Be Star Spectroscopy Using the UCA Fiber-Fed Spectrograph Scott Austin University of Central Arkansas

Journal of the Arkansas Academy of Science

Volume 58 Article 5

2004 Be Star Spectroscopy Using the UCA Fiber-Fed Spectrograph Scott Austin University of Central Arkansas

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Recommended Citation Austin, Scott (2004) "Be Star Spectroscopy Using the UCA Fiber-Fed Spectrograph," Journal of the Arkansas Academy of Science: Vol. 58 , Article 5. Available at: http://scholarworks.uark.edu/jaas/vol58/iss1/5

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Be Star Spectroscopy Using the UCA Fiber-Fed Spectrograph

Scott Austin Department of Physics and Astronomy University of Central Arkansas Conway, AR 72035

Abstract

Beginning inJune 2003, undergraduate students and the author have spectroscopically monitored bright Be stars using a custom built fiber-fed spectrograph attached to the UCA Observatory 11-inch Schmidt- Cassegrain telescope. We have obtained 0.8 Angstrom/pixel resolution spectra of the H-alpha line for over forty Be-Stars. Some have been observed on multiple dates in order to detect any temporal changes. Line profiles, velocities, and observed variations for some of these stars willbe presented.

Introduction us to studying relatively bright objects. The observatory facilities consist of a five m dome and Be stars are spectral type B non-supergiant stars whose a Celestron 11-inch (0.28 m) aperture f/10 Schmidt- Balmer lines have been observed to have been in emission Cassegrain telescope (Cll). The 11-inch aperture is another at some time (Jaschek et al., 1981). Emission lines indicate factor in limiting us to bright objects. The equatorial fork the presence ofcircumstellar gas that has been photoionized mount of the telescope has been retrofitted with digital by the star. The line profile of the Balmer lines (e.g., H- setting circles, which greatly improve the pointing precision alpha) offers clues to the shape, orientation, and speed and accuracy. Mounted on the Cll is a Meade ETX (expansion and rotation) of the flattened circumstellar telescope with aMeade 216XT CCD camera, which is used envelope. Be stars exhibit a variety of line profiles. In for guiding while taking exposures with the Cll. addition, the line profiles of many Be stars change over time. Fiber-Fed Spectrograph.-- A telescope the size of the Cll For some Be stars, the circumstellar envelopes dissipate and is restricted in the size and weight of instrumentation that reform. The stellar absorption lines of these stars show that can be mounted inits focal plane. This was the motivation these are rapidly rotating stars. for building a spectrograph system using a bench Possible mechanisms that may contribute to the spectrograph and optical fibers to transport light from the formation of the circumstellar disks include rapid rotation focal plane of the telescope to the spectrograph. In this case, (Cranmer and Owocki, 1996), stellar winds (Dessart and only a relatively small and lightweight assembly has to be Owocki 2003), magnetism (Poe and Friend, 1986), non- mounted to the telescope. The fiber/coupler assembly radial stellar pulsations (Maintz et al., 2003), and binary holds the ends of the fibers in the focal plane and contains companions (Apparao, 2002). The mechanism for forming optics and video used to acquire stars onto the fibers. The these disks is not wellunderstood, nor is itclear what causes design of our system is based mostly upon that built at some Be stars to dissipate and reform their circumstellar Harvard (Kannappan and Fabricant, 2000; Kannappan et disks. al., 2002). Their system required using an eyepiece for Observations are needed to test the models for these target acquisition and guiding; our system has a video stars. We and other Be star observers around the world are camera system we have incorporated into the attempting tobuild up a sufficient database of the temporal- guider/coupler assembly. spectral-variations for as many different Be stars as possible. Three 100-micron diameter optical fibers are used to There are over 100 Be stars brighter than 6th magnitude that transport light from the telescope to the bench spectrograph. are visible during the year from our latitude. The work One fiber is used to obtain starlight and the other two are here represents part of the first several months of able to monitor any sky background. Experience shows that our observational work toward this goal. thus far sky background is below any significant detectable limits. Therefore, sky subtraction has not been necessary. Materials and Methods The bench spectrograph consists of a fiber holder, collimating lens, reflection diffraction grating with 1800 Observatory.-The UCA observatory is atop lines/mm, 50mm camera lens, and a Finger Lakes MaxCam LUCAwis Science Center on the UCA campus. The UCA CCD camera. This results in0.8 Angstrom/pixel resolution campus is located in Conway Arkansas, population ca. near H-alpha with 675 Angstrom coverage. 45,000. Given the urban location, light pollution is a Data Acquisition.~The CCD camera for the bench significant problem. This is one of the factors that restricts spectrograph is controlled with a laptop computer running

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Be Star Spectroscopy Using the UCA Fiber-Fed Spectrograph

MaxIM/DL. The images are saved in Flexible Image of these ten stars are relative to the continuum level (I/Ic) Transport System (FITS) format. Multiple zero-second and have not been smoothed. exposure bias frames were acquired at the beginning of the The 48 Librae profiles obtained on 22 and 27June 2003 night. Next, a spectrum of a mercury-neon lamp was June are shown in Fig. 1. The two profiles are identical, acquired at the beginning of the night for the purpose of demonstrating no significant changes over five days. This wavelength calibration. Since the spectrograph is a bench- star is known tobe a spectroscopic variable over longer time spectrograph and is housed in a cabinet where there is little periods (Aydin and Faragiana, 1978). Both profiles are change in temperature during the night, the wavelength asymmetric and double peaked, with the blue side weaker calibration is stable. Next, a spectrum of a bright than the red side of the profile, similar to that reported by spectroscopic standard star was obtained for the purpose of Banerjee, Rawat, and Janardhan (2000). The FWHM relative flux calibration. Once these calibration frames were velocity of the profile is about 570+63 km/sec. obtained for the night, spectra of Be stars brighter than 7th Delta Scorpii became a Be star in the year 2000 magnitude near the meridian were acquired. To get an (Fabregat and Reig, 2000). Shown in Fig. 2 are profiles adequate signal-to-noise-ratio (SNR), exposures ranged obtained on four nights inJune and July 2003. The profiles from 10 to 45 minutes. To make fine guiding corrections to show a single peak with FWHM velocity of 337±63 km/sec. ensure that the light from the target star travels down the The profiles did not show any significant changes over the fiber, the observer must watch the video output from the month of observations. guider/coupler and make necessary adjustments with the Chi Ophiuchi was observed six times between 12 June Cll control paddle. 2003 and 23 July 2003. The line profiles are shown for four Data Reduction.~The raw FITS frames are transferred of the dates in Fig. 3. The single peaked line profile peak to a LINUXworkstation running Interactive Reduction and I/Ic intensity varied between 6.1±0.1and 7.6±0.1. The Analysis Facility (IRAF). The FITS frames are exported to FWHM velocity varied between 284±63 km/sec and tRAF format. The zero-second bias frames are combined to 300±63 km/sec. The profile from 15 March 1999 reported form a master bias frame. This master bias frame is then by Banerjee, Rawat, and Janardhan (2000) showed a single subtracted from the raw spectral frames. The two- peak with a slight red shoulder and I/Icof about 11.5. dimensional spectra are extracted and summed from each of Observations of Omicron Herculis from 12 June 2003 these frames, producing one-dimensional spectra. The lines and 31July 2003 are shown in Fig. 4; they show a weak in the mercury-neon lamp spectrum are then identified, and emission feature with a FWHM velocity of 280±63 km/sec a wavelength as a function of pixel number solution is fit. within a broad absorption feature. The stellar spectra are then wavelength calibrated with this 4 Aquilae was observed on 20 June 2003 and 8 July solution. The spectra of the spectral standard stars are used 2003. The single peak profiles (Fig. 5) withFWHM velocity to relative-flux calibrate the spectra of the Be stars. A of about 450+63 km/sec are within a broad absorption spectral response function is determined by comparing the feature. The I/Icintensity may have changed slightly. observed standard star spectrum with the known flux per Fig. 6 shows the line profiles of V923 Aquilae from 27 Dandpass. To relative-flux calibrate the spectra of the Be June 2003 and 24 July 2003. The profiles from these two stars, this response function is applied. Finally, the Be star dates are nearly identical, and have a double peak spectra are normalized to the continuum level of the spectra. asymmetric profile. The blue side of the profile is weaker This allows us to compare H-alpha line profiles of the same than the red side. The FWHM velocity is about 235±63 star on different dates. km/sec. Data Analysis.--IBAF is used to measure the physical The profiles of Beta^ Cygni are shown in Fig. 7. The )arameters of the H-alpha line profiles of the Be stars, observations were recorded on 22 June 2003 and 24 July "hese include parameters such as equivalent widths, peak 2003. The single peak profile, which is sitting in a shallow ntensity relative to the continuum, full-width-at-half- broad emission feature, has a FWHM velocity of about maximum velocities, and for double peaked profiles, the 375±63 km/sec. The intensity of the emission line was elative intensities of the two peaks (Andrillat, 1983). This observed to be slightly stronger inJune. The H-beta profile Hows us to determine quantitatively any changes in line reported by Lacy (1977) for 12 July 1975 showed no >rofiles over time. emission with H-beta inabsorption. V1294 Aquilae was observed on 3 and 8July 2003. Fig. Results 8 shows that the profile remained unchanged. The single peak profile exhibits a symmetric broad base. The FWHM have observed over forty Be stars during 2003. Ten velocity is approximately 500+63 km/sec. f these stars are presented based on the criteria that they Observations of 59 Cygni from 23 June 2003 and 8July ad emission lines and were observed on multiple dates 2003 (Fig. 9) show nearly identical single peak profiles with iWeetween June 2003 and August 2003. The displayed spectra a FWHM velocity of about 600±63 km/sec. Journal of the Arkansas Academy of Science, Vol. 58, 2004

http://scholarworks.uark.edu/jaas/vol58/iss1/5 16 16 Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 5

Scott Austin

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Journal of the Arkansas Academy of Science, Vol. 58, 2004

http://scholarworks.uark.edu/jaas/vol58/iss1/5 18 18 Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 5

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Journal of the Arkansas Academy of Science, Vol. 58, 2004

Published by Arkansas Academy of Science, 2004 19 19 Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 5

Be Star Spectroscopy Using the UCA Fiber-Fed Spectrograph

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Journal of the Arkansas Academy of Science, Vol. 58, 2004 http://scholarworks.uark.edu/jaas/vol58/iss1/5 20

20 Journal of the Arkansas Academy of Science, Vol. 58 [2004], Art. 5 Scott Austin

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Be Star Spectroscopy Using the UCA Fiber-Fed Spectrograph

Fig. 10 shows the single peak profile of Omicron Dessart, L., and S. P. Owocki. 2003. Two-dimensional Aquarii. The data recorded on 24 July 2003 and 7 August simulations of the line-driven instability in hot-star 2003 show no significant change. The FWHM velocity of winds. Astron. Astrophys. 4O6:L1-L4. the profiles is about 430±63 km/sec. Fabregat, J., and Reig, P. 2000. Delta Scorpii. International Astron. Union Circ. 7461 Discussion and Conclusions Jaschek, M., A.Slettebak, and C.Jaschek. 1981. Be Stars Newsletter 4:19. The Be star that seemed to undergo the most Kannappan, S.J., and D.G.Fabricant 2000. Getting the variation of those we monitored on multiple dates was Chi most from a CCC spectrograph. Sky & Telescope Ophiuchi. The shape of the line profile (Fig. 3) did not July:125- 132. change, but the peak intensity and FWHM did change. Itis Kannappan, S. J., D. G. Fabricant, and C. B. Hughes. not clear from our data whether the variation is periodic or 2002. Building a CCD spectrograph for educational or random. We willattempt to monitor Chi Ophiuchi in 2004 amateur astronomy. Publ. Astron. Soc. Pacific 114: 577. with denser time coverage in order to resolve this question. Lacy, C. H. 1977. Rapid line variability. III.Search for Pi- 4 Aquilae, Beta^ Cygni, and Omicron Aquarii may have alpha and H-beta variability in Be, Of, and Wolf-Rayet changed slightly in intensity during our observations. We stars. Astrophys. J. 212:132-140. willneed to revisit these stars in the future as well in order Maintz,M.,T.Rivinus, S. Stefls, D.Baade, B. Wolf, and to verify how rapidly and by how much they may be R. H. D. Townsend. 2003. Stellar and circumstellar fluctuating. The long term goal of this project is to revisit activity of the Be star Omega Cma. Astron. Astrophys. our project stars as often a possible and necessary to record 411:181-191. the changes in the circumstellar disks. We then plan to Poe, C. H., and D.B. Friend. 1986. A rotating, magnetic, combine our data with those of other Be star researchers in radiation-driven wind model applied to Be stars. order to achieve an adequate record of the changes these Astrophys. J. 311:317. stars go through. This will then test the various Be star model scenarios by comparing the modeled line profiles and variations with the observed. Acknowledgments. —This research has been supported with grants from the following: Faculty Research Grant JCA University Research Council, Summer Stipend UCA University Research Council 2002 and 2003, NASA Arkansas Space Grant Consortium Research Infrastructure Grant. This research has also been assisted by the efforts of JCA Students Allan Holloway and Bart Dunlap.

Literature Cited

Y. 1983. Asecond catalog ofthe profile of the H- alpha line in 55 Be stars. Astron. Astrophys. Suppl. rdrillat,Series 53:319-338. K.M.2002. Support for a white dwarf in the Be rpparao,star binary gamma Cassiopeiae. Astron. Astrophys. 382:554-555. Aydin, C, and Faraggiana R. 1978. Spectroscopic study of the shell star 48 Lib (FX Lib). Astron. Astrophys. Suppl. Series 34:51-66 Banerjee, D. P. K., S. D.Rawat, P. Janardhan. 2000. H alpha observations of Be stars. Astron. Astrophys. Suppl. Series 147:229-242 Uranmer, S. R.,and S.P. Owocki. 1996. Hydrodynamical simulations of corotating interaction regions and discrete absorption components in rotating O-star winds. Astrophys. J. 462: 469-488.

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