Spectroscopy Section - Recommended Projects

Pulsating stars

Observations of pulsating stars allow researchers to note trends between spectroscopic and photometric observations which reveal processes in various layers of stellar atmospheres. These trends then lead to a physical understanding of the star, and formation of relevant models of atmospheric dynamics.

RV Tauri variables

by Ryan Maderak

Spectra will enable studying radial velocity curves and line profiles in order to examine the complex motions within the atmosphere

At maximum light, high resolution (R > 10,000) is required, and high SNR of 80 – 100 per pixel. At minimum light: SNR could be as low as 50. This will require total integration times of 30 - 60 minutes on small scopes.

Wavelength coverage: H-alpha +/– 100 angstroms, erring on the red ward side if spectral range is limited.

Desired cadence: as frequently as possible, at least one spectrum per night.

RV Tauri variables
Name Period (days) Bright mag. Faint mag.
R Sct 140 4.9 6.9
U Mon 92 5.1 7.1
AC Her 75 6.4 8.7

Mira variables

by Ulisse Munari

Medium-to-low resolution spectrographs (dispersion higher than 2 AA/pixel)

  • There are no special requirements to be able to measure the depth of molecular bands (e.g. TiO). A dispersion between 2 and 6 °A/pix will do fine.
  • Are there shocks in the pulsating atmosphere (derived from the relative strength of Balmer lines – strength of H-alpha, vs strength of H-beta vs strength of H-gamma)?

High resolution spectrographs (need dispersion 0.2 °A/pix or better)

  • Radial velocities (RVs) of Balmer lines, covering the pulsation cycle - Are there long-term variations in the light curves of such objects with time?
  • Is there a variation of the shape of the RV curve with the pulsation period?
  • Compare RV changes of various types of Mira variables - similarities and differences
  • How does the RV curve obtained from measurements at the center of strong molecular bands compare with RV measurements of lines away from molecular bands ? Do we see different amplitudes? Different phases perhaps ?

For both high and low resolution spectra

  • How does the profile of an emission line change in shape (multiple peaks, asymmetric shapes, super-imposed sharp absorption components, etc.) along the pulsating cycle? (focus on H-alpha line)

Desired cadence: 1 spectrum per star per week.

Mira variables
Name Period (days) Bright mag. Faint mag. Spectral type
R And 409.2 5.8 15.2 S3,5e-S8,8e(M7e)
omi Cet 331.96 2.0 10.1 M5e-M9e
Y Per 248.60 8.1 11.3 C4,3e(R4e)
R Lep 427.07 5.5 11.7 C7,6e(N6e)
S Cam 329.9 7.7 11.6 C7,3e(R8e)
R Gem 369.91 6.0 14.0 S2,9e-S8,9e(Tc)
V Cnc 269.7 7.6 13.3 S0e-S7,9e
R Leo 309.95 4.4 11.3 M6e-M8IIIe-M9.5e
S UMa 225.87 7.1 12.7 S0,9e-S5,9e
R Hya 388.87 3.5 10.9 M6e-M9eS(Tc)
V CrB 357.63 6.9 12.6 C6,2e(N2e)
V Oph 297.21 7.3 11.6 C5,2-C7,4e(N3e)
X Oph 328.85 5.9 9.2 M5e-M9e
R Aql 269.84 5.3 11.9 M5e-M9IIIe
khi Cyg 408.05 3.3 14.2 S6,2e-S10,4e(MSe)
U Cyg 463.24 5.9 12.1 C7,2e-C9,2(Npe)
T Cep 388.14 5.2 11.3 M5.5e-M8.8e
X Aqr 311.4 7.2 15.0 S6,3e:(M4e-M6.5e)

Cepheids and RR Lyrae variables

by Róbert Szabó and the TESS RR Lyrae and Cepheid survey team

For Cepheids and RRLs, spectroscopy is particularly useful to determine radial velocity curves of the star, and explore changes of the line profiles along the pulsation cycle. Radial velocity studies are based on as many metallic lines as possible, so echelle spectra (R~10,000) with a broad wavelength range are the best. Also, line profile variations (variations in the shape of the spectral line) can give more detailed information about motions in line-forming regions (and about the geometry of the pulsations, as for those stars the main pulsation is radial). Lower resolution spectra covering the optical range around 4500 - 6500 AA are needed to detect line profile changes during a pulsation cycle.


Either a broad coverage in the optical 4500-6500\AA for precision RVs, or individual lines (such as Halpha, Ca II triplet) that could be expected to show some interesting variability or shock phenomena.

RR Lyrae variables

Broad coverage in the blue/optical 4000-6500\AA, Balmer lines and the D3 Helium line at 5872 AA are of interest. Slightly bluer wavelengths might be better for RR Lyraes, because there are pulsation phases when their spectrum becomes rather featureless.

Integration times should be adjusted based on the pulsation period of the star. A spectrum per 0.05 phase units (or better) is a good coverage for all pulsation periods, especially if the pulsation period is less than a day.

Cepheids with X-ray flashes

Requesting any resolution spectra, preferably 1/day or more frequently. Interesting lines: Balmer (absorption) at different phases of the pulsation period.

Name Bright mag. Faint mag. Notes
XZ Cet 9.24 9.71 prototype of Anomalous Cepheids
BL Her 9.70 10.62  
V553 Cen 8.21 8.74 C-rich Cepheid
RT TrA 9.43 10.18  
RR Lyrs
Name Bright mag. Faint mag. Notes
RR Lyr 7.17 8.14 prototype; changing Blazhko; additional pulsation modes
MT Tel 8.70 9.25  
RZ Cep 9.15 9.72  
SV Hya 9.78 11.0  
SU Dra 9.18 10.27  
X Ari 9.04 9.97  
Cepheids with X-ray flashes
Name Bright mag. Faint mag. Notes
Polaris 1.97 2.00 period is increasing
Delta Cep 3.49 4.36  
V473 Lyr 5.99 6.35  
V1334 Cyg 5.77 5.96  
VY Pyx 7.13 7.40  

Emission stars

Observations of emission lines allow researchers to study winds and probe circumstellar environments. Low resolution spectra can be used to track changing equivalent widths, while high resolution observations open the possibility of decoding the velocity and spatial distribution of material in the system. In many cases, timeseries observations of emission stars will reveal changes across a wide range of timescales.

Chromospherically active stars

Emission regions: Hydrogen and Ca II H & K lines (chromospheric emission); Absorption features: Ca II H & K lines. Looking for EW changes. Resolution at least 1000. Observe once/week.

Chromospherically active stars
Name Average Mag.
chi Dra 3.5
UV Cet 6.8-13.0
eps Eri 3.73
Barnard's star (V2500 Oph) 9.55
RS CVn 8-9
BF Lyn 7.7

Wolf-Rayet (WR) outflows

by Noel Douglas Richardson

Emission: highly ionized He, Si, O, N or C; strong stellar winds with P Cygni absorption profiles; enhanced heavy elements. Lines change with time, as winds evolve and expand. Study long-term evolution of line profiles, and evolution of P-Cygni. Great targets for star analyzers!

Desired cadence: 1 spectrum per night or continuous monitoring.

Name Bright mag. (V) Faint mag. (V) Spectral type
Eta Car -1.0 6 pec(e)
tet Mus 5.5 5.52 E/WR (WC6+O9.5I)
DO Eri 5.97 6 A5p(Sr-Cr-Eu)
V1770 Cyg 7.36 7.52 WR
V1687 Cyg ~4   WR
V1679 Cyg 7.86 7.93 WR

Semi-detached systems

by Christian Knigge and Stella Kafka

Semi-detached binaries consist of a white dwarf accreting material from a low-mass main sequence or giant donor star. Most of the light observed in those systems is accretion generated (accretion disk, hotspot on the disk, accretion column), and is quite variable in all wavelengths. Depending on the optical state, the spectrum can change from broad emission to broad absorption; depending on the phase of the orbital cycle and the inclination of the system, the line strength may also change. Therefore, both phase-resolved spectra and long-term monitoring provide valuable information on the accretion process and variability of the system.

Snapshot spectra of CVs are abundant in the literature. However there has not been a systematic monitoring of any one system on timescales of years. The AAVSO observers have been meticulous in acquiring photometry on a number of key targets in the north and southern hemisphere, so their photometric behavior is reasonably well characterized. In parallel with photometry, we request similar long-term monitoring of a selected targets. Desired cadence is one spectrum/day or (in the case of phase-resolved targets) one spectrum/0.1 phase units. All resolutions.

Dwarf novae

Spectra requested in quiescence or outburst (and everything in between). Spectra can track changes as the system gets bright/faint, assess differences between quiescence states, compare the rise to/from outburst etc.

Nova-like CVs

Dwarf novae in quiescence or outburst (and everything in between). Spectra can track changes as the system gets bright/faint, assess differences between quiescence states, compare the rise to/from outburst etc.

Dwarf novae
Name Period (days) Bright mag. Faint mag. Notes
SS Cyg 0.275 7.7 12.4  
U Gem 0.176 8.2  14.9  
VW Hyi 0.074 8.4 14.4  
GK Per 1.997 9.5 14.0 Nova Per 1901
Nova-like CVs
Name Period (days) Bright mag. Faint mag. Notes
IX Vel 0.194 9.1 10  
RW Sex 0.245 10.39 10.84  
V3885 Sgr 0.207 10.27 10.51  
TT Ari 0.137 10.2 16.5 High/low states
V603 Aql 0.138 11 12.4 High/low states
MV Lyr 0.133 12.2 18 Deep low states
Miscellaneous peculiar CVs
Name Period (days) Bright mag. Faint mag. Notes
BT Mon 0.334 14.5 16.4 deep eclipses
QU Car 0.454 10.9 11.7 outflows?
V Sge 0.514 8.6 13.9 prototype - bright/faint states
AE Aqr 0.412 10.18 12.12 Propeller


Microquasars are X-ray binaries which exhibit ultra-relativistic bipolar outflows. In these systems, a stellar mass compact object (either a neutron star or black hole) accretes matter from a supergiant companion star through an accretion disk. Emission lines come from the accretion process (disk, disk hotspot or stream) or the mass-donor star. Spectral lines lines such as H-alpha) and He I line at 6678˚A are usually visible and variable depending on the state of the system. Especially the He I 6678˚A line is valuable for the measurement of reliable radial velocities of the primary component to get a constraint on the orbital parameters of the system.

Spectral resolution of ~1000 or higher are required to measure EW, RV and FWHM variations of those lines, and S/N of more than 20. Exposure times need to be adjusted accordingly.

Name Period (days) Mag. range (V)
V1357 Cyg (Cyg x-1) 5.6 8.72-8.93
V1313 Aql (SS433) 13.1 12.5 - 15.2
V0615 Cas 26.5 10.4-11.1
V4641 Sgr 2.8 9.0-13.8
V0479 Sct 3.9 ~11.3
HD215227 60.4 ~8.7
NSV 16907 320 ~9.1

Individual targets of interest

Many of these targets come from active alerts and campaigns; their desired cadence is "as frequently as possible."

Please follow the alert link for more information on spectroscopic requirements of observations.

Individual targets of interest
Name Var type Mag. range Alert link Notes
R Aqr pulsating 5.2-12.4 V Alert 696 spectroscopy needed during eclipse
b Persei eclipsing 4.55-4.75 Alert 655 spectroscopy needed during eclipse
N Nor 2018 nova 10.5 (at discovery) Alert 653 all resolutions, all spectral ranges
V1307 Ori HerbigAeBe  9.48-9.83 V Alert 657 H-alpha spectroscopy, all resolutions
R Mon HerbigAeBe 11-13.8 B Alert 657 H-alpha spectroscopy, all resolutions
V1410 Ori HerbigAeBe 9.39-9.73 V Alert 657 H-alpha spectroscopy, all resolutions
V346 Ori HerbigAeBe 10.1-10.9 V Alert 657 H-alpha spectroscopy, all resolutions
V1295 Aql HerbigAeBe 7.87-7.89 V Alert 657 H-alpha spectroscopy, all resolutions
S5 1803+78 BLLAC 13.8-18.1 V   unusual behavior
V725 Sgr LB 11.9-14.4 V   changing period?

Spectroscopic binaries
Name Period (days) Mag. outside eclipse Notes
b Persei 1.53 4.6 hierarchical triple
Beta Per (Algol) 2.87 2.1  
zeta Cen 2.29 2.5  
bet Lyr 12.94 3.3  
AP Psc 96.44 6.04  
TV Cas 1.81 7.22