LOW RESOLUTION SPECTROSCOPY OF WOLF-RAYET STARS
Jim Ferreira    Livermore CA    bakerst@comcast.net

Wolf-Rayet (WR) stars are the fascinating evolutionary result of hot, massive population 1, type O and early type B stars undergoing heavy mass loss due to intense solar wind.  Mass loss is on the order of a fraction of 1 solar mass per year, and stellar wind velocities as much as 2,000 kps -- comparable to velocities seen in a supernova!  The Wolf-Rayet progenitor stars are super-giants with masses greater than 100 solar masses.  Once stellar winds begin to peel away the outer atmosphere of the massive star, temperatures can rise to as much as 50,000K and luminosity on the order of 300,000 times that of the sun.

 

The broad emission line spectra of WR stars is evidence of the dense stellar wind that veils the underlying core of the star.  There is little indication of ionized hydrogen in the spectra, instead, highly ionized helium, nitrogen, oxygen and carbon dominate.

 

WR sub-classes are WN and WC, with a rare few in a WO sub-class.  The WN stars show strong lines of nitrogen and helium, and represent the earliest stage of WR evolution.  As helium combustion dominates in the core the star moves into the WC (WO) sub-class.  Interestingly, the WC (WO) sub-class is the hotter of WR stars, but significantly less luminous than WN stars.

 

As with other populations of stars, roughly half of the more than 200 known WR stars are part of binary or multiple star systems – some optically resolvable, others recognized only as spectroscopic pairs.  Several WRs are the core of planetary nebulae.  Most WR stars are variable, particularly the least evolved WRs, WN8 and WN7.  Variability is believed to be due to ‘clumps’ of mass in the stellar wind.  In the case of some binary systems, variability can be attributed to physical interaction between the associated stars.

 

A Wolf-Rayet star represents the most advanced stage in the very short life of a massive super-giant star, the next and final step is that of a type Ib or Ic super nova.

 ________________________________________________________

 

The following low resolution WR star spectra are a good sampling of both WN and WC type stars.  They show qualitatively how no two WR stars are the same, even within in the same sub-class.  Relative intensities of ionized He, N, O and C are seen to vary significantly between some stars.  Interestingly, the majority of these stars are found relatively close to each other in the constellations Cygnus, Perseus and Cassiopeia.


This is still very much a 'work in progress' so there will be periodic updates.  It is interesting how basic data varies between the catalogs and research journal papers.



All spectra were acquired with an 80mm f/6 APO refractor [Stellarvue SV80S], a Star Analyzer SA100 - 100 g/mm transmission grating and Atik ATK-16 CCD caemra.  The raw spectra are calibrated for wavelength, but no correction for instrument response was performed before normalizing the plots as my interest was to qualitatively show relative emission peak flux differences.  Spectra resolution ranging between approximately 50-80 Angstrom.  Calibration and plotting with RSpec spectral analyzing software.


Wolf-Rayet star spectra, WR154 WC6, Star Analyzer SA100
WR154 spectra image
CCD image of low resolution spectra produced with the Star Analyzer SA100 -- 10.94 magnitude Wolf-Rayet star WR154 is shown in the inverted gray scale 2D spectra inset

Wolf-Rayet star spectra, WN and WC spectral types
Wolf-Rayet WN-WC comparison
Above is a comparison of the raw 2-D spectra of WN and WC Wolf-Rayet stars
WN stars have prominent emission lines for N and He
WC stars have prominent emission lines for C and He



Principle Emission Lines
WN
wavelength

WC
wavelength
N III / He II
N III / He II
N III / He II
N III / He II
N V
N III
He II
Hb+He II
N V
N III
HeII
C IV
He I
4100
4210
4340
4541
4603-19
4634-41
4686
4860
4921
5314
5411
5808
5875
...........
C II
C III
C III
C III / C IV
He II
He I
C IV
O V
C III
C IV
He I
4267
4326
4540
4650
4686
5411
5471
5590
5696
5808
5876







WR star subclass, binary companions, V magnitudes and color indices quoted from VIIth Catalogue of Galactic Wolf-Rayet Stars (7Cat)

7Cat : http://grb.mmto.arizona.edu/~ggwilli/research/wr/docs/wr7.pdf



WN3

Wolf-Rayet star spectra WR127, Star Analyzer SA100
Wolf-Rayet WR127


WR127 is located in the constellation of Vulpecula.  A spectroscopic binary with a period of 9.55 days, there is no evidence of the O9.5 V companion star in this low resolution spectra.  B-V +0.21












WN4

Wolf-Rayet star spectra WR1, Star Analyzer SA100
WR1 WN4 Wolf-Rayet Star


WR1






Wolf-Rayet star spectra WR3, Star Analyzer SA100
WR3 WN4 Wolf-Rayet Star Spectra


WR3






Wolf-Rayet star spectra WR133, Star Analyzer SA100
Wolf-Rayet Star WR133 spectra


WR133 is a spectroscopic binary in the constellation of Cygnus.  7Cat lists WR133 as a WN4.5 + O9.5 1a binary with an orbital period of 112.7 days.  The O9.5 1a companion is a super-giant star.  The catalogue lists a photometric magnitude 7.48 V and color indice B-V +0.13.  WR133 is one of the central members of the open cluster NGC6871.






Wolf-Rayet star spectra WR157, Star Analyzer SA100
Wolf-Rayet Star WR157 spectra


WR157 at 10.13mV is a relatively inconspicuous member of open star cluster Ma 50 in Cepheus. 7Cat lists WR157 as a WN4.5 + B0 III visual binary with a 1.0" separation, the brighter component being the B0 III star.  Color index of the pair is B-V +0.52.












WN5
.....

Wolf-Rayet star spectra WR138, Star Analyzer SA100
Wolf-Rayet Star WR138 spectra


WR138 is in the constellation of Cygnus and is listed in 7Cat as a WN5+abs, which means it exhibits some atypical absorption lines suggesting it may have a companion.  V-B +0.26.






Wolf-Rayet star spectra WR139, Star Analyzer SA100
Wolf-Rayet Star WR139 spectra


WR139 is variable star V444 Cyg.  7Cat lists spectral type as WN5+06 III V, a binary with an orbital period of 4.21 days.  Color index B-V +0.38.






Wolf-Rayet star spectra WR141, Star Analyzer SA100
Wolf-Rayet Star WR141 spectra


WR141 is a questionable double with possibly an OB companion, several spectral types are given in the literature.  7Cat lists WR141 simply as a WN6.  The unidentified peak at ~6900 Angstrom is almost certainly a background star in my raw spectra.  Color index B-V +0.75.









Wolf-Rayet WR6, Alpy 600


WR6 is also cataloged as EZ Canis Majoris and is the brightest WR star easily visible in the northern hemisphere.  This spectra, unlike the others on this page was recorded with a 600 line/mm slit-spectrograph.  Compared to the similar WN5 spectra of WR141 (above), increase in spectral resolution is immediately apparent.









WN6


Wolf-Rayet star spectra WR134, Star Analyzer SA100
Wolf-Rayet Star WR134 spectra


WR134, also designated V1769 is variable in Cygnus with a magnitude range 7.8 - 7.93 V according to The International Variable Star Index.






Wolf-Rayet star spectra WR136, Star Analyzer SA100
Wolf-Rayet Star WR136 spectra
Wolf-Rayet star spectra WR136, Star Analyzer SA100
WR136 spectra
Wolf-Rayet star spectra WR136, Star Analyzer SA100
Wolf-Rayet WR136








WR136
WR136 / NGC6888 Crescent Nebula
WR136 is at the center of the NGC 6888

WR136 is better known as V1770 Cyg, the central star of NGC 6888, the 'Crescent Nebula.'  NGC 6888 had its beginning as a shell of gas thrown off by the solar wind when the star was a Red Giant several hundred thousand years ago.  What we see now is the high velocity solar wind of the now Wolf-Rayet star overtaking and interacting with the initial shell of gas in a most spectacular way. WR136 has a very compact companion, the two have an orbital period of 4.5 days and vary in brightness between 7.36 and 7.52 magnitude V.








Wolf-Rayet star spectra WR153, Star Analyzer SA100
Wolf-Rayet Star WR153 spectra


WR153, also known as CP Cephi, is a eclipsing binary system containing a WN6 Wolf-Rayet star and an O8-B0 III giant star.  According to the General Catalog of Variable Stars (GCVS) the pair is also associated with an spectroscopic pair of O type stars, or, possibly a single ellipsoidal star that varies in brightness over 3.47 days.  The WR and OB stars have their own orbital period of 6.69 days.  The whole system varies between 8.96-9.07 V magnitude.  Color index B-V +0.32.






AG Peg, Symbiotic Star, Wolf-Rayet WN6 spectra, Star Analyzer SA100
AG Peg, Symbiotic Star


AG Peg is a Z And symbiotic star system in the constellation of Pegasus.  AG Peg contains a WN6 Wolf-Rayet star and a M3 giant star, with an orbital period of 827 days.  AG Peg is referred to as a 'slow nova' -- in 1850 AG Peg began to brighten from ~9th magnitude to a peak outburst brightness of 6th magnitude in 1871.  It then took another century to fade to 8.5 magnitude.  Since then it has varied between 8.1 to 9.0 magnitude.












WN7


Wolf-Rayet star spectra WR155, Star Analyzer SA100
Wolf-Rayet Star WR155 spectra


WR155 is also cataloged as CQ Cep, a spectroscopic binary composed of a WN7 WR star and 09 giant or sub-giant star.  The pair has an orbital period of only 1.6 days and varies in brightness between 8.63 and 9.12 V magnitude.












WC5


Wolf-Rayet star spectra WR4, Star Analyzer SA100
WR4 WC5 Wolf-Rayet Star Spectra


WR4












WC6


Wolf-Rayet star spectra WR5, Star Analyzer SA100
Wolf-Rayet Star WR5 spectra


WR5  is a WC6 spectral type in the constellation of Perseus.  7Cat indicates that WR5 is a solitary star and 11.12 magnitude V.  Color index B-V +0.42.






Wolf-Rayet star spectra WR154, Star Analyzer SA100
Wolf-Rayet Star WR154 spectra


WR154 is located on the northern edge of the constellation Lacerta.  Visual magnitude 11.69 and B-V +0.31.












WC7


Wolf-Rayet star spectra WR137, Star Analyzer SA100
Wolf-Rayet Star WR137 spectra


WR137, V1679 Cyg is a binary system, its companion a 09 giant star.  The pair together vary irregularly in brightness between 7.89 and 7.93 V magnitude.  Some of the variation is theorized to result from optically thick clumps moving in the high speed solar wind.  Color index B-V +0.15.






Wolf-Rayet star spectra WR140, Star Analyzer SA100
Wolf-Rayet Star WR140 spectra


WR140 is a variable spectroscopic binary designated V1687 Cyg.  The binary is a WC7pd Wolf-Rayet star, its companion a 04 V main sequence star.  Interestingly the 6th Catalog of Galactic Wolf-Rayet Stars gives the spectral type WC7+abs which means a WC7 star that exhibits some absorption lines.  Unfortunately, low resolution spectra do not hint at the location of the absorption lines.












WC8


Wolf-Rayet star spectra WR135, Star Analyzer SA100
Wolf-Rayet Star WR135 spectra


WR135, V1042 Cyg is a WC8 spectral type Wolf-Rayet star.  The next step for this star is likely a short stint as a Luminous Blue Variable (LBV), or, a Super Nova Ib or Ic.  Compare the relative intensity of the C III and C IV peaks at 5696 and 5808 Angstrom respectively to those of the WC6 and WC7 stars.












Low resolution spectorscopy, Star Anayzer SA100 spectrograph, 80mm Stellarvue SV80S APO
SV80S, SA100 grating, monitors



Back to Spectroscopy