**Abbreviations**

The following abbreviations are used in this manuscript:


### **Appendix A. Spectra of Stars in Vicinity of GR 290**

**Figure A1.** From the top panel downwards, spectra of the stars: J013459.8+304156.98, J013500.69+304207.5, J013500.9+304018.27 and J013501.87+304157.3. For comparison, the reddened spectra of HD 42543 (M1 Ia-ab), HD 154733 (K3 III), HD 146051 (M0.5 III) and HD 164353 (B5 Ib) are shown by red dashed lines.

**Figure A2.** From the top panel downwards, spectra of the stars: J013502.37+304332.1, J013503.29+304042.5, J013504.37+304253.1 and J013505.76+304102.21. For comparison, the reddened spectra of HD 128167 (F2 V), HD 102212 (M1 III) and HD 135722 (G8 III) are shown by red dashed lines.

**Figure A3.** From the top panel downwards, spectra of the stars: J013505.87+304114.2, J013506.14+304129.0, J013507.09+304212.4 and J013507.15+304156.3. For comparison, the reddened spectra of HD 126141 (F5 V), HD 101606 (F4 V) and HD 75532 (G8 V) are shown by red dashed lines.

**Figure A4.** From the top panel downwards, spectra of the stars: J013507.40+304132.5, J013509.63+304146.1, J013511.40+304250.8 and J013511.66+304408.3. For comparison, the reddened spectra of HD 146051 (M0.5 III), HD 50420 (A9 III) and HD 134169 (G1 V) are shown by red dashed lines.

**Figure A5.** From the top panel downwards, spectra of the stars: J013512.05+304327.2 and J013514.1+304423.21.
