Rayet stars. V - Linear polarization of the bright Cygnus stars and an anticorrelation of variability with wind speed

This paper presents polarimetric data for seven of the eight bright WR stars in Cygnus. Six of the stars show only random, low-amplitude modulation on time scales of hours to days. One of these behaves as expected for a long-period WR + O system with an elliptical orbit. The eighth star is the only short-period WR + O binary in the sample. It is confirmed that the degree of random, intrinsic scatter in polarization is correlated with spectral subclass and terminal wind velocity. It is suggested that this is caused by the presence of propagating blobs which form, survive, and/or grow more easily in slower winds. Two models are proposed to explain the origin of the blobs. 93 refs.

MK classifications of stars in Cygnus

MK spectral classifications are given for 24 stars of types B and A in Fehrenbach's selected area No.4 ( l = 73, 94°, b = +1.07°) for radial velocity investigations. The spectroscopic observations were made with the Marly spectrograph at the 120 cm telescope of Haute Provence Observatory. A spectral atlas of the standard stars is given, and the main criteria for classification are described. Many of the target stars have broad lines and one of them, HD 192605 is especially interesting, having a large Balmer progression of radial velocity.

On Wolf-Rayet stars with unshifted absorption lines

view Abstract Citations (47) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On Wolf-Rayet stars with unshifted absorption lines. Moffat, A. F. J. ; Lamontagne, R. ; Shara, M. M. ; McAlister, H. A. Abstract The authors examine a sample of 16 galactic Wolf-Rayet stars that exhibit unshifted absorption lines, but for which orbital motion involving the WR star and an O-type companion is either unknown or thought to be absent. If all of these are binaries, this would increase the estimate of the binary frequency for WR stars by about 10%. Speckle interferometry of three bright non-WNL+abs stars in Cygnus fails to reveal any astrometric companions down to a separation of 0.05arcsec. Thus, either the absorption lines are intrinsic to the WR star in these three cases or, more likely, they arise in a bound companion. The search for wide spectroscopic orbits for WR 137 and the WN3+abs star WR 3 is re-examined. Publication: The Astronomical Journal Pub Date: June 1986 DOI: 10.1086/114116 Bibcode: 1986AJ.....91.1392M Keywords: Absorption Spectra; Companion Stars; O Stars; Stellar Orbits; Stellar Spectra; Wolf-Rayet Stars; Balmer Series; Interferometry; Radial Velocity; Speckle Patterns; Astrophysics full text sources ADS | data products SIMBAD (15)

The radio sources and their exciting stars in Cygnus X

Physical parameters (density, mass of the ionized gas, emission measure, excitation parameter) of various thermal sources of the Cygnus X complex were derived by adopting a simple spherical model. The limitations of the excitation parameter-spectral class relationship are discussed and because of them no reliable conclusion can be drawn about the nature of their exciting stars. Physical characteristics of two non-thermal sources were also derived on the assumption they are SNR.

On the Chemical Composition of Wolf-Rayet Stars

The chemical composition of 5 WR stars in Cygnus are considered by using the quasi-nebular variant of Beals' model. On the basis of the general considerations which follow from this model it was concluded that the C/He ratio for the WC stars appears to be more than 10 times higher than for normal OB stars and the N/He ratio in the case of the WN stars seems also to be somewhat higher than for normal OB stars. From the solution of the equations of statistical equilibrium for the level populations, it was found that in the case of the WC stars C/He≈1 and in the case of the WN stars N/He≈0.05–0.1. For the star HD 192163 (WN6) it was found that He/H≈4.2–7.3 and for the other stars He/H≳10.

The Colors of M Supergiants

view Abstract Citations (52) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Colors of M Supergiants Johnson, Harold. L. Abstract The available infrared photometric data for M supergiant stars are re-examined. It is possible to explain part of the large infrared excesses of reddened M supergiant stars as intrinsic stellar radiation; a part must still be explained in terms of interstellar extinction. If the spectral type of the NeugebauerMartx-Leighton infrared star in Cygnus is M6 Ia, it has very large infrared excesses that appear to be reasonable compared with those found for other M supergiants. Under this interpretation, its color excess in B - V is approximately 3 mag. Publication: The Astrophysical Journal Pub Date: August 1967 DOI: 10.1086/149257 Bibcode: 1967ApJ...149..345J full text sources ADS | data products SIMBAD (27) GCPD (1)

The Infrared Polarization of the Infrared Star in Cygnus

Wavelength dependence of polarization of IR star in Cygnus measured by far IR lead sulfide photopolarimeter

Multicolor Photometry of Northern Wolf-Rayet Stars

view Abstract Citations (46) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multicolor photometry of Northern Wolf-Rayet stars. Westerlund, B. E. Abstract Thirty-five objects listed by Roberts as Wolf-Rayet stars have been observed photoelectrically in a narrow-band four-color system. The system is calibrated through observations of six spectrophotometric standard stars. Comparisons with the UB V system are presented. Criteria for separating single W-R stars from binaries as well as WC stars from WN stars are investigated. The distances of the W-R stars in Cygnus are discussed briefly. Publication: The Astrophysical Journal Pub Date: September 1966 DOI: 10.1086/148819 Bibcode: 1966ApJ...145..724W full text sources ADS | data products SIMBAD (36) GCPD (1)

A Peculiar Emission Star in Cygnus, MHα 328-116

view Abstract Citations (55) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Peculiar Emission Star in Cygnus, MHα 328-116 Fitzgerald, M. P. ; Houk, Nancy ; McCuskey, S. W. ; Hoffleit, Dorrit Abstract Preliminary identification of seventy-seven emission lines in the spectrum of MHa 328-116 is given. The spectrum appears to be similar to that of a symbiotic variable. The emission lines are relatively sharp indicating a low-expansion velocity for the gaseous shell producing them. Only two very weak absorption lines are visible on our spectra (130 A/mm dispersion). The star has increased in brightness from 15.5 to 11.5 mag. since 1963. A light-curve for the period 1920-1965 is given. Publication: The Astrophysical Journal Pub Date: June 1966 DOI: 10.1086/148707 Bibcode: 1966ApJ...144.1135F full text sources ADS | data products SIMBAD (9)

Slopes of the Reddening Trajectories and Intrinsic Colors of Early-Type Stars.

view Abstract Citations (76) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Slopes of the Reddening Trajectories and Intrinsic Colors of Early-Type Stars. Serkowski, K. Abstract The UB V observations of early-type stars show that the slope of the reddening trajectory is independent of the ratio of polarization to interstellar reddening. This proves that the alignment of inter- stellar dust grains cannot be responsible for suggested regional variations in the law of reddening. For the early-type stars in Cygnus the deviations of U - B colors from the reddening trajectory defined by stars from other galactic longitudes are positive and independent of the amount of polarization; they indicate that / is larger by 0.05 in Cygnus than elsewhere. Improved intrinsic colors of early-type stars and a nomogram for computation of intrinsic B - V colors from UB V photometry of main-sequence B-type stars are given. Publication: The Astrophysical Journal Pub Date: November 1963 DOI: 10.1086/147704 Bibcode: 1963ApJ...138.1035S full text sources ADS | data products SIMBAD (25)