Dr. Kutluay YÜCE

Dr. Kutluay YÜCE (associate professor)

Ankara University
Faculty of Science
Department of Astronomy and Space Sciences
Anadolu, Ankara
TR-06100 TURKEY
kyuce@ankara.edu.tr
+90 (312) 2126720 (1196)

Research Background:

I participated as an observer in the routine observation program on “the photoelectric photometry of the variable stars” carried out at the Ankara University Observatory. This work started in the fourth year of my BSc education and lasted about ten years covering my MSc and PhD studies. These observations have been the basis of my subsequent scientific work starting from 2003 up to now. The same observations have also been instrumental for gaining academic experience in photometric observations.

During the MSc education, I also carried out photometric observations of a high mass Be/X-ray binary X Persei system which was my thesis star. This work took about a three-years during which I also made some eclipsing binary star observations. The purpose of these observations was to determine the long time changes in the light emitted by the star. The changes are likely to result from the circumstellar disc around the Be component of the X Persei system. According to literature, X Persei was in its brightest state after the circumstellar disc-loss phase between 1990 and 1993.

The MSc thesis work entitled “The Spectral Analysis of Optical and Ultraviolet Spectra of X Persei” was a combination of photometric observations, optical spectral analysis and ultraviolet spectral findings. The photometric observations were done at the Ankara University Observatory; the optical spectra were provided by Prof. Dr. Semanur Engin based on her joint studies at the Trieste Observatory (Italy) and the UV data were supplied from the archieve of IUE (International Ultraviolet Explorer satellite).

The optical spectra included visible region of 3600-7000Å.The refinement of the Earth-based observational spectra (normalization to continuum, identification of emission and absorption lines, the line measurements by planimetry, etc) were done by usual techniques. It was also impressive for me to examine the effects of the circumstellar disc structure on the first lines of the Hydrogen Balmer series (H_alpha, H_beta). The circumstellar disc caused by the stellar wind gave rise to the emission structure in the line profiles. The emission lines were found to become to stronger and stronger in a time scale of months and then weaken within the same time scale; absorption lines becoming stronger.

The UV-spectral data within the wavelength region of 1200-3000Å were used for analysis. The normalization of the spectra to the continuum, determination of the line profiles, identification of individual lines, estimation of mass loss rate due to stellar winds from the observed Si IV and C IV ionic lines, the determination of stellar atmospheric parameters from a comparison of the observational energy distributions of low resolution with the theoretical ones by applying model atmospheres to the region spectra were all included in the UV analyses.

Both spectroscopic and the photometric analyses indicate the existence of an circumstellar disc around the optical counterpart of O9.5 spectral type. The disc partially or completely disperses in a time scale of years and then begins to form again. Publications based on this master thesis are given below :

• Engin, K. Yüce, “Photoelectric Observations of X Persei”,
Information Bulletin on Variable Stars, IBVS-No: 4454 (1997).

• Engin, K. Yüce, “Line Profile Changes in X Persei”, in
Information Bulletin on Variable Stars, IBVS-No: 4648, (1998).

During the time I have done my MSc studies Turkey had no spectrometers and no telescopes with an aperature greater than 0.30-m. The spectra analysed were taken at the Trieste Observatory (Italy) and the Dominion Astrophysical Observatory (Victoria, BC, Canada taken by Dr. Adelman) in collaboration with international co-workers.

I strongly wished to continue with spectral analysis of stars in my PhD studies. As such a study recquired observational data and in those days Turkish observatories did not have adequate facilities, it took me three years to get in touch with foreign Institutions and provide the spectra to surve as the basis of the analyses. Prof. Dr. Dursun Koçer helped me in that respect and introduced me to Prof. Dr. Saul J. Adelman. Prof. Dr. Adelman not only provided the spectra but also acted as a co-advisor in my PhD education. I used the computer codes he provided and the PhD work on the stellar chemical abundance analysis became possible.

During my PhD thesis the elemental abundance analysis of two early type supergiants 4 Lac and nu Cep were performed. In the thesis work entitled “The Spectral Analyses of 4 Lac and nu Cep Stars” under the supervision of Prof. Dr. Semanur Engin (Ankara University, emeritus) and Prof. Dr. Saul J. Adelman (The CITADEL, Charleston), high quality spectral data obtained with Reticon and CCD dedectors of the 1.2-m telescope at the Dominion Astrophysical Observatory (Victoria, BC, Canada) and provided by Dr. Adelman were used. A detailed process based on the measurements on the spectral lines of the stellar spectra of 4 Lac and nu Cep. The identification of the individual spectral lines were done; the atmospheric parameters (effective temperature, surface gravity, micro- and macro- turbulent velocities etc.) were estimated; the elemental abundances were calculated based on model atmspheres; and  the stellar evolutionary   scenarios available in the literature in the light of the evolutionary scenarios available in the literature, we have made a detailed examination of the evolution state of the stars.

A previous work I participated (S.J. Adelman, H. Caliskan, D. Kocer, H. Kablan, K. Yüce, S. Engin, “The superficially normal B and A stars alpha Draconis, tau Herculis, gamma Lyrae and HR 7926”, Astronomy and Astrophysics, 2001, vol. 371, 1078-1083) helped me a  lot in the PhD process. In that work I had already learnt how to determine the abundance of superficial elements by model atmosphere method through deciphering all the observed line profiles and other experience to conduct detailed spectroscopic studies with high resolution modern fine analysis techniques.

Publications based on my PhD thesis studies are as follows:

– Yüce, K. “Spectral Analysis of 4 Lacertae and nu Cephei”,
Baltic Astronomy, vol. 14, 51-82 (2005)

– Dissertation Summary in SCI: “Spectral Analyses of 4 Lacertae and nu Cephei”
Kutluay Yüce. The Publications of Astronomical Socities of the Pacific, vol. 115, issue 809, p.888 (2003).

– Poster in International Congress: “Abundances in 4 Lacertae and nu Cephei”,
Kutluay Yüce, In the A-Star Puzzle, held in Poprad-Slovakia, IAU- Symposium, No. 224, (Edited by J. Zverko, J. Ziznovsky, S.J. Adelman, and W.W. Weiss), Cambridge, UK: Cambridge University Press, pg.873-878 (2004).

– Lecture in National Congress: “Geç B/Erken A Tayf Türü Süperdev Yıldızlarından
4 Lacertae ve nu Cephei’nin Tayfsal  Analizleri”,
Kutluay Yüce, 31 Ağustos-4 Eylül 2004, Kayseri, XIV. Ulusal Astronomi Kongresi Bildiri kitabı, pg.81-85, in Turkish

During my astronomical adventure, the fact that the supergiant stars show photometric light variations in their short and long time-scale emission caught my attention. Later I performed the photometric observations of several stars in the Strömgren ubvyHb photometric system using an SSP5 photometer attached to the 0.40-m Cassegrain telescope at TÜBITAK National Observatory in Antalya, Turkey. Prof. Dr. Saul J. Adelman has done parallel observations on the same stellar objects using the ‘Four College Automated Photoelectric Telescope’, Arizona, USA.  We compared our observational data to see whether the like intensity changes in the photometric measurements depend on the ground location on Earth and found that the changes indicated were slightly bigger in Turkey (S.J. Adelman, K. Yüce, “Strömgren Photometry of the Supergiants HD 4841 (B5 Ia) and HD 194279 (B2 Ia)”, Baltic Astronomy, 2007, vol. 16, 311-326).

I teach in undergraduate and graduate programs of Ankara University Astronomy and Space Sciences Department. In 2005, I activated the graduate course “801512 – Chemical Abundance Analysis”. At present, my primary concern is to evoke a scientific consciousness and zeal in the young researchers of this country. I take them to the nearby observatories including the Turkish National Observatory (Antalya) and make them feel the taste of scientific observation as well as of inference and analysis.

Under my supervisorship the following graduate theses and the term projects were completed at Ankara University :

1) Thesis Title: “An Elemental Abundance Analysis of Low Amplitude delta Scuti Star: 20 CVn”

Student: Tolgahan Kılıçoğlu (reserach asistant) (MSc, completed: January 2008)

In this work, the atmosphere paramaters and elemental abundances of delta Scuti type 20 CVn (F3 III) were determined using high quality spectral data obtained with Reticon and CCD dedectors at the long camera of the coude spectrograph of the 1.2 m telescope at the Dominion Astrophysical Observatory. Our results of the abundance analysis show that it is a marginal metallic-lined star.

2) Term Project Title: “Spectral measurements of HD 43866 (B9 II) using
TÜBİTAK National Observatory-Coude Echelle Spectra”

Student: Rahime Canan Şahin (MSc Term Project-completed: June 2008)

In this study detailed spectral analysis performed of HD43866 (B9 II) was done using  the observed spectra obtained with coude echelle spectrograph of 1.5-m RTT150 telescope at Turkish National Observatory (TUG, Antalya). The analysis we performed using TUG spectra in the region of 3900-877Å was in a manner similar to that of Kutluay Yüce’s PhD thesis, Tolgahan Kılıçoğlu’nun master thesis and the papers of Prof. Dr. Saul J. Adelman and associates series “Elemental abundances from DAO spectrograms”. The study is among the first detailed spectral analyses of TUG observation facilities.

3) Thesis Title: “Chemical Abundance Analysis of HD 39866 (A2 II) using TÜBİTAK National Observatory-Coude Echelle Spectra”

Student: Fatma Başak Eminoğlu (MSc-completed: July 2009)

The chemical abundance analysis of the HD39866 (A2 II) using the observed spectra taken with RTT150 telescope at TÜBITAK National Observatory (TUG, Antalya) which supplied by İlfan Bikmaev (Kazan, Russia) to Prof. Dr. Saul J. Adelman were firstly performed  under my supervision. Through these works, that TUG data could be used In the detailed spectral analysis of stars was determined. The reliable photospheric abundances which derived from performed the abundance analyses using high resolution TUG spectral data and state of the art measurement techniques indicates applicability of the technique used which are similar to those of Dr. Kim Venn (1995a,b) to TUG data.

4) Thesis Title: “Spectral Reductions and Chemical Abundance Analyses of the Stars

89 Cet and 29 And using TÜBITAK National Observatory (TUG) Coude Echelle Spectra”

Student: Sıla Eryılmaz (MSc-completed: November 2011)

In this thesis study the reduction of the spectrograms of 29 And and 89 Cet and then chemical abundance analyses were performed. The stars were observed with Coude Echelle Spectrograph of RTT150 Telescope at the TÜBİTAK National Observatory (TUG, Antalya) by Dr. Kutluay Yüce wihin the project as called “Chemically Abundance Analyses using CES Spectra of A, early-F, Am and Fm Stars” on August 2009. The detailed spectroscopic studies of TUG data were determined and recorded by comparing the results of the study with those of the literature in order to determine the suitability of TUG data for detailed spectral analyzes.

5) Term Project Title: “Stellar Spectrophotometry”

Student: Lütfiye Erkuş (MSc Term Project-completed: June 2012)

In the study we investigated stellar optical region spectrophotometric analyses. The study includes spectrophotometric observational techniques under the leadership of Prof. Dr. Saul J. ADELMAN (The Citadel), an overview of soon to be working ASTRA Cassegrain Spectrophotometer and its automated 0.5-m f/16 telescope, the reduction of the observational data, and flux calibrations. The new ASTRA spectrophotometer uses a CCD as a detector and will produce higher quality data the rotating grating scanners with which most of the optical region stellar fluxes have been obtained. Optical spectrophotometry will soon become an excellent tool to study stellar variability. Relative to filter photometry one will have many more points to study of the stellar energy distribution. The effect of convection, turbulence, magnetic fields, rotation, and broad-continuum features on the observed stellar flux distribution are discussed. After the most-commonly used methods for determining the stellar atmosphere parameters -photometry, spectrophotometric fluxes and Balmer line profiles, and the infrared flux method- are presented, the advantage and disadvantage of spectrophotometry are examined.

6)  Thesis Title: “Physical and Chemical Properties of Normal A Star Atmospheres”

Student: Senem Erden ÇABUK (MSc – completed: August 2016)

Here we study the atmospheric characteristics of the both kinds ‘normal’ and ‘metallic-lined chemically-peculiar’ of A type stars. Using high resolution stellar spectral analyses the physical properties and chemical structures of A type stars were found from the common features and the unique characteristics of stars. The spectral data used for this purpose are the Main Sequence Band chemically ‘normal’ late B – early F stars from the study by Yüce and Adelman (2014) who used high dispersion spectrograms taken with CCD detectors at the Coude spectrograph of the1.22-m telescope of the Dominion Astrophysical Observatory.]

Current Research:

Recently, I have focused on the possibility of supplying more refined spectra from the 1.50-m telescope’s coude echelle spectrograph of TÜBİTAK National Observatory in order to minimize the dependence on the spectral data of the overseas observatories. Due to the absence of any scientific work demonstrating observational spectral quality and its use in chemical analysis, my primary goal and target is to achieve a signal-to-noise ratio (S / G)> 200, a requirement expected to be met in the literature. With the technique of coaddition, we have reached S/N values greater than 500 (Yüce ve ark. 2008, XVI. Ulusal Astronomi Kongresi Bildiri Kitabı, Ç.O.M.Ü. yayınları, no:37, s.1076-1089; in Turkish).

I would to emphasize say that I will have to be continuing to work on the reduction of the spectral observations, measurements and analyses using TUG observation facilities. I think it is important to examine the spectra provided from our National Observatory and from other spectrographs that will be operative in our country in detail with high sensitivity.

I worked on “stellar model atmospheres and synthetic spectral analyses” under the consultation of Fiorella Castelli in a scientific visit under the “TUBITAK Post-Doctoral Research Scholarship” to the Trieste Observatory (INAF-Osservatorio Astronomico) for 12 months on February 2010. Stellar model atmospheres form the basis for any element abundance determination, which are crucial ingredients for studies of stellar, galactic and cosmic evolution. Thanks to the efficient spectrographs available nowadays, the uncertainties tend to become more and more negligible. This implies the need of further improvements in the stellar atmosphere modeling and atomic data determinations. As a result of our studies in Italy, we have developed a spectral atlas and astrophysical data of Xe II atomic data that are yet to be observed in laboratory conditions (Yüce, K.; Castelli, F.; Hubrig, S. “Wavelengths and Oscillator Strengths of Xe II from the UVES Spectra of Four HgMn Stars”, Astronomy and Astrophysics, vol. 528, A37 1-16, 2011).

The basic knowledge of astrophysics is derived from detailed spectroscopic studies of stars. This most important and most efficient knowledge area of astrophysics is the basic research area of a few research centers in the world. For many years, Trieste (Italy) has stood as a forerunner as to the beginning of them.

I applied for the associate professorship exam given by the Interuniversity Board of Turkey in April 2011, and got the title in the first exam on October 2012.

In recent years, I have tended to the astrophysical problems of the stars in the neighborhood of the late B – middle F spectral range.

I nowadays concentrate on the determination the stellar parameters with photometric, spectrophotometric and spectroscopic methods. As a facility to provide the best data for this prupose is the ASTRA Cassegrain Spectrophotometer and its automated 0.5-m, f=16 telescope in Arizona which is expected to be at work soon. With the ASTRA spectrophotometer set up by Prof. Dr. Adelman of The CITADEL we hope to better determine both effective temperatures and surface gravities which are needed to produce stellar model atmospheres and hence will result in a reduction of the uncertainties of the derived chemical abundances.

Visiting ‘The CITADEL, Charleston’ will be a good opportunity for me to learn about the most recently constructed tools for comprehensive stellar analyses and to polish my skills. This will give me more time at ASTRA Cassegrain Spectrophotometer, because the details of the observations there will have to have been planned together with Prof. Dr. Adelman. When I return to Turkey I am hoping to transfer what I learnt to the graduate students who are likely to work on stellar spectroscopy.